Developed by:University of Kentucky Multidisciplinary Extension Team

Written by:Morris Bitzer, Agronomy, Co-EditorJames Herbek, Agronomy, Co-Editor

Ric Bessin, EntomologyJ.D. Green, Agronomy

Greg Ibendahl, Agricultural EconomicsJames Martin, Agronomy

Sam McNeill, Biosystems and Agricultural EngineeringMichael Montross, Biosystems and Agricultural Engineering

Lloyd Murdock, AgronomyPaul Vincelli, Plant Pathology

Ken Wells, Agronomy

Partial financial support for some of the research reported in this manualas well as full financial support for the printing provided by

the Kentucky Corn Growers Association.

A Comprehensive Guide to

CORN MANAGEMENTI N K E N T U C K Y

Mention or display of a trademark,proprietary product, or firm in text or figuresdoes not constitute an endorsement and doesnot imply approval to the exclusion of other

suitable products or firms.

Contents

Introduction ................................................................................................... 5Types of Corn ......................................................................................... 5Special-Purpose Corn ......................................................................... 6White and Yellow Food Grade Corn .............................................. 6

Corn Growth and Development ............................................................ 7

Tillage Systems ............................................................................................. 8Soil Compaction ................................................................................... 9Summary ............................................................................................... 10

Hybrid Selection ......................................................................................... 11Yield ......................................................................................................... 11Maturity .................................................................................................. 11Growing Degree Days (GDD) ......................................................... 12Corn Seed .............................................................................................. 12

Impact of Biotechnology ........................................................................ 13

Planting Practices ...................................................................................... 14Planting Date ....................................................................................... 14Planting Depth .................................................................................... 14

Cropping Rotation Benefits .................................................................. 16

Fertility Management .............................................................................. 17Introduction ......................................................................................... 17Soil Sampling ....................................................................................... 17Fertilizer Recommendations ......................................................... 18Crop Sufficiency .................................................................................. 18Nutrient Balance ................................................................................. 18Maintenance Fertilization ............................................................... 18Combination of Philosophies ........................................................ 18Summary of Fertilizer Recommendation Philosophies ...... 19Liming ..................................................................................................... 19Nitrogen ................................................................................................. 21Nitrogen Fertilizers ............................................................................ 22Upland Soils Wet from Constant Rains ...................................... 23Lower Soils with Short Periods of Flooding

(One to Two Days) .................................................................... 23Nitrogen Soil Test ............................................................................... 23Phosphorus and Potassium ........................................................... 24Secondary Nutrients and Micronutrients ................................ 24Other Nutrients ................................................................................... 25Row Fertilizers ..................................................................................... 25Expected Yield Response to Row Fertilizer ............................. 25Plant Analysis ....................................................................................... 25Sampling ................................................................................................ 26Sufficiency Level of Nutrients ....................................................... 26Nutrient Content and Removal by Corn ................................... 26

Weed Management ................................................................................... 27Life Cycles of Weeds .......................................................................... 27Weed Scouting .................................................................................... 27Weed and Corn Interactions .......................................................... 28Impact of Tillage ................................................................................. 28Cultural Practices and Mechanical Controls ........................... 29Herbicide Use and Timing .............................................................. 29Herbicide Persistence and Carryover ......................................... 30Herbicide Interactions ..................................................................... 31Herbicide-Resistant Weeds ............................................................ 31Herbicide-Tolerant Corn Hybrids ................................................. 32Other Information .............................................................................. 32

Disease Management .............................................................................. 33Preplant Decisions That Affect Disease Development ....... 33Crop Rotation ....................................................................................... 33Resistant Hybrids ............................................................................... 33Tillage ...................................................................................................... 34Other Cultural Practices .................................................................. 34Fungicides ............................................................................................. 34Scouting for Diseases ....................................................................... 34Mycotoxins ............................................................................................ 34Diseases of Corn ................................................................................. 35Acknowledgment .............................................................................. 41

Insect Pests ................................................................................................... 42Insect Resistance through Biotechnology ............................... 42Pest Monitoring Procedures .......................................................... 42Key Factors ............................................................................................ 42Major Pests ............................................................................................ 42

Economics for Corn Production .......................................................... 48Enterprise Budgets ............................................................................ 48Partial Budgets .................................................................................... 49Cost Concepts ...................................................................................... 49Economic Concepts .......................................................................... 50Opportunity Cost ............................................................................... 51

Corn Harvesting, Handling, Drying, and Storage ....................... 52Introduction ......................................................................................... 52Preparing for Harvest ....................................................................... 52Harvest Considerations ................................................................... 52Where Do Combine Losses Occur? ............................................. 53How to Measure Combine Losses ............................................... 53Adjustments to Improve Combine Performance .................. 54Economic Incentive to Reduce Harvest Losses ...................... 54Drying Considerations ..................................................................... 54Storage Considerations ................................................................... 55

Marketing ...................................................................................................... 59Pricing Methods ................................................................................. 61Contract Delivery Periods ............................................................... 62Timing of Grain Sales ........................................................................ 62Factors Influencing Pricing Decisions ....................................... 62Conclusions .......................................................................................... 63

References ..................................................................................................... 64

5

IntroductionMorris Bitzer and James Herbek

The corn (Zea mays L.) grown in Ken-tucky is used mainly for livestock feed(60 percent) and as a cash crop. As acash crop sold from the farm, cornranks third behind tobacco and soy-beans but is the number one row cropin terms of acreage. However, in totalcrop value, as reported by the KentuckyAgricultural Statistics Service, cornranks third after tobacco and hay. Cornis grown in every county in Kentucky,with a major portion of the acreage inWestern Kentucky. Corn acreage inKentucky dropped from a high of 3.6million acres in 1911 to a low of 1.13million acres in 1972. Acreage in-creased slightly in the 1980s to an av-erage of 1.5 million acres but thendeclined to an average of 1.34 millionacres in the 1990s (Figure 1).

Corn yields have risen dramaticallyover the last few decades. The aver-age state yield in the 1970s was 85.5bushels per acre; in the 1980s, 94.1bushels per acre; and in the 1990s,112.0 bushels per acre. Since 1990,

the highest state average ever was 132bushels per acre in 1992, and the low-est average during this period was 100bushels per acre in 1991.

Because the cost of producing anacre of corn is high and the value perbushel has declined in recent years,producers must manage and markettheir corn crop more carefully for ad-equate profits. The goal of this publi-cation is to serve as a guide for cornproduction strategies that focus on ef-ficient use of resources and provide theprinciples and practices for obtainingmaximum, profitable corn yields.

With the introduction of biotech-nology in the marketplace, producersnow have to make a new decisionwhen selecting corn hybrids. Biotech-derived crops have been altered andimproved to include resistance or tol-erance to pesticides and improved foodand feed qualities. A more thoroughdiscussion of the impact of biotechnol-ogy on corn production is presentedlater in this publication.

Types of CornCorn may be classified by kernel

characteristics such as dent, flint,flour, sweet, pop, and pod corn. Ex-cept for pod corn, these types arebased on the endosperm composi-tion of the kernel. The quantity orvolume of endosperm determinesthe size of the kernel (e.g., the dif-ference between dent and flint cornsor flint corn and popcorn) is poly-genic (controlled by many genes).The pod corn trait is monogenic andmore of an ornamental type.

This publication deals mostly withthe dent corns that originated from thehybridization of the southern dent orlate-flowering maize race calledGourdseed and the early-floweringnorthern flints. Dent corn is charac-terized by the presence of corneous,horny endosperm at the sides and backof the kernels. The central core is a soft,floury endosperm extending to thecrown of the endosperm where, upondrying, it collapses to produce a dis-tinct indentation.

Dent corn is used primarily as ani-mal food but also serves as a raw mate-rial for industry and as a staple food.There are two types of dent corn, yel-low and white. Except for some sweetcorn and popcorn, dent corn is themain commercial type of corn grownin Kentucky. The majority of dent cornin Kentucky has yellow kernels; how-ever, Kentucky is one of the leadingstates in the production of white corn,which is grown mainly for the foodindustry and is about 10 percent of thetotal corn acreage. In 1995, Kentucky

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had 116,000 acres of white corn, andthis acreage remains fairly constantfrom year to year. Very little flint orflour corn is grown in the UnitedStates. Pod corn is mainly a curiosityand is not grown commercially.

Special-Purpose CornSome corn hybrids have been al-

tered genetically to produce changesin starch, protein, oil, or other proper-ties of the kernels. Some of these spe-cial-purpose corns grown in Kentuckyare waxy, high-amylose, high-lysine,high-oil, and low-phytate varieties. Avery limited acreage of waxy and high-amylose corn is being grown, and onlya few swine producers are raising high-lysine corn, but several thousand acresof high-oil corn are contracted eachyear in Kentucky.

Waxy corn is used as the raw ma-terial for the production of waxy corn-starch by wet-corn millers for industryand food uses. Waxy cornstarch con-tains more than 99 percent amylopec-tin, whereas regular corn contains 72to 76 percent amylopectin and 24 to28 percent amylose. High-amylosecorn has an amylose content greaterthan 50 percent. It is grown exclu-sively for wet milling for the textileindustry, gum candies, biodegradablepackaging materials, and as an adhe-sive in the manufacture of corrugatedcardboard. High-lysine corn containsthe single recessive gene, opaque-2,that reduces the zein in the en-dosperm and increases the concentra-tion of lysine, thus improving thenutritional quality of the grain. Its pri-mary use in the United States is feedfor nonruminants.

The most recent improvement inspecial-purpose corn has been the de-velopment of hybrids with higher con-centrations of oil. The high-oil seedsare produced by a topcross procedurein which the planted seed is a mixtureof 9 percent of a very high-oil inbredpollinator seed and 91 percent seed ofa male-sterile, high-yielding, single-cross hybrid. The seed produced con-tains upwards of 8 percent oilcompared to a normal hybrid, whichcontains only 3.5 to 4 percent oil. Theadded oil makes a high energy feed.Most high-oil corn is contracted andsold at a premium price. The averageyield of these high-oil hybrids has usu-ally been about 10 percent lower thannormal hybrids. It is usually recom-mended to plant these at a 10 percenthigher seeding rate in an effort to off-set some of this yield loss.

Another recent development hasbeen the testing and release of low-phytate corn hybrids. Phosphorus inregular corn is stored as phytate, butphosphorus in kernels of low-phytatecorn is digested more efficiently. Thisresults in lowering the need for supple-mental phosphorus, better use of thephosphorus by the animal, and lessphosphorus excreted into the envi-ronment. Initial tests of low-phytatecorn hybrids have been encouraging,but economic viability remains to bedetermined.

Special-purpose corns are usuallygrown under contract at a price pre-mium. It is important to understandthe contract requirements before thespecial-purpose corn is grown. Theremay also be certain recommended pro-duction management practices, e.g.,soil type, fertility, population, planting

date and harvest, drying, and handlingpractices to obtain the highest possibleyields while maintaining grain quality.It is important that grain identity ofspecial-purpose corns be preservedfrom planting through storage to avoidcontamination that would eliminatepremium prices and decrease market-ability. Special-purpose corns also re-quire isolation from other corn toeliminate cross-pollination.

Most, but not all, special-purposecorns have an inherently lower yieldcompared to normal dent-corn hy-brids. However, special-purpose cornscan compensate for this reduction inyield potential with adequate premi-ums. Before producers decide to growa specialty corn, it is imperative thatthey determine potential yield reduc-tions, production risks, contract re-quirements, and the premium amountneeded to ensure a profitable return.Because of improved hybrid develop-ment, the yield of some specialty cornshas improved as compared to normalhybrids.

White and Yellow FoodGrade Corn

Kentucky is one of the leading statesin the production of white and yellowcorn for food. Food grade corn is usedto make corn flakes, tortilla flour, andcornmeal. The hybrids for this marketare usually selected by the company of-fering the production contract. Theregional testing of the yellow food cornhybrids has been discontinued; how-ever, the white food corn hybrids arestill being tested, and results are avail-able from the University of Kentuckycorn testing program.

7

Corn Growth and DevelopmentMorris Bitzer and James Herbek

no effect on the growing point or fi-nal yield.

After the tassel and all the leavesand ear shoots are initiated, the stalkbegins a period of rapid growth. Whensix or seven leaves have fully emerged,the growing point has moved abovethe soil surface and any damage to theleaves and growing point could affectfinal yield. Plant height increases dra-matically during this rapid growthphase, and the plant reaches its maxi-mum height when the tassel is fullyemerged from the whorl. Although theear shoots were formed just before tas-sel formation (five leaves emerged), thelength of the ear and potential num-ber of ovules or kernels per row is de-termined between the development of10 or 11 emerged leaves to 17 or 18emerged leaves or about one week be-fore silking. Moisture or nutrientstresses during this period of ear sizedetermination may seriously reduce thenumber of potential seeds on an ear.Earlier maturing hybrids will advancethrough these stages in a shorter time,which usually results in smaller earsthan later maturing hybrids. The nodalroot system is developing rapidly dur-ing this stage, which allows for morerapid uptake of soil nutrients and wa-ter to meet the demands of this rapidgrowth rate. At tasseling, less than halfof the final weight of the corn planthas been produced; however, morethan 60 percent of the nitrogen, 50percent of the phosphorus, and 80 per-cent of the potassium uptake have al-ready occurred.

As vegetative growth nears comple-tion, the ear develops very rapidly. Theflowering stage, which includes polli-nation, is the most critical period inthe development of the corn plant.The flowering stage occurs about 65days after corn emergence in a mediummaturity hybrid. Pollen shedding be-gins two to three days after the tasselhas fully emerged from the last leaf

A cornfield is a complex and con-stantly changing community made upof many individual corn plants. Withinthe corn plant, the raw materials (wa-ter and minerals from the soil and car-bon dioxide and oxygen from theair)—with sunlight providing the en-ergy—combine to produce yield. Thegrowth and yield of a corn plant arefunctions of the plant’s genetic poten-tial to interact with its environmentalconditions. Although climatic condi-tions account for a major portion of theenvironmental influence on corngrowth and development, a corn pro-ducer can manipulate the environmentwith various management practices. Byunderstanding how a corn plant devel-ops, a producer can use the proper pro-duction practices to obtain higheryields and profit. Following is a briefdiscussion of the growth and develop-ment of the corn plant.

The corn seed contains adequatestored nutrient reserves to get theseedling established. Seedling emer-gence usually occurs six to 10 days af-ter planting (four to five days underwarm, moist soil conditions). If theseed is placed in a cool, dry soil, it maytake two weeks or longer for seedlingemergence. The depth of planting alsowill influence how long it takes for theseedling to emerge. The depth atwhich the permanent root system(nodal roots) develops is not affectedby planting depth and occurs approxi-mately 1 inch below the soil surface.Three or four fully developed leavesare produced during the first threeweeks after the plant emerges. A leafis fully developed when the collar ofthat leaf is visible. Initiation of all theleaves, ear shoots, and tassel has oc-curred at the growing point by thisstage, and the growing point of theplant is still approximately 1 inch be-low the soil surface. Damage to theseedling above the ground from frost,hail, or livestock would have little or

sheath and just prior to silk emergence.Under favorable conditions, all silkswill emerge within three to five daysafter tasseling, and the tassel will con-tinue to shed pollen for five to eightdays. The silks from near the base ofthe ear emerge first, and emergenceprogresses up the ear to the tip. Whena pollen grain falls on a corn silk, itgerminates and produces a pollen tubethat grows the length of the silk inabout 24 hours, after which fertiliza-tion occurs and a new kernel begins todevelop. The silk is released by thekernel immediately upon pollination.Stress (moisture, temperature, nutri-ent) from one week before to one weekafter flowering may delay silking untilafter most of the pollen is shed, result-ing in poor pollination, especially onthe tips of the ears.

Grain production occurs betweenpollination and maturity. Drought ornutrient stress during this period canresult in unfilled kernels, less weightper kernel, and light, chaffy ears. Thegrain filling period covers about 55 daysfor most corn hybrids. Plant physiologi-cal maturity is achieved when the ker-nel has reached its maximum dryweight. A black layer forms at the tipof each kernel at physiological matu-rity. The average moisture of the ker-nel at this stage is 30 to 35 percent.Grain drying is a matter of physicalmoisture loss and varies with climaticconditions but should average at least0.5 percentage point per day.

Having a knowledge of the growthand development of the corn plantprovides the producer with a betterunderstanding of how different prob-lems and stresses affect final yield. Byunderstanding the effects that man-agement practices have during thevarious stages of corn development,the producer can manage the cornplant more intelligently so that it cannearly reach its yield potential.

8

Tillage SystemsLloyd Murdock and Ken Wells

Traditionally, tillage has been prac-ticed for the purpose of mixing sur-face residues deeper into the soil,loosening the soil prior to seedbedestablishment and to aid in weedcontrol. The primary tillage imple-ment for many years was the mold-board plow. The rough surface leftby primary tillage was smoothed bysecondary tillage implements, usu-ally a disk harrow followed by oneor more passes of another fine-toothed harrow for final smoothingof the surface in preparation forseeding. These techniques havebeen described as “conventional till-age.” Another traditional applica-tion of secondary tillage has beenthe use of a myriad of cultivatingtools to provide mechanical weedcontrol and to break up surfacecrusts. However, the advent of wide-spread use of chemical weed controlduring the late 1950s greatly re-duced the amount of secondary till-age used for weed control. Themajor disadvantages of these con-ventional tillage techniques wereincreased risk of soil erosion on slop-ing land and breakdown of soilstructure.

Largely due to massive nationwideloss of topsoil from conventional till-age, additional primary tillage tech-niques were developed to leave varyingamounts of the residues from the pre-vious crop lying on the soil surface forthe purpose of lowering the erosion po-tential. Several implements, mostly avariation of the chisel plow, were de-veloped to accomplish this. When fol-lowed by a shallow harrowing, theseconservation tillage techniques pro-vided a seedbed smooth enough forsuccessful planting of corn but still leftsome residue cover.

Further developments in chemicalweed control and planting equipmentthat could successfully plant throughsurface residues resulted in develop-ment of no-tillage seeding techniques.The only tillage involved in no-till-age seeding is the narrow, in-row dis-turbance made by the coulter andfurrow-opener on the planter. No-till-age results in most prior crop residuesremaining on the surface, whichcauses a dramatic reduction in soilerosion and increased water infiltra-tion. No-till techniques, pioneered byfarmers and researchers in Kentucky,are now so widely used in Kentuckythat they dominate seeding methodsfor corn and soybeans (Figure 1).When combined with other conser-vation tillage practices, greater use ofno-till has resulted in only a small per-centage of Kentucky’s corn and soy-bean crop being established byconventional techniques (Table 1).

No-tillage has a number of advan-tages, including less soil erosion ascompared with clean-tilled systems,and fuel, machinery, and time savingsare all impressive. There is also a ten-dency toward better crop yields onsoils that are moderately well drainedto well drained, due to higher water

capture and conservation often asso-ciated with the mulch of crop residuemaintained on the soil surface.

No-tillage is best suited to soils thatare moderately well drained to welldrained. The residue cover keeps soilscooler and wetter throughout muchof the growing season under no-tillconditions. This is particularly truewith heavy residue. Surface residuesthat leave somewhat poorly drainedsoils wetter can be an advantage dur-ing dry periods, but no-till plantingon such soils during cool, wet springscan cause delayed emergence and re-duced stands that reduce yields.

Management practices that can im-prove the performance of no-till cornin cool, wet conditions are the use ofin-row (pop-up) fertilizer (see fertilitysection) and row cleaners. The rowcleaners aid in warming and drying thesoil over the row, and the in-row fer-tilizer improves plant growth understress early in the season. Seed treat-ments that protect against root shootrots (Pythium ultimum) are quite help-ful and are often routinely added byseed companies.

Conservation tillage is a betterchoice for poorly drained soils. Thetilled surface allows these soils to

84 86 88 90Year

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Figure 1. Percent of Kentucky’s corn, soybean, and wheat acreage established with no-tilltechnology.

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warm and dry faster in the spring.However, conservation tillage prac-tices used on sloping fields that areprone to erosion should leave at least30 percent of the soil surface coveredby residue at planting to protect thefield from excessive erosion. This canbe done by reducing the amount ofsecondary tillage that is done on thefield. Secondary tillage is costly, timeconsuming, and frequently a majorculprit in causing soil compaction. Italso contributes to erosion, water pol-lution, and subsequent crop droughtstress. Protection against loss of top-soil is of much economic importance.Recent research by the University ofKentucky indicates that each inch oftopsoil on a Crider soil, up to the first8 inches, increases annual corn yieldby more than 10 bushels per acre.

Soil CompactionSoil compaction comes in a num-

ber of forms and from several causes,but in Kentucky the most commoncauses are either traffic or tillage whenthe soil is too wet. There is a watercontent at which any soil is most eas-ily compacted. In the words of one ex-pert, “This is when it is a little toowet to work, but I am going to do itanyway.”

Sidewall CompactionSidewall compaction can result

from planting a crop when the soil isa little too wet. This damaging effectcan be even greater on soils with arelatively high clay content at the sur-face. It occurs when the double discopener leaves the side wall of theplanting furrow smooth and com-pacted (slick as opposed to shattered)as it pushes the soil aside. The trail-ing press wheel then increases thecompaction with its downward force.If the soil stays very moist or wet, theroots may be able to penetrate thecompacted mud at the sidewall andexpand further into the soil. However,if the weather turns dry after plant-ing, the sidewalls then harden, androots are not able to push throughsince there are no pores or cracks. Thiscauses the roots to grow within theplanting furrow, along the directionof the row. Although plants may looknormal at emergence, they will beginto show nutrient and drought stressafter the corn is several inches high.This problem may be more commonin no-tillage because no-tillage soilshave better structure, and it is easierto traffic them in a wetter condition.The old adage of “waiting on no-till”is a good one. Sidewall compactioncan also occur with conventional till-age. If you can mold the soil into aball in your hand and the soil ball willnot easily crumble apart, it is too wetto plant.

Table 1. Tillage systems used for corn, soybean, and fall-seeded small grain in Kentucky,1998.1

Crop Total Acres

% Planted

No-TillConservation

Till2Conventional

Till3

Full Season Corn 1,345,000 51.8 34.5 13.7

Double Crop Corn 62,100 64.4 29.3 6.3

Full Season Soybeans 882,700 51.3 30.8 17.9

Double Crop Soybeans 474,700 86.7 12.4 0.9

Fall-Seeded Small Grains 603,000 24.6 62.0 13.4

All Crops 3,852,500 47.6 33.5 18.91 Conservation Technology Information Center data.2 Greater than 15 percent of residues left on surface.3 Fewer than 15 percent of residues left on surface.

Deeper CompactionWheel tracks on a wet field can also

contribute to a compaction problem.The trend to larger and heavier equip-ment means that axle weights haveincreased. A four-wheel drive tractor,a large combine with a full grain hop-per, a loaded manure wagon, a fertil-izer buggy or truck, or a loaded graincart can all exert great pressure on thesoil below the wheel. These weights,in combination with greater tire pres-sures, can compact the soil 12 to 18inches deep. When the degree of com-paction is sufficient to diminish porespace to the point that oxygen diffu-sion, water movement, and root pen-etration into and through the soil arerestricted, crop yields are likely to belowered.

Disc harrows are tillage tools thatcan cause severe compaction on wetsoils. The weight of a disc transmit-ted to the soil at the bottom edge ofeach blade creates enough pressure ina wet soil to compact a zone 4 to 6inches thick just below the disc blades.This is most common in disc-only till-age systems or where soils are exces-sively tilled and a disc is used whenthe soil is a little too wet.

How Common is Compaction inFields?

A survey of 175 fields in Kentuckyin 1992 and 1993 indicated that 46percent had no compaction, 18 per-cent were slightly compacted, 18 per-cent were moderately compacted, and18 percent were severely compacted.This survey used soil penetrometersto classify the amount of compaction.Limited research indicates that themoderate and severe categories shouldbe considered possible yield-limitingsituations. This means that about 30to 40 percent of Kentucky’s croppedfields are compacted enough to possi-bly limit the growth and yield of some

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crops. The more poorly drained fieldshad the most compaction, with 77percent of the poorly drained soils be-ing moderately or severely compacted,while only 20 percent of the well-drained soils were in this range. Whenthe primary tillage was discing, fieldswere twice as likely to have moderateor severe compaction as those wherea chisel or moldboard plow was used.The least likely fields to have com-paction were no-till fields.

When compaction was found, itwas most likely to begin at depths be-tween 6 and 9 inches and to termi-nate between 12 and 15 inches.However, compaction was found atother depths and depth thicknesses.

Effect of Compaction on YieldThe effect of compaction on yield

varies with the crop, weather condi-tions, and soil type. Corn is more sen-sitive to soil compaction than soybeanor wheat. Based on research in Ken-tucky and surrounding states, the es-timated yield reduction for corn is 30to 50 percent with extreme compac-tion such as that found under end rowsand at field entrances, 10 to 20 per-cent for fields with severe compaction,and 5 to 10 percent for those withmoderate compaction.

What to Do about CompactionThe best way to solve compaction

is to prevent it. Some simple thingscan make a difference.• Tire pressure is important. Lower

tire pressure increases the size ofthe tire print and lowers compac-tion. Many farmers carry 20 to 25psi in radial tires that are designedfor 7 to 12 psi. The proper tirepressure will not only reduce com-paction but will decrease slippageby 10 percent.

• Restrict heavy equipment (loadedgrain carts, trucks, etc.) to the small-est areas of the field as is possible.Use the same tracks with each passin the field, if possible.

• No-till means less compaction.There are fewer trips over the field,and the soil has better structure.This may not be evident until thefield has been no-tilled for three tofive years. By planting in the samerows each year, a controlled trafficpattern will result, restricting thewheel traffic to between certainrows.

• The most important managementpractice is to prevent traffic on wetsoils. Take soil from the tillage zoneand squeeze it in your hand. If thesoil ball cannot be easily crumbledapart, then the soil is too wet fortraffic.

How to Identify CompactionSometimes soils are deep-tilled

when there is no compaction. This iscostly and does not improve yields.The best way to identify compactionin a field is by using a soil penetrom-eter (soil compaction tester), a tilingrod, or a 3-ft length of 1/2- to 3/4-inchdiameter steel rod sharpened on oneend with a T-handle on the other end.These tools should be marked(notched) for depth and should onlybe used when the soil is at field ca-pacity after a rain (too wet to till, butnot sloppy muddy). This is best donein December through March whenthe profile is wet throughout. Underthese conditions, compacted layerscan be found and the depth and thick-ness of the compacted zone can beidentified. Each Cooperative Exten-sion Service office in Kentucky has asoil penetrometer with instructions onhow to use it and a form to record the

results. The form also has a methodto classify the amount and type of till-age found in the field. When readingsreach 300 pounds per square inch, thecompaction is considered root limit-ing. If one-third of the field has read-ings of 300 or more, a correctiveaction and change in tillage practicesshould be considered. When one-halfof the field has readings of 300 ormore, corrective action and changesin tillage practices definitely areneeded.

After moderate to severe compac-tion (lesser amounts of compactionare not harmful) has been identified,there is more than one way to correctit. When tillage or subsoiling is used,be sure the compacted zone is dryenough to shatter. Fall is generally thebest time because the subsoil is usu-ally drier and will shatter better. Thismeans that fields with identified prob-lems will be cropped for another sum-mer prior to compaction alleviation.Rotations to some other crops can alsohelp alleviate compaction. Alfalfa,sweet clover, and fescue all have rootsystems that are helpful but are ratherlong-term solutions.

SummaryCompaction can be caused by traf-

fic and some tillage operations andcan cause yield reductions in somecrops. The yield reduction may not beeasily seen unless the compaction isextreme. A lot of money is wasted ondeep tillage done in response to fearof compaction that does not exist.The key is using a total managementsystem that prevents compaction butalso monitors fields for the problemand then corrects it when and whereit is found.

11

Hybrid SelectionMorris Bitzer and James Herbek

One of the most important decisionsthat a producer must make when plan-ning for the next corn planting sea-son is what hybrid or hybrids to plant.Currently, most commercial corn pro-ducers plant single-cross hybrids, andmost of these hybrids are producedand marketed by private seed compa-nies. The corn producer’s challengeis to select those hybrids that are ap-propriate for each management situ-ation, keeping in mind the risksassociated with potential weather ex-tremes and field limitations. Manag-ing to get the highest possible yieldstarts with selecting those corn hy-brids that are best adapted to yourfarm and farming practices. Amongthe agronomic characteristics to con-sider in choosing hybrids are yield,maturity, standability, insect and dis-ease tolerance, seedling vigor, andstress tolerance.

YieldThe bottom line for most produc-

ers, all other things being equal, is touse the highest yielding hybrids avail-able. Under stress conditions, highyielding hybrids with superior stalkquality are most desirable. If a hybridcannot stand under stress conditions,lodging can severely decrease yields.State yield trial reports provide themost complete and unbiased informa-tion on the relationship between yieldand lodging. Most state trials are con-ducted at several locations under vary-ing degrees of stress conditions andinclude most of the hybrids sold in thestate. Each year, the University ofKentucky College of Agriculture con-ducts the Kentucky Hybrid Corn Per-formance Tests. This information ismade available both on a Web site andas a progress report available from yourcounty Cooperative Extension Ser-vice office.

The process of hybrid selectionshould consider the stability of per-formance across years and locations.Selection of more than one hybridwill reduce risk from weather and dis-ease. Each year several new hybridsare included in the test. Selecting newhybrids that are within one least stan-dard deviation (LSD) of the best hy-brids in the test will provide morechance of stability of performance. Inaddition to yield, data are presentedon moisture at harvest, percent stand,lodging, and test weight. Separatetables are presented on the protein,oil, and starch composition of thecorn hybrids.

Other good sources of informationabout hybrid performance are fromwell-managed local corn demonstra-tion plots sponsored by county Exten-sion groups, FFA chapters, and seedcorn companies. To be meaningful,these plots should have at least threereplications of each hybrid or a checkhybrid between plots of every two orthree hybrids with yield adjustmentsmade for location in the field. Manycorn companies today combine datafrom several locations, which does im-prove the reliability of the data. Striptest or plots with each hybrid enteredonly once are of little value for yieldcomparisons, as field variation is usu-ally greater than most differencesamong the hybrids.

MaturityChoosing the appropriate matu-

rity or maturities for each field, situ-ation, or farm operation is importantwhen selecting hybrids. The Ken-tucky Hybrid Corn Performance Testis a good source of information onrelative maturity of hybrids. The hy-brids are divided by maturity: early,medium, and late. Once you haveselected the desired maturity, you can

choose among the hybrids within amaturity group based on their perfor-mance characteristics.

Deciding which maturity or matu-rities to plant depends on a numberof factors that may be unique to eachfield or farm operation. In general,full-season hybrids (hybrids that usemost of the growing period in thatarea) produce the highest yields.However, recent hybrid developmenthas resulted in early and medium ma-turity hybrids having about the sameyield potential as the full-season hy-brids. Currently, the majority of thecorn grown in Kentucky is of mediummaturity. Early and medium maturityhybrids will have an earlier harvestand a lower moisture content thanlater maturing hybrids. Early maturityhybrids are useful for late plantings(after early June) because of theshorter growing season. Yield poten-tial of early maturity hybrids is com-parable to later maturity hybrids whenplanted at later planting dates with alower moisture content at harvest.Early and medium maturity hybridsare also a good choice for stress situa-tions, particularly soils with low wa-ter-holding capacity since they requireless moisture to mature.

Producers should plant several hy-brids differing in maturity, particularlyif a large acreage of corn is planted.Hybrids that differ in maturity reducethe risk of adverse weather (heat ordrought) and stress at pollination. Italso spreads the harvest period so corncan be harvested at optimal grainmoisture levels. The optimal propor-tion of different maturities differs foreach farm operation and depends onacreage, soil types, and other manage-ment factors. A typical recommenda-tion of different maturities might be10 to 15 percent early hybrids, 60 to70 percent medium hybrids, and 15to 20 percent late hybrids.

12

Growing Degree Days(GDD)

Most producers consider corn ma-turity as the number of calendar daysfrom planting to maturity. This sys-tem allows a farmer to compare thematurities between different hybridsbut does not necessarily indicate howmany days it will take for that hybridto reach physiological maturity. Thenumber of days that are required for ahybrid to reach maturity depends onlocation, date of planting, and theweather during the growing season. Ahybrid that is labeled as a 115 day hy-brid may take from 110 to 120 days tomature depending on the above fac-tors. This system of measuring cornmaturity does not take into accountthe complicated physiological pro-cesses that control growth and devel-opment of corn.

Each day that a corn plant growsfrom emergence to maturity does notcontribute equally to the develop-ment of the plant. Development isfaster during warmer days than it isduring cooler days. Although factorsother than temperature may enterinto determining rate of growth, thecorn industry adopted the GrowingDegree Days (GDD) system in 1970.This system uses a heat unit approachto the prediction of maturity that ismore accurate than the old days-to-maturity ratings and is based on thenumber of heat units necessary forcorn to reach physiological maturity.

Growing degree days are calculatedby subtracting the base temperature(50°F) from the average of the maxi-mum and minimum daily tempera-tures. Little or no corn plant growthoccurs when the temperature dropsbelow 50°F, and when the tempera-ture rises above 86°F development isreduced. Consequently, a GDD is cal-culated according to the followingequation:

Max Temp.(# 86º F) + Min Temp.

($ 50º F)2

GDD = - 50º F

The maximum temperature is thehighest temperature for the day (ad-justed downward to 86°F, if necessary),and the minimum temperature is thelowest for the day (adjusted upwardto 50°F, if necessary). For example, ifthe high temperature for the day is90°F and the minimum is 60°F, theGDD = (86 + 60)/2 - 50 = 23 for thatday. The University of Kentucky Ag-ricultural Weather Center (AWC)starts recording GDDs for corn onApril 1. These graphs are available atthe following URL:wwwagwx .ca .uky. edu /cg i -b in /cropdd_www.pl. By knowing theGDDs required for a particular hybridto mature, one can determine fromthe AWC when a particular hybridshould mature from the date that itemerged. For example, if the cornemerged on April 15 and required2,700 GDDs to mature, corn wouldreach physiological maturity about

August 26. This assumes fairly normalweather. The same site can also tellyou on August 26 how many GDDshas accumulated by that date. This in-formation can be used to determine ifa particular hybrid will mature beforethe average date of the first frost inthe fall.

Corn SeedHybrid seed corn is available in

different kernel sizes and shapes. Lo-cation on the ear influences the sizeand shape of the kernels. Large roundseed comes from the base of the ear;small round seed, from the tip; and flatseed, from the center of the ear. Thekey to accurate planting is to selectkernel size and shape to fit their plant-ing equipment. For plateless-typeplanters that use vacuum or air pres-sure to hold seed to a plate or drum orfinger pickup units, seed size andshape are not as important. Thesetypes of planting units can use differ-ent seed sizes and shapes.

Research has not found any rela-tionship between kernel size or shapeand emergence on yield. Thus, withina given hybrid, seed of any size orshape has the same genetic potential.Growers with plateless planters cantake advantage of lower prices oftenassociated with less popular seed sizesand shapes. Corn hybrids should beselected on the basis of their agro-nomic performance, not on their ker-nel size or shape, if the plantingequipment is suitable.

The following equation can be usedto determine the number of live plantsthat can be expected from corn seedat a given seeding rate:

It is fairly common to find that asmany as 10 to 15 percent of the seedsplanted do not produce a live plantunder field conditions.

100% pure seed

100% germination

xseeding rate x

Expected stand =

13

Impact of BiotechnologyRic Bessin

Agricultural biotech crops on themarket today have been given genetictraits from other organisms to provideprotection from pests and toleranceto pesticides or to improve food andfeed quality. To transform a plant, thegene that produces the trait of inter-est is identified and separated from therest of the genetic material in a do-nor organism. Most organisms havethousands of genes, and a single generepresents only a tiny fraction of thetotal genetic makeup of an organism.A donor organism may be a bacte-rium, fungus, or even another plantspecies. In the case of Bt corn, thedonor organism was a naturally occur-ring soil bacterium, Bacillusthuringiensis, and the gene of interestproduces a protein that kills Lepi-doptera larvae, in particular, European

corn borer. The donor gene along witha genetic promoter (which turns thegene on in the corn plant) and a ge-netic marker (which allows plantsbreeders to quickly identify trans-formed plants) were inserted into cornembryos. These new genes are thenincorporated into commercial cornhybrids using traditional backcrossingbreeding methods.

Plants produced through biotech-nology are closely regulated by theUSDA APHIS, the EPA, and theFDA. Producers should not select ahybrid based solely on the fact that itis biotechnology derived. Selection ofa biotechnologically derived hybridfor pest-resistant traits should dependon whether the resistant traits areneeded. Likewise, selection ofbiotechnologically derived hybrids

with improved food or feed qualityshould depend on market value andprofit potential.

Producers wanting to use agbiotech hybrids should always checkwith their grain buyers prior to seedpurchase to be certain that these hy-brids are approved and will be ac-cepted at the market. Some biotechcrops have not been approved or ac-cepted in certain markets. The recallof foods containing traces of StarLinkcorn taught us an important lessonthat the utmost care must be taken toprevent commingling of grain in-tended for different markets. Becausecorn is pollinated with wind-blownpollen, field isolation of up to 660 feetmay be needed to prevent cross-pol-lination between different hybrids toensure product identity.

14

Planting PracticesMorris Bitzer and James Herbek

Planting DatePlanting corn early in Kentucky is

not as important as it is in states far-ther north. Kentucky’s growing seasonis long enough that corn may beplanted from early April to mid-Mayin most years and still obtain highyields. Optimal planting dates usuallyrange from April 1 to May 1 in West-ern Kentucky and April 15 to May 15in Central and Eastern Kentucky. Insome years, corn is planted in March,but often it must be replanted becauseof poor stands due to cold soil. Themost critical factor in determiningwhen to start planting corn is the soiltemperature. Planting when soil tem-peratures are above 50°F at a 2-inchdepth for three or four days appears tobe an excellent guide. A soil tempera-ture of 50°F at 7:00 a.m. or 55°F at 1:00p.m. should assure that temperaturesare suitable for germination and growthfor at least several hours during the day.Because of residue cover, soils for no-tillage planting usually do not warm upas early as tilled soils. If using no-till,planting may have to be delayed byfour to seven days.

Earlier planted corn has usuallyhad fewer insect and disease prob-lems. For maximum yields, cornshould be planted before May 1 inextreme Western Kentucky, by May10 in west-central Kentucky, and byMay 15 in Eastern Kentucky. If cornplanting is delayed past June 5, anearlier-maturing hybrid should beplanted. Several years of researchhave shown that a 1 percent per dayyield loss can be expected in cornplanted after May 10-15.

Planting DepthThe speed of germination and uni-

formity of plant emergence dependnot only on soil temperature but alsoon planting depth. Under good con-ditions of temperature and moisture,

a 11/2- to 2-inch depth is ideal. Someresearch in the Midwest has shownthat 2 inches is the best depth forhighest yields. For early planting, es-pecially when the soil is cooler, plantat a slightly shallower depth of 1 to 11/2 inches. If the soil is dry, which issometimes the case when plantinglate, you may need to plant 2 1/2 to 3inches deep to get the seed to mois-ture. Soil temperatures in the upper 2inches are greatly influenced by airtemperature and solar radiation andcan fluctuate as much as 10°F duringa single day.

Planting too deep or too shallowcan adversely affect corn performance.Early in the season, soils are colder atdeeper depths and may slow germina-tion and subject the seed to diseaseor insect injury. A seed treatment forinsects is recommended with earlyplanting. Planting depths greater than2 inches may result in seedlings withless vigor, slower growth and devel-opment and lower yield. Planting cornseeds too deep can result in the co-leoptile growth ceasing below the soilsurface leaving the tender shoot togrow unprotected toward the soil sur-face. An unprotected shoot would bedamaged and leaves unfurled beforeit emerges. Planting depths over 3inches should not be considered un-der any soil conditions because ofemergence problems. Conversely,planting too shallow can lead to poornodal root development, shallowrooting depth, and poor drought tol-erance. Do not plant less than 1 inchdeep under any circumstances becausepoor nodal root development (perma-nent root system) may occur, whichcan result in plants falling over,known as suicidal corn.

Depth is particularly critical in no-tillage planting. For germination tooccur rapidly and uniformly, the seedmust be at a uniform depth and sur-rounded by soil. Some types of seed

firmers may improve uniform plant-ing depth. Careful control of plant-ing depth improves stands anduniform emergence.

Plant PopulationsThe optimum plant population de-

pends on the yield level that a particu-lar environment (soil, moisture)permits. Average corn plant popula-tions have gradually increased over theyears as have corn yields. These in-creases can be attributed to improve-ments in production technology as wellas genetic improvement in yield poten-tial, standability, and stress tolerance.Today’s corn hybrids have higher yieldpotentials because of greater yield sta-bility over a wider range of environ-ments, superior stalk strength andstandability, and better tolerate com-petitive stress (less barrenness) at highplant densities than previous hybrids.If a stressful environment occurs un-der recommended high populationswith modern-day hybrids, extremelyhigh yields will not occur, but, it is lesslikely that a significant yield decreasewill occur unless the population hasgreatly exceeded the recommended op-timum range.

Recent studies at the University ofKentucky have shown trends formaximum yields at higher plant popu-lations. In the 3 year study (Table 1),corn yields increased significantly ateach increased level of plant popula-tion. In the 2-year study with twohybrids (Table 2), there were no sig-nificant increases in yields with in-creased plant populations; however,there was a trend toward slightlyhigher yields at 28,000 plants per acre.

Corn can compensate for low popu-lations by producing larger ears or ad-ditional ears. However, most hybridstoday produce only one ear. Hybridsalso respond differently to plant popu-lations. When the population is toohigh, some hybrids may have barren

15

stalks and lodging potential tends toincrease. Consult seed company rec-ommendations for desired plant popu-lations of specific hybrids.

Using the data from Tables 1 and2 and data collected by R. Barnhisel,University of Kentucky AgronomyDepartment, during the last five yearsof variable rate seeding studies, therecommended corn seeding rates forKentucky are presented in Table 3.Corn planted on low yielding soilsshould not be seeded above 22,000seeds per acre, and on high yielding,uniform soils, top yields are obtainedwith seeding rates of 28,000 to 30,000seeds per acre. For intermediate yields(120 to 175 bushels per acre), use in-termediate populations. Many timesyields close to 200 bushels per acre canbe achieved at 26,000 to 28,000 seedsper acre. Excessive populations canlead to more lodging, more diseasepressure, and lower yields in mostyears. The final population should beapproximately 85 to 90 percent of theseeding rate as shown in Table 4.

Row WidthStudies in Kentucky during the

1970s and 1980s showed no advan-tage in yield for corn planted in rowsnarrower than 36 inches. However, bythe early 1990s, a large percentage ofthe corn was grown in 30-inch rowsbecause producers had switched tonarrower rows for soybean and wereusing the same equipment for corn.In the early 1990s, much interest wasgenerated for using 20-inch rows forcorn. However, research from most ofthe states surrounding Kentucky didnot show any advantage for 20-inchrows over 30-inch rows. Research wasstarted in the mid-1990s comparing20-inch, 30-inch, and 36-inch rowwidth for corn in Kentucky (Table 1).These data showed an advantage for30-inch over 36-inch row widths butthat there was no advantage for 20-inch rows over 30-inch rows. Actu-ally, 20-inch rows were no better than36-inch rows. In Table 2, two moreyears of research on row width gave

the same results. Consequently, therecommended row width for corn pro-duction in Kentucky is 30-inch rows.

Any consideration for a change inrow spacing must take into accountthe economic return of that change.Most economic analysis comparisonsindicate that a yield increase of at least6 to 8 percent on large acreages (>500acres) over a seven to 10 year periodis needed to cover expenses incurredwhen switching row widths unlessnew equipment is needed to replaceold equipment.

Replanting CornIf a corn crop has been damaged or

the stand is poor early enough to con-sider replanting, there are several fac-tors that need to be considered. Some

Table 1. Effect of plant population and rowwidth on corn yields in Kentucky (eight-location average, 1995-97). Bitzer andHerbek.

TreatmentYield

(bu/ac)

Plant population 22,000 164a*

(Plants/acre) 26,000 171b

30,000 178c

Row width 20 inch 170b

30 inch 175a

36 inch 169b

*Means followed by different letters aresignificantly different at 0.05 level ofsignificance.

Table 2. Effect of plant population and rowwidth on corn yields in Kentucky (four-location average, 1998-99).

Treatment

Yield (bu/ac)

1998 1999 Ave.

Plantpopulation

24,000 167 130 149*

(Plants/acre) 28,000 174 129 152

32,000 172 126 149

Row width 20 inch 171 126 148

30 inch 171 131 151

* There were no significant differencesamong means at 0.05 level of significance.

of these factors are seeding rate andexpected plant stand, plant stand af-ter damage or loss of stand, uniformityof plant stand being considered, re-planting date and seed costs to re-plant, and potential pest problemswith replanted corn. Whether to re-plant or not comes down to decidingwhether the replant-crop yields wouldbe sufficient to cover the costs of re-planting and net enough to make itworth the effort. The key factor toconsider is found in Table 5. This tablewill help you decide if replanting willyield more corn than leaving thepresent stand. The information in thistable was obtained and adapted fromthe National Corn Handbook, NCH-30, “Guidelines for Making Corn Re-planting Decisions.” Refer to this

Table 3. Recommended cornseeding rates for Kentucky.

Seeding rate*(seeds/acre)

Grain 22,000 - 30,000

Silage 24,000 - 30,000

Irrigated 26,000 - 32,000

* Range depends on potentialyield of soil ranging from lessthan 100 bu/ac for the lowrange to more than 200 bu/acfor the high range.

Table 4. Corn population planting guide.

Harvestpopulation1

Requiredplanting rate

Inches between kernelswhen planting at

various row widths

20" 30" 36" 38"

16,200 18,000 17.4 11.7 9.7 9.2

17,100 19,000 16.5 11.1 9.2 8.7

18,000 20,000 15.7 10.5 8.7 8.3

19,800 22,000 14.3 9.5 7.9 7.5

21,600 24,000 13.1 8.7 7.2 6.9

23,500 26,000 12.1 8.1 6.7 6.4

25,200 28,000 11.2 7.5 6.2 5.9

27,000 30,000 10.5 7.0 5.8 5.5

28,800 32,000 9.8 6.5 5.4 5.21 Allows 10 percent stand loss.

16

Cropping Rotation BenefitsMorris Bitzer and James Herbek

There are many cropping sequencesthat can be used for growing corn inKentucky. Economically and agro-nomically, it is difficult to justify grow-ing corn in a monoculture instead ofusing a rotation. Data from many stateshave shown that a yield loss up to 10percent occurs when corn is grown twoor more years in succession. Most ofthat loss occurs in the second year.

There are several benefits fromgrowing corn in rotation. With lesspressure from disease, insects, andweeds, production costs are lower andprofits are higher due to higher cornyields. Rotation studies in Kentuckyhave shown a yield increase of about10 bushels per acre for corn grown ina rotation with soybean or soybeanand wheat. Rotations also improve

Table 5. Grain yields for various planting dates and population rates, expressed as a percentof optimum planting date and population rate (uniformly spaced within row).

Planting date

Plants per acre at harvest

12,000 14,000 16,000 18,000 20,000 22,500 25,000

(% of optimum yield)

April 15 70 76 81 85 88 91 93

April 20 72 78 83 87 90 93 95

April 25 75 81 86 90 93 96 98

May 1 77 83 88 92 95 98 100

May 6 78 83 88 92 95 98 100

May 11 77 83 88 92 95 98 99

May 16 75 81 86 90 93 96 98

May 21 73 78 83 87 91 94 95

May 26 69 75 80 84 87 90 92

May 31 64 70 75 79 82 85 87

June 5 59 64 69 73 77 80 81

June 10 52 58 63 67 70 73 75

publication for a much more detailedexplanation of making a replantingdecision, or contact your state cornspecialist.

Table 5 contains the percentage ofexpected corn yield for planting dateand harvest populations. Optimumpopulation is considered to be 25,000plants per acre with the optimumplanting date to be the first week to 10days of May. Information in this tablealong with consideration of the above-mentioned factors should aid in mak-ing a replanting decision. To use thistable, consider this example: Supposea field was planted on May 1 with anexpected harvest population of 25,000plants per acre. Later, the stand was re-duced to 14,000 plants per acre; theyield loss penalty for the reduced popu-lation would be 17 percent (100 per-cent minus 83 percent). If it wasdecided to replant the field on May 21to obtain a desired population of25,000 plants per acre, a yield of 95percent of optimum could be expected;for a net gain of 12 percent (95 per-cent minus 83 percent). Thus, replant-

ing should be profitable in this case.However, if the stand was reduced to16,000 plants per acre on May 31, adecision to replant would not be prof-itable, as an expected yield of only 87percent would be realized as comparedto an 88 percent yield if the stand wasleft standing. This is simply a guide tohelp you make a decision concerningreplanting. Table 5 takes into account

the loss of yield at later plantings butdoes not take into account non-uni-form stands. All these factors must beweighed against expected replantingyield gains. If after considering all thefactors, there is still doubt as to whethera field should be replanted, it will prob-ably be correct more often if the fieldis left as is.

the use and availability of nutrients,and with the proper selection of a ro-tation crop, the productivity of thecomplete cropping system. Corn fitswell into most crop rotations. Thecorn/soybean or corn/wheat/double-cropped soybean (three crops in twoyears) cropping sequences are com-monly used in Kentucky.

17

Fertility ManagementLloyd Murdock

IntroductionThe purpose of developing a fertil-

ity program is to ensure that adequatelevels of nutrients are available forplant uptake in support of the yieldpotential for the climatic, plant ge-netic, and soil environmental factorsimpacting plant growth in any givenfield. A regular soil sampling programis the best way to obtain the informa-tion necessary to develop such a fer-tility program. An occasional tissuesampling program helps augment thesoil sampling program. For corn pro-duction, nutrient application mostcommonly involves lime for pH, aswell as nitrogen (N), phosphorus (P),and potassium (K). Zinc (Zn) or mag-nesium (Mg) is needed occasionally.In rare cases, boron (B) may be nec-essary.

Soil SamplingWhen you take soil test samples,

keep in mind that a few ounces of soilare being tested to determine lime andfertilizer needs for millions of poundsof soil in the field. It is absolutely nec-essary that the soil sample you sendto the laboratory accurately representthe area sampled.

Soil samples can be collected dur-ing much of the year, although Sep-tember to December or February toApril are the best times. There willbe a small difference in soil test re-sults depending on the time of theyear of sampling. So, once a time ofthe year is selected, always sample inthe same season.

How to SampleA soil probe, auger, garden trowel,

or a spade and knife are all the toolsyou need to take the individual coresthat will make up the field sample. Youwill also need a clean, dry bucket(preferably plastic) to collect and mixthe sample cores. Soil sample boxes

or bags and information forms for sub-mitting samples are available at allcounty Cooperative Extension ser-vices offices.

The most representative samplecan be obtained from a large field bysampling smaller, more uniform areason the basis of soil type, cropping his-tory, erosion, or past managementpractices. A sample should representno more than 20 acres except whensoils, past management, and croppinghistory are quite uniform. Whentroubleshooting problem areas infields during the growing season, takea sample from the problem area andadjacent areas with good crop growth.

Collect at least 10 soil cores insmall areas and up to 30 cores in largerfields. Take the soil cores randomlythroughout the area to be sampled andplace in the bucket.

Tilled areas—Take soil cores to thedepth of the tillage operation (usuallyabout 6 inches).

No-tilled areas—Take soil cores toa depth of 4 inches where fertilizer orlime remains on the soil surface or isincorporated only in the surface 1 to2 inches.

Lime and fertilizer applied continu-ously to the surface of no-till fields re-sults in a build-up of immobilenutrients within the top 1 to 3 inchesof the field, with little effect on in-creasing soil test values below thisdepth. This stratification of P, K, Ca,and Mg has not been a problem in no-till corn production in Kentucky, butno-till fields are sampled to a 4-inchdepth because of nutrient stratifica-tion. Also, if most or all of the N isapplied on the soil surface, continu-ous no-tillage does cause increasedacidity in the top 1 to 2 inches of soil.This surface acidity reduces the activ-ity of some herbicides, particularly thetriazines. This surface acidity mayneed occasional monitoring with aseparate 2-inch soil sampling.

Certain areas should be avoidedwhen taking soil samples. Do not in-clude soil from the following areas:• Backfurrows or dead furrows.• Old fencerows.• Near or in rows where banded fer-

tilizer was applied.• Areas used for manure or hay stor-

age or livestock feeding.• Highly eroded areas.

Sampling for Precision AgricultureMany farmers now sample fields to

delineate soil-test variability so thatthey can make variable-rate applica-tions of lime and fertilizer within thefield. This is most commonly done bysampling fields on a grid. Grid sam-pling involves establishing some mea-sured grid intersects within a field andthen taking a composite soil samplewithin a small area either around thegrid intersects or from the center ofthe grid. The question of concern iswhat grid size to use. A widely usedmethod is to grid fields into 330- x330-foot (2.5 acre) blocks and sampleeach block by compositing six or eightcores taken within a 60-foot radius ofthe center of the block. While suchregimented grid sampling gives a bet-ter picture of soil-test variabilitywithin a field, it does require more in-tensive sampling, which increasescosts. Research on grid size has shownthat the smaller the grid, the more ac-curate the map of a field’s availabil-ity. Grids on 100-foot intersects (0.23acre per grid) are much more accu-rate than 330-foot intersect grids, butthey require the expense of a soil testfor every 0.23 acre in a field.

The expense of the large numberof soil tests required by grid samplinghas resulted in some farmers resortingto a procedure presently called “smartsampling.” This procedure is identi-cal to the long-standing University ofKentucky recommendation of (a)sampling fields in units no larger than

18

20 acres and (b) separately samplingareas known to be different within thefield. Currently, “smart sampling” pro-tocols are derived from field maps ofcrop yield made with yield monitors,where low-producing areas are iden-tified and then sampled separately.

Sample PreparationAfter all cores are collected and

placed in the bucket, crush the soilmaterial and mix the sample thor-oughly by hand. Take about a pintvolume from the bucket and allow itto air dry in an open space free fromcontamination. Do not dry the samplein an oven or at an abnormally hightemperature.

Soil TestingExtractants. Soil pH is nearly al-

ways measured on a slurry of soil anddistilled water or a buffer solution, butnutrient measurements are made af-ter their extraction from the soil. Dif-ferent laboratories may use differentextractants or extraction procedures.The most commonly used extractantsare:1. Mehlich-3—used by the UK Soil

Testing Lab and widely used byother testing labs.

2. Mehlich-1—widely used in theSoutheast.

3. Bray-1 and neutral, normal, am-monium acetate—widely used inthe Midwest.The ultimate concern is that fer-

tilizer nutrients be recommended onthe basis of crop response that hasbeen correlated with, and calibratedfor, each specific extractant. For ex-ample, UK’s fertilizer recommenda-tions are correlated and calibrated forsoil test values determined with theMehlich-3 extractant. Using UK’srecommendations for soil test valuesdetermined with the Mehlich-1 ex-tractant would be totally invalid andmight result in fertilizer rate recom-mendations that are much greaterthan needed.

Soil Test Results—UnitsSome laboratories report results in

parts per million (ppm), while othersreport in pounds per acre. If there isneed to convert from one to the other,use the following formulas to estimatethis comparison:

ppm x 2 = lbs per acrelbs per acre ) 2 = ppm

FertilizerRecommendations

It is not uncommon for a farmer toreceive vastly different fertilizer rec-ommendations after splitting a soilsample and sending half to differentlabs. Such differences are due to thediffering philosophies used in inter-preting soil test values and making fer-tilizer recommendations.

Several different philosophies areused in Kentucky, depending on whois making the recommendation. Farmsupply dealers, agricultural consult-ants, and soil test laboratories use dif-ferent approaches. Philosophiescommonly used in making recom-mendations are discussed below. Eachof these philosophies is based on dif-ferent assumptions about crop needsand how crops respond to appliednutrition at different soil test levelsand to different amounts and ratiosof available nutrients. For any of thesephilosophies to have value in Ken-tucky, they must be correlated to thesoil types and climatic conditions ofKentucky.

Crop SufficiencyThe crop response is the focus of this

philosophy. The expected response ofthe crop at any given soil test level iswhat determines the fertilizer rate rec-ommended for each nutrient. Theamount of fertilizer recommended isdetermined from many field trials ondifferent soils over many years. The ap-proach is based on research data thatadequately predict a crop response un-der normal to good conditions.

Nutrient BalanceThe theory behind this philosophy

is that the correct nutrient balanceresults in maximum crop response.This approach is often adopted whenwide extremes in soil type are encoun-tered or when the research base forthe soil types encountered is limited.

Maintenance FertilizationAccording to this philosophy, the

nutrients removed at harvest shouldalways be replaced. This approach isused especially on soils that test me-dium to high in P and K. This methodis often used in combination with arecommendation made by either thenutrient balance or crop sufficiencyapproaches, which use a soil test as abasis for recommendation. A yieldresponse to this extra maintenancefertilizer is usually not expected, butthe fertilizer is added to maintain soiltest levels over time.

Secondary Nutrients andMicronutrients by Soil Testing

This concept is based on testing thesoil for secondary nutrients and micro-nutrients, and recommendations aremade based only on this information,regardless of whether the correlationand calibration research base exists.Using a soil test in this way greatly in-creases the chance of adding a nutri-ent where it may not be needed. Thisis significantly different from makingrecommendations for these nutrientswhen both tissue and soil tests are usedto determine deficiency or when anarea or soil type is known to have aconsistent secondary nutrient or mi-cronutrient problem.

Combination ofPhilosophies

Normally recommendations aremade from a combination of thesephilosophies. The philosophy thatusually stands alone is the crop suffi-ciency philosophy. The maintenancephilosophy frequently is used with ei-

19

ther the sufficiency or the nutrientbalance approaches. The philosophyof recommending micronutrientsbased only on a soil test is sometimesused with all approaches but is mostcommonly used with the maintenanceand nutrient balance philosophies.

Summary of FertilizerRecommendationPhilosophies

All of these philosophies or combi-nations of philosophies have beenevaluated in Kentucky. All resulted inexcellent crop yields when the weatherconditions were good. In almost allcases, there was no real difference inyields. However, there were alwaysfairly large differences in the amountand kinds of fertilizer recommended.This resulted in large differences in thecosts, with very high fertilizer costs giv-ing no yield advantage. Fertilizer ratesbased on the crop sufficiency philoso-phy usually cost the least and produceyields equivalent to the more costlyrecommendations derived from theother philosophies tested. Soil teststaken a few years following the appli-cation of the various recommendationsindicated that surplus fertilizer was be-ing stored in the soil.

LimingCauses of Acidity

Greater soil acidity is the result ofnaturally occurring processes, mostlythe decomposition of soil organic mat-ter and plant residues and the removalof bases from the soil. Acid-formingfertilizers accelerate the formation ofacidity, and the “salt” effect from fer-tilizer use also increases soil acidity.

The commonly used N fertilizersare the most usual source of acid-form-ing fertilizers. When used at high ratesfor a number of years, these N fertiliz-ers cause the soil pH to drop rapidly.Table 1 shows the amounts of limeneeded to neutralize acidity from vari-ous N fertilizers.

Measuring AciditySoils that contain

higher levels of activehydrogen and alumi-num or both in relationto Ca and Mg areacidic. The degree ofacidity is expressed interms of pH. A pH of 7is neutral; pH valuesbelow 7 are acidic, andthose above 7 are alka-line. Each pH unit represents a 10-foldchange in acidity. For example, a soilwith pH 5 has 10 times more activeacidity than one with pH 6. Most cropsgrow best at soil pH values between 6and 7.

The pH of the soil is a measure-ment made on a slurry of soil and wa-ter. It is a measure of the acidity inthe soil solution that is in contactwith plant roots. The soil buffer pH isa measure of reserve soil acidity thatis held on the surface of soil mineraland organic particles and that mustalso be neutralized in order to increasethe soil pH. In the soil buffer test, abuffer solution is mixed with soil, andthe pH of the slurry is measured. Theresult from the buffer test is reportedas buffer pH. The buffer pH is usedonly to determine lime requirements.The buffer pH and the soil pH to-gether can be used to determine thelime required to change soil pH tosome desired level.

Symptoms of Acidity and Benefitsof Liming

Lime neutralizes soil acidity, raisessoil pH, and adds Ca and Mg to thesoil. The range in soil pH for optimalnutrient availability is generally be-tween 6 and 7, with a target pH ofabout 6.5. Outside this range, one ormore nutrients may become deficient.Liming acid soils also improves the en-vironment for beneficial soil micro-organisms and promotes a more rapidbreakdown of soil organic matter, re-leasing nutrients for growing plants.

Corn is somewhat less sensitive toacid soils than wheat and soybeanwith which it is usually rotated. Nev-

Table 1. Approximate pounds of ag lime needed to neutralizethe acidity generated by nitrogen fertilizers.

Pure product

Lime needed for 1 lb ofactual N added

% N100% pure

fine limeNormalag lime

Ammonium Nitrate 34 1.8 2.7

Urea 46 1.8 2.7

Anhydrous Ammonia 82.5 1.8 2.7

N Solutions 28-32 1.8 2.7

Ammonium Sulfate 21 5.3 7.9

Diammonium Phosphate 18 1.8 2.7

ertheless, at very low pH, corn suffersfrom both manganese and aluminumtoxicity. Manganese toxicity causesstriped leaves and stunted growth, andmany times there is a string of necroticspots on the interveins of the leaves.Aluminum toxicity results in poorroot growth that causes short thickroots with few fine roots, which re-sults in drought injury. Both symptomsare common in soils with pH valuesof 4 to 5.2; yields are often greatly re-duced, and many nutrients are ren-dered much less available for plantuptake. This is especially true forphosphorus but also the availabilityof calcium, magnesium, nitrogen, sul-fur, potassium, and molybdenum (seeFigure 1).

Between pH 5 and 5.5, no visualsymptoms are likely, and plant growthmay appear normal, but yield willprobably be reduced by 10 percent ormore. The nutrients listed above aremore available than at a pH below 5but are still reduced in availability.The efficiency of most added fertiliz-ers, especially P, will be reduced. Fer-tilizer P efficiency will probably bereduced by 25 percent or more whencompared to pH 6.5.

Corn grows well with little or noyield reduction between pH 5.5 and6.0, but fertilizer efficiency is still re-duced. The reduction in the availabil-ity of P will be in the 0 to 25 percentrange when compared to pH 6.5.

Although corn can tolerate mod-erately acid soils, growers need to keeptwo points in mind. First, addingammonical N fertilizer to corn greatlyaccelerates soil acidification. Second,in no-till corn fields where most of the

20

mesh screen and at least 35 percentwill pass a 50-mesh screen. This is aminimum standard for the lime to beeffective in neutralizing soil acidity.

Relative neutralizing value (RNV)estimates the percent of agriculturallime that will dissolve in a three- tofour-year period. The higher the RNV,the higher the lime’s quality. Limewhose RNV is 80 will require a smalleramount to reach a desired pH thanone whose RNV is 60. The averageRNV in Kentucky is about 67, andthis is the basis for University o fKentucky’s lime rate recommenda-tions. County Extension agents haveinformation on the RNV levels forsources of agricultural lime being soldin Kentucky.

Other liming materials are some-times available in an area. These areusually by-products of industry or areliquid suspensions of finely groundlimestone. Use of these materialsshould be based on their purity (ex-pressed as percent CaCO3) and fine-ness. With suspensions, the actualamount of lime in the mix determinesthe liming value. For example, a tonof lime suspension may contain only1,000 pounds of lime. The rest is wa-ter and suspension agent. Specialtyproducts like bagged, finely groundlimestone, pelletized lime, hydratedlime, ground oyster shells, and others

are available. These are usually moreexpensive but are convenient to useon small areas. Be careful in usingthese products so that an area is notover-limed.

Lime RatesWhen cornfields are limed, enough

should be used to raise the soil pH tothe mid-6 range (pH 6.2 to 6.4 is sug-gested by the University of Ken-tucky). The exact amount needed islargely due to the amount of reserveacidity that is held on the soil particlesurface as measured by the buffer pH.By knowing the buffer pH togetherwith water pH, the amount of ag limenecessary to raise the soil to pH 6.4can be determined. The rates can befound in the Extension publicationLime and Fertilizer Recommendations(AGR-1).

The adjustment of soil pH by limeis affected by five factors:1. Thoroughness of mixing into the

soil.2. Depth of mixing into soil (top 6

inches is assumed except in no-tillsoils).

3. Time of reaction (four years isneeded for complete reaction ofagricultural lime, but the reactiontime for hydrated lime is muchshorter).

4. Quality of agricultural lime (anRNV of 67 is assumed).

5. Continued use of acid-forming Nfertilizers, which can lower the fi-nal soil pH obtained.When applying lime rates greater

than 4 tons per acre, the lime shouldbe thoroughly mixed in the plow layerby applying one-half the recom-mended rate before plowing and theother half after plowing, followed bydisking.

When to LimeLime can be applied at any time.

With adequate soil incorporation andmoisture, a measurable pH change canoccur within 4 weeks. However, ittakes six to 12 months for a signifi-cant amount of the lime to dissolveand make the desired change in soil

N is added to the soil surface, the soilsurface can become very acid (belowpH 5) within three to four years. Oncethis happens, toxic amounts of alumi-num and manganese are produced,and the triazine herbicides (atrazineand simazine) are rapidly degradedand do not provide adequate weedcontrol.

At pH 7.0 or above, manganeseand zinc may become deficient. Forexample, zinc deficiency of corn hasbeen observed in Kentucky soils atthese pH levels, especially when avail-able P is also high.

The best liming program for corninvolves a soil test every two years andlime applied according to soil test rec-ommendations. On the average, onecan expect the need for about one-half ton of lime per acre per year, butthis is usually added at a rate of 2 to 3tons per acre every three to six years.

Lime SourcesThe most important source of lime

for agricultural use is ground lime-stone called agricultural lime. Thequality of agricultural lime is deter-mined by its purity and fineness ofgrind. The Kentucky lime law speci-fies that agricultural lime must be 80percent pure (calcium carbonateequivalence) and must be ground fineenough that 90 percent will pass a 10-

Figure 1. Symptoms of corn growing in low pH soils.

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pH. For this reason, lime should beapplied at least six months before thetarget crop is to be planted. Fall is agood time to apply lime so dissolutioncan occur during the winter. Also, fallweather is usually better for getting onthe land with spreading equipment.

Nitrogen

Importance of NNitrogen is the fertilizer element

required in the largest amounts, andat the greatest cost, for corn produc-tion. Each bushel of grain harvestedwill contain almost a pound of N.Properly fertilized silage corn removesslightly more than 10 pounds of N foreach 1,000 pounds of dry matter.Availability of N in most soils is toolow to supply all the N required foroptimal corn production without fer-tilizer N. Recommended rates takeinto account that only one-third totwo-thirds of the fertilizer N added isrecovered in the harvested corn.

Nitrogen recovery is variable andlargely unpredictable. This is prima-rily due to the powerful effect ofweather on the release of native soilN and on the fate of fertilizer N. Thismakes it impossible to precisely pre-dict the quantity of N required formaximum yield or maximum eco-nomic return and is the reason thatmeaningful soil tests for N availabil-ity are not very useful for most situa-tions in Kentucky.

Neither the amount of organicmatter nor the amount of soil nitratehas proven to be a reliable indicatorof the available N for field cropsgrown under Kentucky conditions.For this reason, N recommendationsfor field crops are based on past crop-ping history, soil management, andsoil properties.

Deficiency SymptomsYoung corn plants show a general

chlorosis or yellowing of the entireplant when N is limiting. Under severeearly growth deficiency, the bottomleaves may “fire” and desiccate. If N

supply becomes limiting after stalkelongation begins, through the remain-der of the growing season N is translo-cated from the most mature leaves atthe lower stalk positions to the newerleaves or the ear. This causes the lowerleaves to show a characteristic “V”-shaped yellowing extending from theleaf tip along the midrib toward thestalk, with the open end of the “V” atthe leaf tip. The effect on growth andgrain yield can range from stunted,chlorotic plants, which may not evenform an ear, to normal-appearing plantswith ears that do not have fully formedkernels toward the tips of the ears (seeFigure 2).

Time of Rapid N Uptake andPartitioning

The absolute amount of N neededduring the first few weeks of growth issmall and uptake is slow. Uptake pro-gressively increases as the plant becomeslarger with rapid uptake of N beginningabout 3 weeks before tasseling. Most ofthe N taken up will be held in the leavesuntil grain formation begins. After grainformation begins, there is translocationof much N from other plant parts to theear. About half the total N uptake oc-curs by the time of pollination.

Factors Affecting NitrogenAvailability

Organic soil N is found in largequantities in virtually all soils. A soilthat has 3 percent organic matter con-tains more than 3,000 pounds of or-ganic N per acre. However, only asmall part of this, 1 to 5 percent eachseason, is broken down to inorganicN forms that are available to plants.A greater rate of N release can be ex-pected from fresh plant residues andfrom plowed-down or killed grass andlegume sods. For this reason, croppinghistory is an important considerationwhen estimating fertilizer require-ments. Inorganic ammonium (NH4

+)is either released by organic matter de-composition or added as fertilizer.Ammonium is a relatively immobileion, and it is not susceptible to leach-ing or denitrification as is nitrate

(NO3-). Corn takes up NH4

+ lessreadily than NO3

-. In most Kentuckysoils suitable for corn production,NH4

+ is rapidly converted to NO3- in

a process called nitrification. This re-action is largely completed shortly orwithin 30 days after fertilization.

Nitrate is a highly mobile ion be-cause its solubility in water is essen-tially unlimited. It is readily availableto plants but also is susceptible toleaching below the root zone, mainlyin well-drained soils subjected to long-lasting or very intense rainfall. Deni-trification loss of nitrate N is amicrobiological transformation thatcan proceed very rapidly when soilsbecome saturated with water. There-fore, it is most important in soils withimpaired drainage.

Some nitrate is lost almost everyyear in all Kentucky soils, but suchlosses become serious when heavy rainsor flooding occur within a month af-ter fertilizer application. These lossesresult in more N fertilizer being neededon poorly drained soils. The tillage sys-tem also influences these processes.Denitrification, leaching, and immo-bilization can all be greater in no-tillsoils, so N rates should generally beslightly increased when using the no-till system.

Figure 2. Corn leaf with nitrogen deficiencysymptoms (right) and a normal leaf.

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Organic SourceA winter legume cover crop can

also provide a substantial amount ofN for corn, either with no-tillage orconventional tillage. Research con-ducted by the University of Kentuckyindicates that some legume covercrops can provide yield advantagesbeyond N. Benefits from hairy vetchhave been greater than from crimsonclover or big flower vetch.

Nitrogen Fertilizers

Mixed FertilizersMost of the mixed fertilizers used

in Kentucky contain some N, with theamounts varying depending on thegrade. The first number in the guar-anteed analysis of a fertilizer refers tothe percentage of N. An 18-46-0grade is 18 percent N and contains18 pounds of N in each 100 pounds.Most of the N in mixed fertilizer is inthe ammonium form. Diammoniumphosphate and monammonium phos-phate are also commonly available N-containing fertilizers in which all theN is in the ammonium form.

Nitrogen MaterialsFertilizers that contain only N are

sometimes referred to as straight Nfertilizers. They are marketed in bothsolid and liquid forms. Nitrogen ma-terials commonly sold in Kentucky arediscussed below.

Ammonium Nitrate (NH4NO3) isa solid N fertilizer that contains 33.5to 34.5 percent N. One-half of the Nis in the ammonium form, and one-half is in the nitrate form. Ammoniumnitrate dissolves rapidly in the soil andis an excellent source of nitrogen, es-pecially for surface-applied N on no-till corn.

Urea (CO(NH2)2)) contains 45 to46 percent N in the solid form. Whenapplied to the soil, the enzyme ureasequickly converts urea N to ammo-nium. Consequently, urea N behav-ior in soil is essentially the same asthat of ammonium except for thevolatilization loss of NH3. The soil

near the urea granule becomes alka-line, which favors the formation ofNH3 gas from NH4

+. A large fractionof the N sometimes can be volatilizedas NH3 and lost to the air. Some ofthe factors that affect the amount ofloss are temperature, tillage, vegeta-tive cover, moisture, and soil pH.

If the urea is moved into the soilby a rain (0.25 inch is enough) or bytillage within two days after applica-tion, the volatilization loss is little ornone. When the urea is applied be-fore May 1, the loss is little to none,even without tillage or a rain withintwo days. However, after May 1 thevolatilization N loss is about 5 percentor less if urea is applied to the surfaceof a tilled soil, although it can behigher if the soil pH is near 7 or above.If the urea is applied to the surface ofa no-till field after May 1, the lossescan range from 0 to 25 percent, butthe average is about 10 percent. Thehigher losses come with a soil pH of 7or above or if the soil is warm andmoist but drying due to a good breeze.Surface application of urea to no-tillcorn after May 1 is risky.

Volatilization loss from urea can begreatly reduced or almost eliminatedby the use of urease inhibitors with thefertilizer. Urease inhibitors are very ef-fective, but their use is best justifiedeconomically with surface applicationof urea to no-till corn after May 1.

Nitrogen solutions contain N thatrange from 28 to 32 percent; 28 per-cent N solution is used in Kentuckybecause of its low salt-out potential. InN solutions most commonly used fordirect soil application, one-half of theN is from ammonium nitrate, and one-half is from urea. Each gallon of 28 per-cent, 30 percent, and 32 percent Nsolution contains 2.98, 3.25, and 3.54pounds of N, respectively. The volatil-ization losses of N from surface-appliedN solutions are much smaller thanfrom urea even though one-half of thefertilizer is in the urea form.

Anhydrous Ammonia (NH3) is thehighest analysis N fertilizer available,containing about 82 percent N. At or-dinary temperatures and pressure, it

is a gas and must be kept under pres-sure to be stored as a liquid.

When anhydrous ammonia is re-leased from pressure during applica-tion, the liquid immediately changesto a gas. For this reason, anhydrousammonia must be injected 6 or moreinches deep into the soil and thencovered immediately to prevent lossof ammonia gas to the atmosphere. Toprevent losses in no-tillage, extra seal-ing devices must be used. A wingedor beaver-tail-shaped piece of steel onthe injection knife is very helpful, butmany times an additional device, suchas a solid or spoked closing wheel oran inverted disc, is needed to close theknife opening. When injected intothe soil, the ammonia molecule(NH3) reacts with water and becomesammonium (NH4

+). The positivelycharged ammonium ion is then heldby soil particles until it is either con-verted to nitrate N by nitrificationover a period of several weeks or isabsorbed directly by plant roots or soilmicroorganisms.

The N in the injection band movesvery little laterally, so the roots mustgrow to the vicinity of the injectionband to come in contact with the N.Therefore, the plants may be N-defi-cient early in the growing season ifroot growth is slowed by cool and wetconditions or sidewall compaction. Ifsome N is broadcast before plantingor applied as in-row fertilizer, the po-tential for temporary N deficiency isoften relieved.

Anhydrous ammonia can also beapplied as a supercooled liquid. In thisprocess, anhydrous ammonia is re-leased and depressurized in a speciallybuilt converter that keeps 70 to 85percent of it as a liquid during appli-cation. In this state, the anhydrousammonia can be metered and cali-brated much more accurately.

Ammonium sulfate (NH4)2SO4contains about 21 percent N and 24percent sulfur. All the N is in the am-monium form, which is temporarilyabsorbed by the clay and organic mat-ter of the soil until it is nitrified tonitrate N or used by plants or micro-

23

organisms. Ammonium sulfate acidi-fies the soil much more quickly thanother sources of N. It is not subject tovolatilization loss.

Nitrate of Soda (NaNO3) contains16 percent N, all of which is in thenitrate form and readily soluble in thesoil solution.

Nitrogen Losses on Wet SoilsThe amount of N loss on wet soils

depends on the source of N used, thetime between N application and theonset of waterlogging, and the num-ber of days the soil is saturated. Ni-trogen can only be lost, due toexcessive water, when the N is in thenitrate form and is leached or lost bydenitrification. Denitrification is themore common cause of loss in Ken-tucky soils. The expected N loss fromperiods of heavy rains is found below.

Upland Soils Wet fromConstant Rains

These soils probably have not lostmuch N because it takes two to threedays of saturated conditions to beginthe denitrification process and thesesoils usually do not remain saturatedbetween rains. There may be some ex-ceptions here.

Lower Soils with ShortPeriods of Flooding (Oneto Two Days)

These soils stay saturated longer forseveral reasons, and the corn usuallylooks bad. The amount of N loss isstill not as great as one might assume.A N rate of 50 pounds per acre prob-ably would be the most a grower couldjustify adding to replace lost N inthese situations. Replicated trials bythe University of Kentucky in 1993showed increased corn yields of 11bushels per acre from sidedressing Nunder these conditions.

Flooded SoilsSince only nitrate is lost, we must

first estimate the amount of applied Nthat was in the nitrate form at the time

of flooding. Below are estimates of fer-tilizer in the nitrate form at 0, 3, and 6weeks after application. It is estimatedthat 3 to 4 percent of the NO3-N inthe soil will be lost by denitrificationfor each day the soil is saturated.

The NO3-N in a flooded sandy soilis leached more rapidly than othersoils, and the nitrate level would beexpected to be very low after the wa-ter recedes.

N source

Week afterapplication

0 3 6

% Fertilizeras NO3

-N

Anhydrous Ammonia (AA) 0 20 65

AA with N-Serve* 0 10 50

Urea 0 50 75

Urea with N-Serve* 0 30 70

UAN 25 60 80

Ammonium Nitrate 50 80 90

* Nitrification inhibitor that slowstransformation of ammonium to nitrate.

Nitrogen Soil TestAn additional tool for determining

NO3-N in the soil after flooding is aNO3-N soil test. The sample should betaken down to 12 inches deep, and sev-eral samples should be taken in eachfield of both the low and higherground. If the NO3-N is 0 to 10 ppm, afull rate of N for the crop potentialshould be added as a supplemental ap-plication. At 25 ppm, no additional Nwould be needed. One would extrapo-late between these two figures, keep-ing in mind the amount of NH4 left inthe soil from the first application.

Nitrogen InhibitorsThere are two types of inhibitors.

They are unrelated and are helpful intwo totally different situations.

Nitrification Inhibitors: Nitrificationinhibitors protect from loss of N dueto excessively wet soils. They are mosteffective on N fertilizers that aremainly in the ammonium form, suchas anhydrous ammonia, urea, and Nsolutions. When N in the ammoniumform is added to soil, it is rapidly trans-formed to nitrate. Nitrification inhibi-

tors slow the transformation for about4 weeks. This keeps N as ammoniumlonger so that it is not likely to leachor be lost by denitrification due toexcessive wetness. Economic benefitsare more likely on poorly drained soilsthat usually remain wet during spring.The economics of the use of a nitrifi-cation inhibitor must be weighedagainst other methods, such as add-ing more N to offset the loss (about35 pounds per acre) or sidedressing atleast one-half of the nitrogen whenthe corn is 6 to 12 inches high.

Urease Inhibitors: Urease inhibitorsprotect against losses of N from urea-based N sources to the atmosphere(volatilization). The losses are great-est for surface applied urea on no-tillcorn. See the urea section for discus-sion of this.

Timing N Applications: Probably themost practical and effective methodof increasing N recovery by corn is todelay or split the N application. Thispractice works because young cornplants (up to 4 to 6 weeks) requirevery little N, and in Kentucky mostof that can be supplied by the soil.Also, soils are typically wettest andmost prone to N losses early in theseason. Delayed N is most beneficialwhere the potential for denitrificationand leaching losses are greatest, par-ticularly on poorly, somewhat poorly,and moderately well-drained soils. Asa general guideline for these soils, iftwo-thirds or more of the N is applied4 to 6 weeks after planting, the totalN can be reduced by 25 to 50 poundsper acre. Fall application of N for cornis never recommended in Kentucky,and use of nitrification inhibitors withfall-applied N does not eliminate thesizeable overwinter N loss likely inKentucky.

Placement of N Fertilizer: The ap-plication of N below the soil surfaceimproves efficiency of N use in no-till corn but has very little benefit withtilled corn. When the N fertilizer isplaced below the residue layer of no-till corn, the N is less likely to be im-mobilized in the residue layer ashappens when fertilizer N is broadcast

24

on the surface. Subsurface applicationreduces the amount of N required by10 to 15 percent when compared tosurface broadcasting under no-tillconditions. More is discussed laterunder row fertilizers.

Recommended Rates of Nitrogen:Amounts of fertilizer N recommendedin Kentucky are affected by croppinghistory, type of tillage, internal soildrainage, irrigation, and time of ap-plication. Recommended rates can befound in the University of Kentuckypublication Lime and Fertilizer Recom-mendations (AGR-1).

Phosphorus andPotassium

Both phosphorus (P) and potas-sium (K) are required in large quanti-ties for good corn growth and yield.A good yielding crop will take up to50 to 70 pounds of phosphate (P2O5)and 130 to 170 pounds of potash(K2O) per acre (see Nutrient Contentand Removal section). Of this totaluptake, about three-fourths of thephosphate and about one-third of thepotash is in the grain. The remainderis in leaves, stalk, roots, husks, andcob. So for a grain production systemwhere all crop residues are left on thefield, 40 to 50 pounds P2O5 and 40 to50 pounds K2O per acre are removedfrom the soil each year. In silage pro-duction, all P2O5 and K2O taken upby the plant, except for that in theroots and stubble, are removed fromthe soil.

It is particularly important thatadequate P2O5 and K2O be availablefor plant uptake during the first halfof the season. By the time kernels startfilling rapidly (70 to 75 days after seed-ling emergence and 10 to 15 days af-ter silking), the plant will have takenup about 70 percent of its P2O5 re-quirements and nearly 90 percent ofits K2O requirements.

Availability from Soil: Both P andK are considered immobile elementsin the soil since they react with thesoil in ways that minimize theirmovement with soil water. This is

particularly true for P since, once inthe soil, it forms compounds withcalcium, iron, aluminum, manga-nese, and zinc, which are less solublethan the P compounds in the fertil-izer. If soil pH is in the range of 6.0to 6.5, much of the fertilizer P willreact to form calcium phosphates,which are more soluble than theiron, aluminum, and manganesephosphates that form at lower pHlevels. Therefore, greater P avail-ability is one benefit of good limingpractices. Potassium is retained onclays and organic matter by cationexchange. Except for very sandysoils, soil cation exchange capacityis great enough to hold an adequatereservoir of readily available K+. Forthese reasons, leaching of P and Kfrom Kentucky soils is of little im-portance. By comparison, loss of Pand K by erosion of topsoil is ofmuch greater concern.

Corn grown on fields being rotatedfrom a tilled sod may respond less toP fertilization than expected from thesoil test results. This is because P willbe released as organic residues fromthe sod as it decomposes.

Requirements: The amount of P andK fertilizer required for good corngrowth is directly related to theamount of plant-available P and Kalready in the soil. Using a reliable soiltesting laboratory that makes fertilizerrecommendations based on field-tested procedures is the best way todetermine levels of plant-availablesoil P and K. The annual amount of Pand K taken up by the plant from fer-tilizer is not likely to exceed 15 to 20percent of the P or 25 to 40 percentof the K applied.

Sources: Commercial fertilizer isthe most widely used source of P andK for corn production. The sources ofP most commonly used are triple su-perphosphate (0-46-0), diammoniumphosphate (18-46-0), monoammon-ium phosphate (11-48-0), and a widearray of other ammoniated phos-phates, both liquid and dry. Most com-monly used sources of fertilizer P areconsidered equally effective for agro-

nomic purposes when used at recom-mended rates and properly applied.Solid and liquid forms of P are alsoconsidered equally effective.

Almost all K fertilizer used for cornis muriate of potash (0-0-60). Otheravailable sources are sulfate of potash(0-0-50) and sulfate of potash mag-nesia (0-0-18, 11 S, 18 Mg). All areconsidered equally effective.

Organic sources of P and K such asanimal manures and sewage sludgemay also be used. Since their nutri-ent content varies, analysis is neces-sary to determine appropriate rates. Itis important to know the content ofheavy metals (nickel, cadmium, andchromium) in municipal and indus-trial sludges in order to prevent toxicbuild-up.

Placement: Broadcasting P and K isthe most convenient method of ap-plication, although at low to very lowsoil test levels, large amounts are re-quired. Banded applications (2 inchesto the side and 2 inches below theseed) can increase agronomic effi-ciency of P and K, making it possibleto decrease the usual rate by one-thirdto one-half. A “starter” effect (im-proved initial growth) is likely to re-sult from band placement. This mayappear very significant during theearly growing season, but in Kentuckyit rarely increases yield, provided thatbroadcast P and K fertilizers are usedat recommended rates.

Rates: Rates of phosphate and pot-ash recommended by the Universityof Kentucky can be found in theAGR-1 publication.

Secondary Nutrients andMicronutrients

MagnesiumMagnesium levels in soils range

from high (chiefly the loess-derivedsoils) to low (primarily some sand-stone-derived soils). Soil test levelsand recommended Mg rates can befound in AGR-1. Deficiency of Mg israre in Kentucky and is most likely tobe found on sandy soils.

25

Calcium and SulfurCalcium deficiency of corn has

never been documented in Kentucky.Despite concerns about reduced atmo-spheric sulfur fallout, no verified sul-fur deficiency on corn has beenrecorded. University of Kentucky testsof sulfur application to corn during the1990s and before did not show a yieldresponse to its use. If deficiency oc-curs, it is most likely to be found onsandy soils.

ZincZinc deficiencies in corn are com-

mon in Kentucky in limestone soils,particularly when soil pH is above 6.5.The deficiency symptom most com-monly noticed are broad whitishstreaks down the leaves of young cornseedlings (see Figure 3). If corn plantsare carefully removed from the soiland the stalk is carefully split all theway to the bottom tip of the plant,the presence of a purplish discolora-tion at the lower nodes is another dis-tinctive indicator of zinc deficiency.If the deficiency is severe, seedlingsmay die. In mild cases, internodegrowth is limited, stunting plantheight. Leaves may also show purplishedges, and ears may cup to one sideand not fill completely. Where zincdeficiency of corn is suspected or hasoccurred previously, a zinc soil test ishelpful in determining if zinc shouldbe applied. A table found in AGR-1lists soil test zinc levels at various soilpH ranges and soil test P levels belowwhich a response to zinc fertilizationis likely to occur. However, manyother factors, including weather con-ditions, affect availability of soil zincto corn, making it difficult to predicta response to added zinc for a specificgrowing season. Zinc fertilizer recom-mendations can be found in AGR-1.

BoronBoron deficiencies in corn have

been documented in Kentucky, butthey are not common. Plant tissueanalysis is the best way to test for thisdeficiency. If the ear leaf sample con-tains less than 5 parts per million

(ppm) and the soil test value is lessthan one ppm, an application of 2pounds of boron per acre might bebeneficial.

Other NutrientsDeficiencies of other nutrients such

as manganese, iron, copper, molybde-num, chlorine, and cobalt are ex-tremely unlikely for corn in Kentucky.If a problem is suspected, tissue analy-sis is recommended.

Row FertilizersThe use of row fertilizer and its po-

tential benefits vary with conditions.The efficiency of fertilizer is greatlyincreased by banding fertilizer and ishelpful on soils with a low soil test. Insuch cases, the rate of P and K can bereduced by one-third to one-half. Forsoils testing medium or high, a suffi-cient amount of P and K nutrientsexists in the soil such that additionalfertilizer applied near the row is notlikely to increase yields. Regardless ofsoil test, banded fertilizer will usuallyincrease the vigor and early growthof corn.

Yield increases may sometimes beachieved with starter fertilizer contain-ing N and P, when placed beside or inthe row, but they are not always eco-

nomical. The consistency and amountof the yield increase response dependson soil type, tillage, planting date, andweather. Conditions that place thecorn under prolonged stress early in thegrowing season increase the chancesof a positive response and the amountof the response. The response is moreconsistent and larger for early plant-ing of no-till corn on soils that are notwell drained. Although not as consis-tent, responses to starter fertilizers arealso found on early planted no-till cornon well-drained soils. Responses will bemuch smaller in warmer years and withlater plantings. The average yield in-crease expected from row fertilizer isshown in Table 2.

Expected Yield Responseto Row Fertilizer

Most of the response to starter fer-tilizer in Kentucky soils is response toN. The rest of the response can beachieved by adding P. Potassium hasvery little effect on the early growth.If the fertilizer is placed in the seed fur-row, only 10 to 15 pounds per acre eachof N and P2O5 are needed. Increasingthe rate higher than this will not im-prove the starter effect and may ad-versely affect seed germination. If thefertilizer is banded beside the row (2"x 2"), research indicates that 20 poundsper acre each of N and P2O5 are neededto achieve an optimal effect.

To prevent germination and emer-gence problems, the amount of N plusK2O should be limited to no more than15 pounds per acre (as shown from re-cent research) in the furrow and nomore than 100 pounds per acre in a 2"x 2" placement beside the row. An Nsource that contains only urea adds ad-ditional risk due to high levels of am-monia generated in the placement area.

Plant AnalysisPlant analysis is the laboratory de-

termination of nutrient elements ona sample of plant tissue. In recentyears, this technique has been morefrequently used to diagnose nutri-

Figure 3. Corn leaf with zinc deficiency (left)and a normal leaf.

26

tional problems relatedto soil fertility or tomonitor effectivenessof fertilizer practiceson growing crops.

A plant analysisprogram is not a sub-stitute for soil testingbut is most effectivewhen used in conjunc-tion with a regular soiltesting program.

The most common elements ana-lyzed for plant analysis are nitrogen (N),phosphorus (P), potassium (K), calcium(Ca), magnesium (Mg), iron (Fe), man-ganese (Mn), boron (B), copper (Cu),zinc (Zn), and aluminum (Al). Othersthat may be measured either routinelyor upon request include sulfur (S), so-dium (Na), molybdenum (Mo), cobalt(Co), silicon (Si), cadmium (Cd),nickel (Ni), lead (Pb), chromium (Cr),arsenic (As), and selenium (Se). Al-though some of these are not essentialfor plant growth, the results may be usedfor interpretation and recommenda-tions, or for identifying toxic levels ofsome elements. Considerable care mustbe given to collecting, preparing, andsending plant tissue to the laboratoryfor analysis.

Table 4. Nutrient content of and removal by corn plant parts.

Plant part

Content (% by dry weight)

N P1 K2 Ca Mg

Grain 1.30 0.28 0.50 0.12 0.16

Stover 0.70 0.15 1.20 0.37 0.16

Plant part Unit

Removal (lb/unit)

N P2O5 K2O

Corn Grain Bu. 0.7 0.4 0.35

Corn Silage Ton 7.5 3.6 8.0

Corn Stover Ton 15 7 301 P x 2.29 = P2O52 K x 1.2 = K2O

Table 3. Nutrient sufficiency levels for corn.1

Nutrient

Type of sample

Whole plantsless than 12inches tall

Leaf below whorl,plants more than

12 inches tall

Ear leaf attasseling beforesilks turn brown

N 3.5-5.0% 3.00-3.50% 2.75-3.00%

P 0.3-0.5% 0.25-0.45% 0.25-0.45%

K 2.5-4.0% 2.00-2.50% 1.75-2.25%

Ca 0.3-0.7% 0.25-0.50% 0.25-0.50%

Mg 0.15-0.45% 0.13-0.30% 0.13-0.30%

S 0.15-0.50% 0.15-0.50% 0.15-0.50%

Mn 20-300 ppm 15-300 ppm 15-300 ppm

Fe 50-250 ppm 30-200 ppm 30-200 ppm

B 5-25 ppm 4-25 ppm 4-25 ppm

Cu 5-20 ppm 3-15 ppm 3-15 ppm

Zn 20-60 ppm 15-60 ppm 15-60 ppm

Mo 0.10-10.0 ppm 0.1-3.0 ppm 0.1-3.0 ppm1 From Plant Analysis Handbook for Georgia. Bulletin 735. Univ. ofGeorgia Cooperative Extension Service, 1979.

Table 2. Expected yield response to row fertilizer.

Tillage Soil drainageConsistency of

response

Averageyield*

increase(bu/ac)

Tilled All types Occasional 0-1

No-tilled Well-drained Sometimes 1-6

No-tilled Not well-drained Most of the time 5-7

* The average yield response includes all yield responses, bothpositive and negative. There will be times when the yieldincrease is greater due to cooler and wetter years than normal,and in some unusual situations there can even be a negativeresponse.

SamplingRandomly sample plants through-

out a uniform field or sampling area.When a nutrient deficiency is sus-pected or abnormal growth is present,collect one sample from the affectedarea and a sample from an adjacentnormal area. Collect the plant tissuein a new, clean brown paper bag. Dustyor soil-covered leaves and plantsshould be avoided. If leaves have aslight dust cover, brush gently with asoft brush or perform a “quick rinse”with distilled water. Do not prolong thequick rinse or use a soap solution asnutrient elements will be leached outof the tissue. Do not include damaged,diseased, or dead tissue in your sample.

Good results require sampling a defi-nite plant part. For corn less than 12inches tall, cut 20 plants at 1 inchabove the soil surface. For corn taller

than 12 inches but which has not tas-seled, pull the entire first mature leaf(completely unrolled) below the whorlfrom 20 plants. Fully developed plantsshould be sampled when 50 percent ofthe ears show silks. Sample the wholeear leaf (the leaf just below the ear)from 20 plants. Do not take samplesafter the silks have turned brown.

For diagnostic purposes, a good rep-resentative soil sample should also becollected. When problem areas existin the field, take one sample from theaffected area and one sample from anadjacent normal area. Take cores orsubsamples adjacent to plants that areselected for tissue sampling.

Sufficiency Level ofNutrients

Table 3 summarizes nutrient levelsthat would be considered sufficient.Levels below those shown might beinsufficient for optimal yields.

Nutrient Content andRemoval by Corn

Estimated nutrient content ofhealthy, mature corn and the amountsof nutrients taken up are shown inTable 4. Data were provided by theUniversity of Kentucky.

27

Weed ManagementJ. D. Green and James R. Martin

The most economically importantpests that reduce corn yield each yearare unwanted plants that interferewith corn growth, development, orharvest. These plants, called weeds,compete with corn for water, light,and soil nutrients to reduce crop yield.Some weeds are capable of naturallyreleasing substances into the soil thatare allelopathic, or toxic, to the crop.Weeds can serve as hosts for corn dis-eases, such as the maize dwarf mosaicand maize chlorotic dwarf virus com-plex (MDM/MCD) on johnsongrassrhizomes, which can be vectored andtransported by insects to corn plants,thus reducing crop yield. Weeds alsoprovide shelter and serve as a foodsource for insects and diseases thatoverwinter or provide habitat for wild-life species such as prairie voles thatreduce corn stands.

A number of decisions must beconsidered in developing a successfulweed control program. To assist inweed management decisions, a cornproducer must be able to properlyidentify the specific weed problems ineach field along with other aspectsand factors that might influence weedemergence and growth. It is also im-portant to understand the life cycleof weedy plants, their growth habit,and their potential competitiveness orimpact on the crop.

Life Cycles of WeedsWeeds can be grouped into three

major categories. Annuals completetheir life cycle in one growing seasonand reproduce only by seed. Summeror warm-season annuals, such as largecrabgrass (Digitaria sanguinalis) andcommon cocklebur (Xanthiumstrumarium), germinate in the springand set seed in late summer or fall.These plants are more likely to directlycompete with the corn. Winter or cool-season annuals typically germinate inthe fall and complete their reproduc-

tive cycle in the spring or early sum-mer. Therefore, cool-season annualplants, such as common chickweed(Stellaria media) and Italian ryegrass(Lolium multiflorum) are generally moreof a concern at the time of plantingand during the early stages of corngrowth in no-till corn production.

Biennials are capable of complet-ing their life cycle during two grow-ing seasons. The first year normallyconsists of vegetative growth, whereasthe second year involves both vegeta-tive and flower development. Bienni-als, such as musk thistle (Carduusnutans), reproduce only by seed.Sometimes these plants may completetheir life cycle within one year.

Perennial plants are capable of ex-isting for more than two years. Repro-duction can be by seed and byvegetative structures such as rhizomes,

Table 1. Common and troublesome weeds and their life cycle in Kentucky corn fields.

Weed species Life cyclePrimary

reproductionNative/

Introduced

10 Most Commonly Occurring Weeds

smooth pigweed SA seed N

giant foxtail SA seed I

large crabgrass SA seed I

johnsongrass P seed, rhizome I

morningglory (ivyleaf & pitted) SA seed I

honeyvine milkweed P seed, creeping root N

fall panicum SA seed N

common cocklebur SA seed N

giant ragweed (horseweed) SA seed I

yellow nutsedge P tuber, rhizome, seed N

10 Most Troublesome Weeds to Control

honeyvine milkweed P seed, creeping root N

broadleaf signalgrass SA seed N

burcucumber SA seed N

trumpetcreeper P creeping root, seed N

giant ragweed (horseweed) SA seed I

johnsongrass P seed, rhizome I

common pokeweed P seed, taproot N

ivyleaf morningglory SA seed I

fall panicum SA seed N

Italian ryegrass WA seed I

Life cycle: SA = summer or warm-season annual; WA = winter or cool-season annual; P = warm-season perennial. Origin: I = introduced plant; N = native plant.

stolons, tubers, taproots, or creepingroots. For example, johnsongrass (Sor-ghum halepense) plants frequently en-countered in corn fields emerge fromseed; however, johnsongrass plants arecapable of emerging from rhizomes.Warm-season perennial weeds havebecome of increasing concern as no-tillage practices have increased inKentucky’s crop production systems.Ten of the most common and trouble-some weeds found in Kentucky cornfields are listed in Table 1.

Weed ScoutingProper weed identification is an

essential component of any success-ful weed management program. It iseven more critical in no-tillage sys-tems because herbicides are the pri-mary method of weed control.

28

Training and a skilled eye are oftenneeded to properly identify weeds dur-ing early vegetative growth stages. Infact, an effective postemergence con-trol strategy for weeds often dependson proper identification when weedsare less than 4 inches tall. Thus, fieldscouting should begin within 2 weeksof corn planting and continue atweekly intervals for 8 to 10 weeks intothe growing season. Scouting meth-ods recommended for weeds in corncan be found in Kentucky IntegratedCrop Management Manual for FieldCrops—Corn (IPM-2) available atyour county Extension office.

A history of previously knownweed problems in a field greatly aidsin preparing an overall weed controlstrategy at the beginning of the grow-ing season. Knowing the previous fieldhistory can also provide insight ontheir identity when weeds emerge. Agood method for developing a fieldhistory of weed problems is by map-ping weeds from previous and currentfield scouting reports and from obser-vations made at harvest. A detailedweed map for each field will provideinformation on the location of weedinfestations and help monitor changesin these infestations from year to year.

Weed and CornInteractions

An economic threshold existswhen a weed population reaches alevel whereby it becomes economi-cally justified to control because of thepotential for corn yield reduction,crop quality loss, harvesting difficul-ties, or other problems caused by theweeds. Low weed populations do notinterfere with crop yield, har-vestability, or crop quality. Thus, pro-ducers may allow low populations ofweeds to remain in the field through-out the growing season without affect-ing the crop. On the other hand, vinyweeds such as burcucumber (Sicyosangulatus) can reduce yield and inter-fere with corn harvest at low plantpopulations. Other weed species such

as smooth pigweed (Amaranthushybridus) and common lambsquarters(Chenopodium album) are capable ofproducing thousands of seeds from asingle plant. Therefore, it can be agood strategy to control low popula-tions of such annual weeds. The over-all impact that replenishing the soilseed bank may have, when someweeds are allowed to grow throughmaturity, is not fully understood. It isalso desirable to control light infesta-tions of perennial weeds and newly in-troduced annuals before they becomea serious problem. The anticipatedyield loss from various weed popula-tions is illustrated in Table 2.

Most weed-corn competition stud-ies indicate weeds that emerge andgrow with corn during the first 2 to 4weeks under normal environmentalconditions, and then removed, do notreduce corn yield. In addition, if weedsare kept out of the field for up to 4 to 6weeks after corn emergence, weeds thatemerge later are not likely to reduceyield relative to the cost of treatment.However, late emerging weeds maycause harvest problems or reduce cropquality depending on the weed species.

Table 2. Estimated impact on corn yield with different weed species at various populations incorn with a 100 bu/ac yield potential.1

Weed pressurecategory(yield loss potential) F

oxt

ail s

pp

.

Jo

hn

son

gra

ss

Pig

wee

d s

pp

.

Mo

rnin

gg

lory

sp

p.

Co

mm

on

Co

ckle

bu

r

Gia

nt

Rag

wee

d (H

ors

ewee

d)

Estimatedyield loss by

a singlespecies

Estimatedyield loss by

all species

-- Weed density per 100 sq ft -- (bu/ac) (bu/ac)

Slight (0-5%) 10 8 5 5 4 2 <2 <10

Low (5-10%) 20 15 10 10 8 4 5 20

Moderate (10-20%) 50 30 25 30 10 8 10 30

Severe (20-35%) 100 75 50 60 30 20 20 40

Very Severe (>35%) 200 125 75 100 50 40 35 501 These specific plant density values are based on general observations, and estimates showrelative differences among individual weed species. Estimated values can vary greatlydepending on the environment and when the weeds emerge relative to the time of cropemergence. Adapted from University of Missouri-Columbia Extension bulletin “IntegratedPest Management—Practical Weed Science for the Field Scout Corn and Soybeans,” February2001.

Impact of TillageManagement practices used in

Kentucky and surrounding states em-phasize reducing tillage in a rotationof corn, wheat, and double-croppedsoybeans during a two-year period.This tillage and rotation system offersboth benefits and drawbacks with re-gard to weed management.

No-tillage practices provide nu-merous benefits for weed control, andoften a shift in the dominant weedswill be noticed. Undisturbed soil, withtime, reduces the germination of weedseed that are deep in the soil seedbank. The fact that no-tillage limitsthe amount of soil disturbance andscarification of weed seeds may ex-plain why such weeds as commoncocklebur, burcucumber, andsicklepod (Cassia obtusifolia) are ob-served to a lesser extent in no-tillagecompared to more intensive tillagesituations. Furthermore, leaving thesoil undisturbed for several years maylead to rotting and/or predation ofseeds on the soil surface.

The lack of soil disturbance maypromote the development of popula-tions of certain weed species. The in-

29

cidence and severity of weeds such ascommon pokeweed (Phytolaccaamericana) and curly dock (Rumexcrispus) are examples of perennials withlarge fleshy tap-roots that grow well ina no-tillage environment. Also, an oc-currence of some annual weed speciessuch as marestail (i.e., horseweed)(Conyza canadensis) and prickly lettuce(Lactuca serriola) are noticed more fre-quently under no-tillage conditions.These two weed species can emergeduring the late fall or early wintermonths and maintain active growththroughout the corn growing season.Perhaps one reason marestail andprickly lettuce become established isthat their seedlike achenes with tuftsof hair are spread easily by wind. Thus,they can easily invade fields where pri-mary tillage is not used to destroy emer-gence of new plants.

Poor control of perennial weeds isa major complaint about no-tillagecorn production. Common pokeweedwith its perennial tap-root systemgrows well and is difficult to controlin a no-tillage system. Honeyvinemilkweed (Ampelamus albidus) andtrumpetcreeper (Campsis radicans) arewarm-season perennial vines withcreeping roots, whereas Italianryegrass is a cool-season annual grassthat often escapes control from tradi-tional burndown herbicides but is eas-ily controlled with spring tillage.

Since less tillage leaves previouscrop residue on the soil surface, thatresidue intercepts some of the herbi-cide spray when it is applied. Less resi-due is present if the previous crop wassoybean compared with corn stubbleor when the previous crop was wheat.A rainfall event occurring soon afterapplication generally moves the her-bicide off the crop residue and in con-tact with the soil. This reflects theimportance of rainfall, instead of me-chanical incorporation, as the avenueby which a major portion of the her-bicide is moved within close proxim-ity to germinating weed seeds. Someherbicides intercepted by crop residuemay be subjected to loss by processessuch as photodecomposition or by

volatilization. In general, researchdata have not indicated that perfor-mance of soil-active herbicides isgreatly reduced as a result of crop resi-due left on the soil surface. However,the thick surface mulch often associ-ated with long-term no-tillage pro-duction may be one factor thatcontributes to inconsistent control ofbroadleaf signalgrass (Brachiariaplatypylla) with the chloroacetamideherbicides. The mulch may also slowthe warming of soil and delay emer-gence of such weeds as johnsongrass.Delaying the emergence ofjohnsongrass may limit the opportu-nities to apply postemergence herbi-cides for optimum control withminimum risk to corn.

One noted effect of more residueon the surface is the change in soilcharacteristics at the soil surface.Generally, under continuous no-tillcorn production an increase in soil or-ganic matter occurs from decayingcrop residue, and often the soil sur-face pH becomes more acidic becauseof annual additions of nitrogen fertil-izers. These two factors can changethe effectiveness and the persistenceof some herbicides. For example, thetriazine herbicides, such as atrazineand simazine (Princep, etc.), tend topersist less and may provide less weedcontrol in a no-tillage system com-pared to conventional tillage. Thiscan be explained by a faster degrada-tion rate of triazine herbicides underacidic conditions (pH 5.0). Timely ap-plications of lime will overcome thispH effect. On the other hand,overapplication of lime may result inhigh soil pH levels (pH 7.0) that cancause herbicide carryover concerns toother rotational crops.

Cultural Practices andMechanical Controls

In addition to a scouting programand field mapping of weed problems,a good program of integrated weedmanagement should employ a varietyof crop management tools to deal withweed problems. These include pre-

venting the introduction of newweeds and cultural practices such asseeding rates and planting dates thatmaximize the competitiveness of thecrop. This allows the corn to competebetter with weeds by reducing weedseed emergence and growth. Me-chanical methods, such as minimumtillage cultivators capable of function-ing in high crop residue, will provideweed control between the rows.

Crop rotation can also be an effec-tive tool for managing some problemweeds. It helps limit the increase inthe population of some perennial ordifficult-to-control weeds in continu-ous crop production systems. For ex-ample, johnsongrass can be difficultto control in corn but easier to con-trol in soybean because a wider vari-ety of herbicide options are available.Rotation to densely planted crops(i.e., forages or small grains) cansmother some weeds, such as crab-grass, that compete in row crops. Ro-tation of crops also allows for moreopportunities to rotate herbicides,which in turn helps prevent the de-velopment of herbicide resistance insome weed species.

Herbicide Useand Timing

Herbicides are the primary methodof weed control in corn production.They are particularly important forcombating weed problems in no-tillor conservation tillage production sys-tems. Herbicides are generally consid-ered to be either soil active or foliaractive. Soil-active herbicides are gen-erally applied to the soil surface sincethey are most effective shortly afterweed seed germination, whereas fo-liar-active herbicides control weedsafter they have emerged from the soil;thus, they are applied postemergence(POST) to the weeds.

Soil-active herbicides are usuallyapplied to the soil surface (i.e.,preemergence [PRE]) before the cropand weeds emerge. Herbicide productsthat contain atrazine, pendimethalin(e.g., Prowl), or other soil-active in-

30

gredients can also be applied aftercorn emergence but before weedsemerge. Some soil-active herbicidescan also be incorporated into the soilbefore crop planting and weed emer-gence (i.e., preplant incorporated[PPI]). Preplant-incorporated herbi-cide applications are possible withcrop management systems that leavesome surface residue but not in no-till corn production. This narrows thelist of potential herbicides availablefor use. Herbicides applied to the soilsurface are more dependent on rain-fall to move the herbicide into theweed seed zone compared to herbi-cides mechanically incorporated.Weeds, such as broadleaf signalgrass,Eastern black nightshade (Solanumptychanthum), and yellow nutsedge(Cyperus esculentus) that are more sus-ceptible to herbicides applied preplantincorporated, are less effectively con-trolled with herbicides applied to thesoil surface.

In no-tillage systems herbicides areusually needed for vegetation controlprior to crop emergence (i.e., preplantfoliar [PPF]). Paraquat (Gramoxone),glyphosate (Roundup, Touchdown,etc.), dicamba (Banvel, Clarity, etc.),and 2,4-D are often used to“burndown” the existing vegetation(Table 3). In many cases, the greenvegetation present among the previ-ous crop residue consists of cool-sea-son annuals and perennials, alongwith some emerging summer annualweeds. When planting corn into a pe-rennial grass or grass/legume sod,treatment combinations of atrazineplus paraquat or glyphosate providethe best control. Glyphosate appliedin the fall is generally more effectivefor killing sod crops, especially infields containing orchardgrass, fescue,alfalfa, and/or other forage legumes.To control alfalfa in the spring priorto planting corn, dicamba (Banvel,Clarity, etc.) should be used.

Where previous crop residue exists,an alternative to “burndown” appli-cations at planting is to apply herbi-cides several days prior to planting(i.e., early preplant [EPP]). In corn,

soil-active herbicides can be appliedas a sequential treatment with the firstapplication made 15 to 30 days be-fore planting and the second at plant-ing. Single applications can besuccessful as much as 15 days aheadof planting. When an early preplantherbicide program is used in corn, anonselective “burndown” herbicidemay not be needed.

Herbicide formulations are chang-ing to fit the needs of crop produc-tion. Package mixtures of herbicideswith more than one active ingredienthave become prevalent due to theneed for a broad spectrum of weedcontrol activity. Water dispersiblegranules and dry flowable herbicideformulations with low use rates havealso increased. Some specialized her-bicide formulations can reduce the“binding” of the herbicide with theplant residue left on the soil surface(i.e., micro-encapsulated). Other for-mulation changes that may evolve inthe future include the developmentof formulations that reduce volatiliza-tion loss of surface-applied herbicides.

In recent years there has beengreater reliance on postemergenceherbicides. Certain weeds, especiallywarm-season perennials, may not bereadily controlled by preemergence

Table 3. Relative response of cover crops and weeds to burndown herbicides.

Herbicide1

Cover crops Weeds

Alf

alfa

Clo

ver,

Red

Clo

ver,

Wh

ite

Fes

cue,

Tal

l O

rch

ard

gra

ss R

ye R

yeg

rass

, An

nu

al V

etch

, Hai

ry W

hea

t B

rom

e sp

p.

Ch

ickw

eed

, Co

mm

on

Dan

del

ion

Do

ck, C

url

y F

leab

ane,

An

nu

al F

oxt

ails

Hen

bit

/ D

ead

net

tle

Let

tuce

, Pri

ckly

Mar

esta

il M

ust

ard

sp

p.

Th

istl

e, M

usk

Jo

hn

son

gra

ss (s

eed

ling

) J

oh

nso

ng

rass

(rh

izo

me)

Po

kew

eed

Rag

wee

d, G

ian

t

Atrazine 3 5 4 6 3 6 5 6 6 7 9 4 4 - 6 8 9 9 8 4 0 0 2 9

Dicamba 8 9 8 0 0 0 0 8 0 0 7 8 7 8 0 6 9 7 7 8 0 0 6 9

2,4-D Ester 6 8 5 0 0 0 0 8 0 0 5 8 4 6 0 4 8 8 8 7 0 0 5 8

Paraquat 3 7 5 5 3 7 6 7 7 7 9 4 2 6 9 8 5 4 6 3 7 3 4 7

Paraquat + Atrazine

4 - - 8 7 7 7 8 9 8 9 7 5 - 9 9 9 9 9 5 7 3 4 9

Glyphosate 6 6 5 7 6 8 7 6 9 9 9 6 4 8 9 8 8 9 8 6 9 8 6 9

Good = 8-9 Fair = 6-7 Poor = 5 or less _ Insufficient Data1 Herbicide products that contain these active ingredients include atrazine (AAtrex, etc.);dicamba (Banvel, Clarity, etc.); paraquat (Gramoxone); and glyphosate (Roundup, Touchdown,Glyphomax, etc.).

treatments. In addition, weed escapes(due to resistance or environmentalconditions not conducive to weedcontrol) must be treated withpostemergence herbicides. Post-emergence herbicides also provide thebenefit of allowing the use of a moreintegrated weed management ap-proach since herbicides are appliedonly when needed.

Herbicide Persistence andCarryover

Paraquat and glyphosate are tightlybound to soil and offer no soil-residualactivity, whereas atrazine (AAtrex orAtrazine) and simazine (Princep) canremain active in soil for a period oftime. While persistence of herbicidesin soil is beneficial in regard to weedcontrol, it is a concern when associ-ated with carryover to rotational cropsor other environmental impacts.

The risk of injury from herbicidecarryover is dependent on several fac-tors including the susceptibility of ro-tational crops and the persistence ofthe herbicide. The typical cropping se-quence used in Kentucky and portionsof neighboring states include corn,wheat, and double-cropped soybean. Inthis cropping sequence crop injury

31

from carryover seldom occurs fromherbicides used in Kentucky. However,some soybean herbicides such asimazaquin (e.g., Backdraft, Scepter,Squadron, Steel), imazethapyr (e.g.,Extreme, Pursuit), and chlorimuron(e.g., Canopy, Canopy XL, Classic,Synchrony) have potential to persistlong enough to injure corn. Corn her-bicides such as atrazine and simazinehave label precautions for rotating towheat or soybean.

Certain herbicide-tolerant cropscan limit the risk of injury from her-bicide carryover. ClearfieldTM cornhybrids have a high degree of toler-ance to imidazolinone herbicides;consequently, they have more flexibil-ity than regular hybrids when rotat-ing to corn where imazaquin wasapplied the previous season under drysoil conditions. Similarly, STS soy-beans are tolerant to many sulfony-lurea herbicides and are recom-mended where prosulfuron-contain-ing products (e.g., Exceed, Spirit)were applied to corn during condi-tions that limited herbicide degrada-tion processes.

Environmental conditions also af-fect herbicide persistence and rota-tional crop injury. Factors that helppromote herbicide dissipation andlimit carryover problems in Kentuckyinclude: 1) an ample supply of mois-ture throughout the growing season,2) mild winter temperatures, 3) rela-tively low levels of organic matter(usually 2 to 3 percent), and 4) soilswith medium pH levels (usually pH6.0 to 6.8).

Many of the soil-active herbicidesused in corn have the potential to con-taminate surface and groundwater. Thelabels of these products have ground-water advisory statements that recom-mend not applying where the watertable is close to the surface and wherethe soils are very permeable. Atrazine-containing products have special labelrestrictions for use near ground or sur-face waters. Emphasis is placed on us-ing low atrazine rates, buffer zones, andconservation tillage practices as strat-

egies for minimizing the risk of con-taminating water sources.

Herbicide InteractionsMixing herbicides with other

chemicals, either as tank mixtures orsequential applications, is practicedwidely. It is important to recognize thepotential benefits as well as drawbacksfor using such strategies. The “jar test”method that is described on manyproduct labels helps determine physi-cal signs of compatibility of tank mix-tures but will not indicate thepotential for synergism (i.e., enhance-ment) or antagonism (i.e., less activ-ity) as it relates to crop injury or weedcontrol.

Nitrogen fertilizers such as 28 to 32percent liquid nitrogen, 10-34-0, orammonium sulfate are sometimes usedas additives with postemergence her-bicides. Although the benefit of thesematerials as additives is debatable forcertain herbicides, there are situationswhere their use can enhance controlor limit antagonism. It is well knownthat the use of nitrogen fertilizers asan additive enhances postemergencecontrol of velvetleaf. Ammonium sul-fate and liquid nitrogen may reduceactivity of Accent Gold, whereas 10-34-0 is the preferred source of nitro-gen as an additive with this product.The sequence in which nitrogen fer-tilizers are added in the spray mixturesmay also impact the activity of cer-tain herbicides. For example, it is rec-ommended that ammonium sulfate beadded first in the spray mixture tolimit antagonism of certain tank mix-tures with Roundup Ultra and otherglyphosate products in hard water orwith certain herbicides.

While herbicide interactions withinsecticides are seldom a problem,there are situations where their use astank mixtures or sequential sprays canresult in problems. Corn injury canoccur when tank mixing certainAcetolactate Synthase (ALS)-inhib-iting herbicides with organophos-phate insecticides. The use ofinsecticides and herbicides as separate

applications in the same field, such asin-furrow treatments of certain orga-nophosphate insecticides followed bypostemergence sprays of ALS-inhib-iting herbicides, may result in corninjury.

The risk of antagonism varies de-pending on specific products, methodsof application, and environmentalconditions. Some products are notstable in water over time and shouldbe sprayed soon after mixing. This isespecially true of many of the sulfony-lurea herbicides, which may degradewithin four to 24 hours after mixing.Consulting the labels of all materialsinvolved in a spray mixture will helpavoid physical incompatibility issueswith mixing, as well as potential prob-lems with crop injury, or weed control.

Herbicide-ResistantWeeds

A major concern in weed manage-ment is the resistance of weeds tocommonly used herbicides. Not allpigweed plants are created alike. Norare all common lambsquarters orjohnsongrass plants the same. Thereis genetic diversity among plants ofthe same species. Sometimes this di-versity is expressed by small differ-ences in the physical appearance ofthe plants. These differences can alsobe expressed as a differential responseto herbicides. The basis for herbicideresistance is the fact that genetic di-versity allows biotypes within a spe-cies to survive a herbicide treatmentthat is generally known to be lethalto that plant species.

Examples of herbicide-resistantweeds documented in Kentucky cornfields include smooth pigweed to tri-azine type herbicides (i.e., Atrazineand Princep) and to ALS-type herbi-cides (i.e., Accent, Beacon, Exceed,etc). The potential for weed resistanceto develop increases with a continu-ous use of a herbicide or herbicideproducts that have the same mode ofaction on the same field for severalseasons. Therefore, herbicide useshould be monitored and production

32

practices implemented to prevent andreduce the potential for weed resis-tance to occur.

A key to avoiding developmentof herbicide-resistant weed popula-tions is prevention. Listed below aremanagement strategies to considerin preventing and dealing withherbicide-resistant weeds.• Scout fields regularly and identify

weeds present. Respond quickly toshifts in weed populations to re-strict spread of weeds.

• Select a herbicide based on weedspresent and use a herbicide onlywhen necessary.

• Rotate herbicides. Avoid using thesame herbicide or another herbi-cide with the same mode of action(i.e., herbicides that inhibit thesame process in target weeds) fortwo consecutive years in a field. Itis possible for a herbicide used inone crop to have the same mode ofaction as a different herbicide usedin another crop. For example, Ac-cent, Basis, Beacon, Canopy, Clas-sic, Exceed, FirstRate, HarmonyExtra, Harmony GT, Lightning,Permit, Pursuit, Python, Scepter,Spirit, and Synchrony “STS” con-tain active ingredients with thesame mode of activity in plants(i.e., these herbicides are ALS in-hibitors).

• Apply herbicides with differentmodes of action as a tank mixtureor sequential application during thesame season.

• Rotate crops. Crop rotation helpsdisrupt weed cycles, and some weedproblems are more easily managedin some crops than others.

• Combine mechanical weed con-trol practices such as cultivationwith herbicide treatments wheresoil erosion potential is less of aconcern.

• Clean tillage and harvest equip-ment to avoid moving weed prob-lems from one field to the next.

Herbicide-TolerantCorn Hybrids

Crops traditionally susceptible tosome herbicides have been developedand are now available that are toler-ant to specific herbicides. Herbicidetolerance in crops results from two dif-ferent procedures: 1) selection by tra-ditional plant breeding methods and2) biotechnology techniques. Ex-amples of corn hybrids includeClearfield corn tolerant toimidazolinone-type herbicides (i.e.,Lightning or Pursuit); RoundupReadyTM corn hybrids tolerant toglyphosate (Roundup, Touchdown,etc.); Liberty LinkTM hybrids tolerantto glufosinate (Liberty); and PoastProtected corn hybrids (see Table 4).

Herbicide-tolerant crops provideadditional options to control someweed problems. However, there areconcerns associated with their use.These include a) misapplication to anormal or traditional crop hybrid, b)drift to nearby susceptible vegetation,c) greater selection for resistant weedspecies or shifts in weed populations,d) herbicide-tolerant crops becomingweedy and difficult to control, e) mar-keting issues, and f) negative publicreaction to biotechnology-derivedcrops. Herbicide-tolerant crops do re-quire greater management to preventproblems such as misapplication, spraydrift, or further development of weedresistance.

Table 4. Herbicide-tolerant corn hybrids and method of development.

Yearreleased Herbicide-tolerant corn Herbicides

Method of development

1992 Imidazolinone Tolerant (IT) andResistant (IR) (also known asClearfield or IMI-hybrids)

Pursuit,Lightning

Plant breedingtechniques

1995 Poast Protect hybrids Poast, Poast Plus

Plant breedingtechniques

1997 Liberty Link hybrids Liberty,Liberty ATZ

Gene insertion

1998 Roundup Ready hybrids Roundup Ultra,ReadyMaster ATZ,Touchdown, and severalother glyphosateproducts.

Gene insertion

Other InformationThis publication explains general

concepts of weed management incorn. More specific information onherbicides and their use in corn canbe found in University of KentuckyExtension bulletin Weed Control Rec-ommendations for Kentucky Farm Crops(AGR-6), revised annually. A com-puterized decision aid (WeedMAKII—Weed Management Applicationsfor Kentucky), which is designed torank treatment options for weed prob-lems in corn and soybean, is anothersource of information for Kentuckycorn producers and crop consultants.Information about these referencematerials can be obtained throughyour local county Extension office orthe University of Kentucky Agricul-tural Distribution Center.

This table should be used only as aguide. Information presented in thistable is the relative burndown responseof emerged plants to herbicides appliedat normal rates for no-till corn. Thisinformation generally does not reflectsoil residual effects of the herbicides.The relative response values are basedon a numerical scale from 0 to 9 andcompare effectiveness of herbicides tocontrol a particular cover crop or weedspecies. A herbicide may perform bet-ter or worse than indicated in the tabledue to weed size or environmental con-ditions or when tank mixed with otherherbicides. If farmers are achieving sat-isfactory results under individual con-ditions, they should not necessarilychange products as a result of informa-tion in this table.

33

Disease ManagementPaul Vincelli

Diseases of crops can occur whenevera disease-causing agent is in contactwith a susceptible host plant in an envi-ronment that is favorable for disease de-velopment. These three fundamentalingredients are necessary for a diseaseto develop and are often referred toas the disease triangle (Figure 1).

Understanding this fundamentalrelationship helps us understand dis-ease management since all diseasemanagement practices presented inthis publication affect one or moresides of the disease triangle. For ex-ample, planting a hybrid with someresistance to gray leaf spot targets thehost side of the disease triangle. Croprotation helps to starve a pathogen (dis-ease-causing agent) by depriving it ofits food source; this affects the patho-gen side of the disease triangle. Delay-ing planting until soil temperaturesexceed 50°F reduces the amount ofseedling damping off by targeting theenvironment side of the disease triangle.

Preplant DecisionsThat Affect DiseaseDevelopment

Most of the agronomic decisionscorn producers make have some im-pact on disease development. In fact,once a corn field is planted, aproducer’s disease management pro-gram is essentially in place, for betteror worse. Thus, consider your preplantdecisions as disease-management de-cisions also.

Crop RotationMany corn pathogens survive be-

tween crops in the corn residue, andsome do not attack other field cropscommonly grown in rotation withcorn. Consequently, rotating to wheat,soybean, or other crops helps to starvecertain corn pathogens that survive inthe field by depriving them of a foodsource as the crop residue decomposes.

Crop rotation is thus one of the mostimportant disease control practices forcorn production worldwide.

Pathogens that are not as effec-tively controlled by crop rotation in-clude those that do not survive in theproduction field itself. For example,rust fungi that attack corn overwin-ter south of Kentucky and are blowninto our corn fields each season onwind currents. Pathogens that attacka wide range of field crops are also lesseffectively controlled through rota-tion. For example, the charcoal rotpathogen can attack corn, soybean,and grain sorghum and is not con-trolled through a corn/soybean rota-tion. Likewise, pathogens that persistindefinitely in agricultural soils arenot effectively controlled throughcrop rotation. An example is the fun-gus Pythium ultimum, the most com-mon cause of damping off of corn.

Resistant HybridsOne of the most practical and eco-

nomical means of disease control is toselect agronomically suitable hybridswith adequate resistance to diseasesof concern on your farm. Unfortu-nately, resistance is not available forsome diseases. However, when avail-

DISEASE

favorableenvironment

susceptiblehost

pathogen(cause)

NO DISEASE

favorableenvironment

susceptiblehost

pathogen(cause)

Figure 1. Disease triangle. Disease only develops when three conditions are met: a pathogeninfects a susceptible host under disease-favorable conditions.

able, disease resistance should be thefoundation for economical diseasecontrol.

No single corn hybrid is resistantto all diseases present in Kentucky.Furthermore, the importance andprevalence of corn diseases vary fromone farm to the next and from oneyear to the next. These facts can com-plicate the hybrid selection process.Nevertheless, an informed decisioncan be made by selecting hybrids withresistance to the diseases most likelyto be a problem. Resistance to otherdiseases should be considered on a sec-ondary basis.

When selecting a hybrid, the pro-ducer should recognize that there aredifferent levels of disease resistance.If available, agronomically acceptablehybrids with high levels of resistanceusually provide the best protectionagainst a serious disease outbreak.Hybrids may also exhibit moderate oreven low levels of resistance to par-ticular diseases. This means that,while the disease still can develop onthese hybrids, lower incidence of dis-ease can be expected in most circum-stances than on a fully susceptiblehybrid. For some diseases, low to mod-erate resistance is all that is available

34

among current commercial hybrids,even though higher levels of resis-tance would be desirable. In thesecases, use of a hybrid with even a lowlevel of resistance is usually superiorto planting a susceptible hybrid.Sometimes a moderate level of resis-tance is acceptable for fields where re-duced disease pressure is expected.However, under high disease pressure,low to moderate levels of disease re-sistance will not provide adequate dis-ease control. Such hybrids mayrequire you to pay greater attentionto other disease management strate-gies in order to achieve good results.

Hybrids can also be selected fortolerance—the ability to yield welleven though symptoms develop. In-formation on disease-tolerant hybridsis limited, but tolerant hybrids can beuseful when available.

It is important to plant more thanone corn hybrid on your farm. Plant-ing one hybrid is like “putting all youreggs in one basket.” Should a diseaseproblem develop on that hybrid, yourwhole crop is at risk. Planting severalhybrids helps to spread the risk of lossesfrom disease.

TillageConservation tillage systems pro-

vide for less soil erosion, less fuel con-sumption, savings of time and labor,moisture conservation, and easierdouble-cropping. Conservation tillagesystems can, however, increase pres-sure from certain diseases, especiallyunder continuous corn production.Prime examples are gray leaf spot andDiplodia ear rot. Spore levels of thefungi that cause these diseases arehigher in fields where previously in-fected corn residue is left on the soilsurface. When residue is tilled into thesoil, spores are trapped undergroundand cannot easily spread toaboveground plant parts. Further-more, buried crop residues decomposefaster, which reduces pathogen sur-vival. Activity of seedling diseases canalso be increased in no-till systemsbecause soils remain cooler and wet-

ter during spring under conservationtillage.

While conservation tillage systemsmay favor certain diseases, they canalso reduce pressure from certain oth-ers. For example, charcoal rot, whichis favored by high soil temperaturesand low soil moisture early in thegrowing season, would be expected tobe worse in a conventional systemthan a no-till system.

The possibility of enhancing pres-sure from certain diseases under con-servation tillage is not necessarily anargument to return to conventionaltillage. However, producers shouldrecognize situations when their pro-duction system may enhance diseaseactivity so they can employ other dis-ease management practices in orderto maintain adequate levels of diseasecontrol.

Other Cultural PracticesOther preplant decisions can also

influence disease activity. For ex-ample, early planting tends to en-hance activity of Pythium seedlingdiseases, which are favored by cool,wet soils. Conversely, late plantingcan enhance pressure from gray leafspot, a late-season disease that is moredamaging on younger crops than moremature ones.

Plant populations are usually se-lected on the basis of hybrid charac-teristics and yield potential of the field.Some diseases can be more severe athigh plant populations; several of thestalk rot diseases are examples. A fer-tility program that is inadequate orexcessive, or in which major nutrientsare not in proper balance, may alsoenhance disease activity.

FungicidesEssentially all corn seed is treated

before purchase with fungicides to helpcontrol seed rots and seedling diseases.This provides inexpensive protectionagainst stand loss, should conditionsfavor these diseases after planting. Un-treated seed should be treated with fun-gicides before planting.

Foliar sprays of fungicides may beeconomical in seed corn fields to pro-tect against a variety of leaf diseases.They may also occasionally be justi-fied for production of certain specialtycorns. However, fungicide sprays typi-cally do not show justifiable economicreturns for commercial production ofdent corn.

Scouting for DiseasesWhile it is not possible to know

with complete certainty which dis-eases will develop in a given season,the disease history of the farm andarea will indicate the diseases mostlikely to occur. A disease history for afarm is established by scouting fieldsand identifying disease outbreakswhen they occur. Your county Exten-sion agent, farm supply dealer, andcrop consultant can also be goodsources of information. However,farm-specific information obtainedthrough field scouting is the most re-liable basis for developing a farm dis-ease history. Unless you are absolutelycertain as to the cause of a particularproblem, have the condition diag-nosed by a reputable field specialist,or submit the sample to the Univer-sity of Kentucky Plant Diagnostic Lab.

MycotoxinsSeveral mycotoxins—toxins pro-

duced by fungi—can occasionally befound in shelled corn. Aflatoxins oc-cur very infrequently in Kentucky, butwhen they occur, they are often asso-ciated with hot, dry weather duringgrain fill or with improper storage con-ditions. Fumonisins can also sometimesbe found in Kentucky corn, as canvomitoxin (also called deoxynivalenol,or DON), and zearalenone. More in-formation on mycotoxins in corn canbe found in the Extension publicationsAflatoxins in Corn (ID-59) and Myc-otoxins in Corn Produced by FusariumFungi (ID-121).

35

Diseases of CornAnthracnose

Cause: Colletotrichum graminicolaSymptoms: Tan to brown leaf spots

surrounded by a yellow halo, usuallymore abundant toward leaf tip. Le-sions may coalesce, blighting entireleaves. Early in season, anthracnosesymptoms are most common on lowerleaves. Late in season, symptoms ofanthracnose include blighting of up-per leaves and possibly breakage ofplant tops (see Top Dieback). Anthra-cnose also causes a late-season lowerstalk rot. Black spines may be visiblein dead leaf spots with a hand lens.

Damage: Early-season leaf symp-toms usually are not damaging but in-dicate the need to scout later for stalkrot. Yields can be reduced from leafblighting, although this is uncommon.The stalk rot phase can cause stalklodging.

Key Features of Disease Cycle: Thefungus survives in undecomposed cornresidue. Spores are spread by wind-blown rain and rainsplash.

Management: Use resistant hybrids,especially where corn is grown with-out rotation under reduced tillage. Ro-tate away from corn for one to twoyears.

Ear and Kernel RotsCause: Stenocarpella, Gibberella,

Fusarium, Aspergillus, PenicilliumSymptoms: Moldy growth on ears

and kernels. Helpful distinguishingfeatures:• Diplodia ear rot, caused by

Stenocarpella—white mold growthbetween kernels, usually progress-ing from base of ear.

• Gibberella—pink to reddish moldgrowth, often progressing from eartip.

• Penicillium—green or blue-greenpowdery mold on and between ker-nels, often at the ear tip.

• Aspergillus—greenish-yellow moldon and between kernels.

• Fusarium—whitish pink to laven-der mold growing on individualkernels or small clusters of kernels.Damage: Ear and kernel rots reduce

feed value and marketability. Yield andtest weight may also be reduced. Whensevere, Diplodia ear rot can affect 50percent or more of the ears in a field.Contamination of grain by mycotox-ins from certain ear molds can also re-duce nutritional value and mar-ketability of the corn. Aspergillus cancontaminate grain with aflatoxins, al-though this toxin is very uncommonin Kentucky. Fusarium verticillioides(=Fusarium moniliforme) and relatedfungi can produce fumonisins in thegrain, and Gibberella can contaminatethe grain with vomitoxin (=DON or

Anthracnose leaf symptoms. (R. Stuckey)

deoxynivalenol), zearalenone, or both.Key Features of Disease Cycle:

Wounds made by birds and insectsprovide infection sites for these fungi,although infection may occur in un-wounded tissues. Other factors thatcan aggravate ear and kernel rots in-clude lodging of stalks that brings earsin contact with soil, incomplete cov-erage of ears by husks, and maturationof ears in upright position.

Management: For Diplodia ear rot,rotate away from corn when 2 to 3 per-cent of ears have the disease; breakup corn residue if practical to enhancedecomposition; and avoid highly sus-ceptible hybrids. For all ear and ker-nel rots, choose hybrids in which earsare well covered by husks and inwhich ears point downward at matu-rity. Control insects that feed on earsin the field. Harvest at about 25 per-cent moisture for shelled corn to mini-mize kernel damage and field losses.Adjust harvesting equipment forminimum kernel damage and maxi-mum cleaning. Avoid harvestingfaster than drying facilities can oper-ate effectively. Dry shelled grain tobelow 15.5 percent moisture within24 to 48 hours after harvest. Cleanbins before storage and maintain drystorage conditions. Control insect in-festations in storage. Periodically aer-ate and check for heating, crusting,or musty odors. Maintain stored cornuniformly as indicated in Table 1.

Table 1. Recommended temperatures for stored corn.

Averagemonthly

temperature

Minimumgrain

temperature

Maximumgrain

temperature

Below 40˚ F 35˚ F 45˚ F

40˚ - 60˚ F Within 5˚ F ofaverage monthly

temperature

Within 5˚ F ofaverage monthly

temperature

Above 60˚ F 55˚ F 65˚ F

36

Gibberella ear rot. (D. G. White)Diplodia ear rot. (P. Vincelli)

Aspergillus ear rot. (R. Stuckey)Fusarium ear rot. (R. Stuckey)

Sources of Additional Information:Principles of Grain Storage (AEN-20),Aeration, Inspection, and Sampling ofGrain in Storage Bins (AEN-45), Afla-toxins in Corn (ID-59), Mycotoxins inCorn Produced by Fusarium Fungi(ID-121).

Gray Leaf SpotCause: Cercospora zeae-maydisSymptoms: Gray to tan, narrow,

rectangular lesions 1/4 to 2 inches long.Lesions on some hybrids exhibit a yel-low border. Lesions are restricted byveins. Substantial numbers of leaf le-sions usually do not appear until tas-seling or later. Older leaves areaffected first; severely affected leavescan be killed when lesions coalesce.Weakening and lodging of stalks mayoccur if a severe outbreak blights

leaves during grain fill.Damage: Yield is reduced through

shorter ears and smaller kernels. Yieldlosses in the range of 10 to 20 percentare typical in susceptible hybridsgrown in Kentucky, although losses of50 percent or more may occur undervery high disease pressure. Test weightmay also be reduced. When leafblighting is severe, stalks may weakenand lodge as the plant draws nutrientsfrom the stalk to fill ears.

Key Features of Disease Cycle: Thefungus survives for one to two yearsin undecomposed residue of infectedleaf blades and sheaths. Spores arespread by air movement. Leaves be-come infected during prolonged peri-ods (11 to 14 hours or more) of highrelative humidity (>95 percent) andwarm temperatures (72° to 86°F). The

disease is most severe in fields withcorn following corn under conserva-tion tillage. Severe yield loss can oc-cur when leaves become blightedduring early grain fill.

Management: Use resistant hybrids,especially when grown without rota-tion under conservation tillage. Rec-ognize that there are no immunehybrids, although hybrids exist witha wide range of levels of partial resis-tance. Typically there is a greaterchoice of resistant hybrids amongmid- and full-season hybrids thanamong early-maturing hybrids. Con-sider using a hybrid with high levelsof resistance in fields where 1) lastyear’s crop was corn, or 2) corn wasgrown two years ago and residue coveris at least 30 percent, or 3) there isuntilled corn residue within 150 to

37

Key Features of Disease Cycle: Thefungus survives in undecomposed cornresidue. Spores are spread by air cur-rents. Spores germinate and infectleaves during wet weather with mod-erate (64° to 81°F) temperatures. Se-vere yield loss can occur when leavesbecome blighted during early grainfill. More severe in fields with cornfollowing corn under reduced tillage.Also infects sorghum.

Management: Use resistant hybrids,especially when grown without rota-tion under conservation tillage. Hy-brids with either single-gene (Ht) ormultiple-gene resistance are available.Rotate away from corn and sorghumfor one to two years.

RustsCause: Puccinia sorghi, Puccinia

polysoraSymptoms: Pustules that are circu-

lar to oval, golden-brown to cinna-mon brown, up to 1/8 inch long.Pustules become brown to black atharvest. Leaves turn yellow and dryup when severely infected. Pustules ofcommon rust (P. sorghi) are commonon both leaf surfaces. Pustules ofsouthern rust (P. polysora) are denselyscattered on upper leaf surface withfew on lower surface.

Damage: Common rust rarelycauses economic loss in field corn inKentucky. An aggressive outbreak ofsouthern rust in late-planted cropsmay reduce stalk strength in a graincrop and quickly desiccate silage corn.

Gray leaf spot on a susceptible hybrid. (D. G. White)

500 feet of the field to be planted (thelater the planting, the further itshould be from untilled corn residueif it is a susceptible variety). Fungi-cidal control of gray leaf spot may oc-casionally be economically justified incertain fields of specialty corns. How-ever, fungicide sprays usually do notshow justifiable economic returns forcommercial dent corn production.

Sources of Additional Information:Gray Leaf Spot of Corn (PPA-35).

Northern Leaf BlightCause: Setosphaeria turcica (=

Exserohilum turcicum, = Helmintho-sporium turcicum)

Symptoms: Elliptical, grayish-greenor tan lesions 1 to 6 inches long withsmooth margins. During dampweather, greenish-black fungal sporu-lation is produced in lesions. Olderleaves are affected first. Severely af-fected leaves can be killed when le-sions coalesce. On hybrids carrying anHt2 resistance gene, long, yellow totan lesions with wavy margins and nosporulation are observed on leaves in-fected with S. turcica. These resis-tance-reaction lesions can be easilyconfused with Stewart’s wilt.

Damage: Yield and test weight canbe substantially reduced in cool, wetsummers, although most hybridsgrown in Kentucky have adequate re-sistance.

Northern leaf blight on a susceptible hybrid. (D. G. White)

Key Features of Disease Cycle: Sporesof both fungi are carried on springtimewinds from southern areas of theUnited States. Common rust is activeduring cool (60° to 75°F), humidweather; southern rust is most activeduring warm (80°F), humid condi-tions. Both fungi infect leaves whenspores are present and leaf surfaces arewet. Both are potentially more severein late plantings. Greatest yield lossoccurs in susceptible hybrids when out-breaks begin during early grain fill.

Management: Most hybrids in Ken-tucky have adequate resistance levelsto common rust for our conditions. Re-sistance to southern rust is limited inhybrids commonly grown in Kentucky.Southern rust outbreaks, when theyoccur, develop in late summer. There-fore, minimize late plantings, whichwould be at a younger age and there-fore more subject to yield loss shouldan outbreak occur.

Common rust (left) and southern rust (right).(D. G. White)

38

Seed Rot and Damping OffCause: Principally Pythium ul-

timum, but also Stenocarpella,Fusarium, Penicillium, Rhizoctonia

Symptoms: Rotting of seed beforeor after germination. Yellowing, wilt-ing, and death of leaves of emergedplants. Soft rot of stem tissues. Rot-ting of roots, which may appearbrown, watersoaked and grayish,faintly pink, or greenish-blue. Mayresult in uneven stand height later inseason.

Damage: Stand establishment andearly-season vigor can be reduced,leading to lower yields.

Key Features of Disease Cycle: Thesepathogens are common fungi in Ken-tucky soils. They usually do not limitstands but can do so when seedlingsare stressed. Common stresses includeplanting in cool, wet soils and chemi-cal injury. Early planting dates pre-ferred by many farmers tend toenhance these diseases.

Management: Use high-quality, vig-orous seed treated with fungicide.Plant in warm (above 50°F), moistsoils; measure soil temperature at a 2-inch depth after sunrise. Place herbi-cide, fertilizer, insecticide, and seedproperly to avoid stress or injury toseedling.

Southern Leaf BlightCause: Cochliobolus heterostrophus

(=Bipolaris maydis, =Helminthosporiummaydis)

Symptoms: Elliptical, tan to lightbrown, small lesions (1/8 to 1/4 inch by1/4 to 3/4 inch), often with somewhatparallel sides, and sometimes with abrown border. Older leaves are af-fected first; severely affected leavescan be killed when lesions coalesce.

Damage: Yield and test weight canbe reduced, although most hybridshave adequate resistance for our con-ditions.

Key Features of Disease Cycle: Thefungus survives in corn residue. Sporesare spread by air currents. Spores ger-minate and infect leaves during warm(68° to 90°F), wet weather. More se-vere in fields with corn following cornunder reduced tillage. Greatest yieldloss can occur when leaves becomeblighted during early grain fill.

Management: Plant resistant hy-brids, especially when grown withoutrotation under reduced tillage. Rotateaway from corn for one to two years.

Smut, CommonCause: Ustilago maydisSymptoms: Greenish-white or sil-

very galls, or swellings, up to 6 inchesin diameter. Galls can occur on anyaboveground plant part. As galls age(except those on leaves), the interiordarkens and turns into masses of pow-dery, dark olive to black spores. Gallson leaves usually remain small (0.5inch or less) and become hard and drywithout rupturing. Plants with galls onthe lower stalks may be barren or pro-duce small ears.

Damage: Hybrids of field corngrown in Kentucky typically have ad-equate resistance, and consequently,yield losses typically are minimal (2percent or less) to nonsignificant.

Key Features of Disease Cycle: Thefungus survives for several years asspores in corn residue and in soil.Spores can infect any actively grow-ing aboveground plant part. Wound-ing (stinkbugs or other forms ofinjury) enhances infection substan-tially. Once infection occurs, galls de-velop, enlarge, turn powdery, andrupture to release spores.

Management: Use hybrids with ad-equate resistance.

Symptoms of Pythium root rot. The outerroot cylinder appears watersoaked and easilyis pulled away from vascular tissue. (D. G.White)

Common smut. (R. Stuckey)

Southern leaf blight. (D. G. White)

39

Stalk RotCause: Stenocarpella maydis

(= Diplodia maydis), Gibberella zeae(= Fusarium graminearum), Fusariumverticillioides (= Fusarium moniliforme),Macrophomina phaseolina, Colleto-trichum graminicola

Symptoms: Lower stalk is spongy andinternal tissue (pith) shredded and of-ten discolored. Stalks weaken andlodge. Plants sometimes turn grayish-green and dry prematurely during grainfill. Helpful distinguishing features:• Diplodia stalk rot, caused by

Stenocarpella—Stalk and pith lightbrown. Small, dark-brown to blackpimple-like fruiting structures de-velop just below epidermis nearbase of stalk.

• Gibberella—Pith pink to reddish.Small black pimple-like fruitingstructures develop superficially onstalk near nodes and can be easilyscraped off with fingernail.

• Fusarium—Pith whitish-pink tosalmon-colored. Roots often rot-ted. Difficult to distinguish fromGibberella.

susceptible than full-season hybrids.Several stalk-rot fungi also cause earand kernel rots. Colletotrichum alsocauses anthracnose of leaves, as wellas top dieback. Macrophomina also in-fects sorghum and soybean.

Management: Use hybrids resistantto stalk rots and important leaf diseaseslike gray leaf spot. Avoid excessiveplant populations. Maintain balancedsoil fertility and adequate but not ex-cessive nitrogen. Control insects thatfeed on leaves, stalks, and roots. Scoutfor stalk rots by either pinching thelower two or three stalk internodes orby pushing stalks 8 to 12 inches fromvertical to check for lodging. Harvestearly if 10 to 15 percent show disease.Avoid growing continuous corn. Con-sider avoiding soybean and sorghumfollowing severe outbreaks of charcoalrot.

Sources of Additional Information:Corn Stalk Rots (PPA-26).

• Charcoal Rot (Macrophomina)—Pith contains many very tiny blackfungal structures, giving charredappearance. Roots rotted and black.

• Anthracnose (Colletotrichum)—Dark brown to black discolorationon exterior of lower stalk. Darkspines may be visible with handlens, especially near soil line. Pithlight to dark brown.Damage: Plants lodge and become

difficult or impossible to harvest. Insevere cases, grain yield may be re-duced.

Key Features of Disease Cycle: Thesefungi survive on corn residues. All butcharcoal rot are favored by warm, wetweather during grain fill. Charcoal rotis favored by hot, dry weather duringgrain fill. Other aggravating factors:• High plant populations.• Loss of leaves from disease, insects,

or hail.• Excessive nitrogen, especially when

combined with low potash.Early-season hybrids are often more

Diplodia stalk rot. (R. Stuckey)

Gibberella stalk rot. Note pink to reddishdiscoloration in pith. (D. G. White)

Gibberella stalk rot. Note fruiting structureson thumbnail. (D. G. White)

40

Stewart’s WiltCause: Pantoea stewartii (=Erwinia

stewartii)Symptoms: Long (2 to 10 inches),

linear (1/8 to 1 inch wide) leaf lesionswith very wavy margins. At first, le-sions are pale green to yellow, but theybecome light brown when they dry.Severely affected leaves are killed.Lesions of Stewart’s wilt are easilyconfused with lesions on hybrids car-rying an Ht2 resistance gene to north-ern leaf blight. To aid field diagnosis,hold leaves to light and look in le-sions for scratch-like feeding marks offlea beetle; if uncertain, submitsamples to the University of KentuckyPlant Diagnostic Labs. Infection ofseedlings causes rapid wilt and death.

have not been commonly reported inKentucky in recent years. Stalk lodg-ing may occur.

Key Features of Disease Cycle: Thefungus survives in corn residue. Sporesare spread by windblown rain andrainsplash. Also causes early-seasonanthracnose on leaves, as well as an-thracnose stalk rot.

Management: Use resistant hybrids,especially when grown without rota-tion under reduced tillage. Rotateaway from corn for one to two years.

Damage: Yield and test weight canbe reduced in susceptible hybrids, al-though most hybrids of dent cornhave adequate resistance. In a highlysusceptible variety, stands may be re-duced if infected as seedlings.

Key Features of Disease Cycle: Over-winters in body of corn flea beetle,which also spreads the bacterium. Dis-ease pressure is usually high in Ken-tucky but can be low following a verycold winter, which kills overwinter-ing flea beetles.

Management: Plant resistant hy-brids. Control of the disease in fieldcorn through application of insecti-cides targeting the flea beetle is un-economical.

Sources of Additional Information:Stewart’s Wilt of Corn (PPA-33).

Top Dieback (Upper Stalk Rot)Cause: Colletotrichum graminicolaSymptoms: Plants turn yellow or red

from top downward during grain fill.Leaves at ear level remain green.Lodging and breakage of stalks occurwhen severe. Internal stalk tissue hasbrown discoloration. Be sure to ruleout stalk injury from European cornborer.

Damage: Yield and test weight canbe reduced, although serious out-breaks of this phase of anthracnose

Stewart’s wilt. (D. G. White) Top dieback. (R. Stuckey)

Anthracnose stalk rot. (D. G. White)Charcoal rot. (D. G. White)

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Virus ComplexCause: Maize Dwarf Mosaic Virus

(MDMV), Maize Chlorotic Dwarf Vi-rus (MCDV)

Symptoms: Symptoms can be vari-able. MDMV typically causes stunt-ing and irregular, light and dark greenmosaic patterns in the leaves, espe-cially the youngest leaves. MCDVtypically causes stunting, yellowing,and sometimes reddening of theyoungest leaves and sometimes causesleaf tattering. Usually most severearound areas of fields highly infestedwith johnsongrass rhizomes.

Damage: Yield and test weight canbe reduced substantially in localizedoutbreaks in and around areas withrhizome johnsongrass.

Key Features of Disease Cycle: Bothviruses overwinter in johnsongrassrhizomes. MDMV is spread by certainaphids; MCDV, by certain leafhop-pers. Late-planted fields have greaterrisk of serious disease outbreaks. Com-

pared to corn planted on time, late-planted corn is at an earlier stage ofcrop development when insect vec-tors become active. Earlier infectionusually results in more severe symp-toms. MDMV also causes a disease ofsorghum.

Management: Use virus-toleranthybrids in fields with heavy infesta-tions of johnsongrass rhizomes. Elimi-nate johnsongrass rhizomes to reducedisease pressure. Avoid late plantingsince the younger a crop is when anoutbreak occurs, the more yield lossis possible.

Sources of Additional Information:Virus Diseases of Corn in Kentucky(PPA-40).

AcknowledgmentThanks to Donald Hershman for re-viewing a previous draft of this chap-ter and to Donald G. White andRichard Stuckey for providing photos.

Virus complex. (P. Vincelli)

42

Insect PestsRic Bessin

Lepidoptera larvae, species differ insensitivity to the Bt protein.

Producers using pest-resistantbiotech crops must use recommendedresistance management strategies be-cause pests may have a high potentialto develop tolerance to crops contain-ing Bt. It is the producer’s responsi-bility to use approved resistancemanagement practices when usingbiotech crops.

Pest MonitoringProcedures

To monitor for insect pests in corn,random sites are selected in the inte-rior of fields. Scouting methods willdiffer among the key pests. The num-ber of sites depends on the size of thefield. In fields of fewer than 25 acres,three sites are needed. In larger fields,add one site for each additional 10acres. Use recommended scoutingmethods for specific pests so thatscouting information can be com-pared with the established treatmentguidelines.

Key FactorsPlanting date and spring weather

conditions to a large part determinethe potential for insect damage tocorn. Southwestern corn borer, Euro-pean corn borer, fall armyworm, andcorn earworm are generally more dam-aging to late-planted corn. Typically,corn planted after May 10 in West-ern Kentucky and after May 20 inCentral Kentucky is at greater risk tosustain economic losses from thesepests. Very early planted corn may ex-perience greater first generation Eu-ropean corn borer activity but willusually escape damage by the secondgeneration. Cool weather conditionsand low soil temperatures after seed-ling emergence may expose youngplants to cutworm and flea beetle

To manage insect pests of corn, pro-ducers have a large number of effec-tive options including preventivecultural controls (such as rotation),insecticides, and resistant hybridsfrom natural and biotech sources. Thechallenge for producers is to selectonly the insect management tools thatare needed to prevent economiclosses. Producers use crop growth in-formation, pest intensity levels anddevelopment stage, pest history,weather conditions, grain price, ex-pected yield, and cost of the controlto determine the need for action.

Insect Resistance throughBiotechnology

Agricultural biotechnology is pro-ducing highly effective tools to man-age troublesome corn insect pests.These hybrids use various genes fromthe soil bacterium Bacillus thuringiensis(Bt) to produce proteins that disruptthe digestive system of certain insectpests. These Bt proteins are very se-lective, i.e., each one will affect onlyspecific groups of insects. These pro-teins are nontoxic to mammals andother animals. Biotech hybrids areavailable that control European andsouthwestern corn borer and suppressfall armyworm and black cutworm. Inthe near future, other types may beavailable that provide control of cornrootworm and enhanced control ofblack cutworm.

In the case of Bt corn, to kill a sus-ceptible insect, a part of the plant thatcontains the Bt protein (not all partsof the plant necessarily contain theprotein in equal concentrations) mustbe ingested. Within minutes, the pro-tein binds to the gut wall and the in-sect stops feeding. Within hours, thegut wall breaks down and normal gutbacteria invade the body cavity. Theinsect dies of septicaemia as bacteriamultiply in its body. Even among

damage over an extended period.Greater attention should be paid tomonitoring plants for seedling pestsduring these growing conditions.

Major PestsBlack Cutworm

Cutworms are potentially very de-structive but are unpredictable, andthe chances of significant damage inany given year are relatively low. Corncan be seriously damaged by cutwormsfrom planting through mid-June whilethe plants are less than 18 inches tall.Serious losses are often associated withwet springs that have caused a delayin planting or during periods of coolweather. Cutworms feed mostly atnight and hide during the day underclods of soil or in burrows below thesoil surface. They cut off the seedlingsat or just below the soil surface. Thepotential for cutworm infestations isinfluenced by late planting, low andwet areas of the field that drain poorly,and fall and early season weed growth.Preventive treatments made at plant-ing may or may not provide sufficientcontrol. A rescue treatment may benecessary for moderate to heavy in-

Black cutworm.

43

festations even when a preventivetreatment was used. Early land prepa-ration and weed control help to re-duce cutworm problems becauseinfestations usually develop on earlyseason weed growth. Control weedsat least 2 weeks before planting.

Scouting ProceduresDescription: Cutworms vary from

dark greasy-gray to black. They havea lighter colored stripe down themiddle of the back, smooth skin, anda brown head capsule. Cutworms mayreach 13/4 inches in length. Cutwormscommonly coil up into a “C” shapewhen disturbed.

Damage: Small larvae chew smallholes in leaves; large larvae chew intothe base of seedlings, cut small plants,and may pull plant parts into the bur-row. Symptoms are wilted or cutplants.

When to monitor: Corn should bemonitored for cutworms at least twicea week for the first 3 to 4 weeks afterseedling emergence.

How to scout: Begin making countswhen wilted or cut plants are first ob-served. Examine 20 consecutiveplants and record the number of cut-worm-damaged plants. Look for livecutworms near damaged plants as theyhide during the day. Dip up an area 3inches in radius around the base of a

damaged plant. Note the number andsize of cutworms.

Economic threshold: 3 percent ormore cut plants and 2 or more livelarvae, 1 inch or smaller, per 100plants. If conditions are borderline,check field again in 24 to 48 hours.

Corn Flea BeetleFlea beetles are among the first in-

sects to feed on emerging corn. Thesebeetles overwinter as adults near cornfields and are active in weeds early inthe spring. Populations are generallyhighest following mild winters. Thesevery small, dark insects jump readilywhen disturbed; hence the name fleabeetles. Flea beetles are important incorn for two reasons. First, they areleaf feeders and large infestations cankill small seedlings. Feeding by thesebeetles results in scarring of the leafsurface that appears from a distanceas frost injury. Serious damage canoccur on plants less than 6 inches tall.Most hybrids will recover from mod-erate levels of flea beetle damage un-der good growing conditions. Controlis rarely justified, unless damage is ex-tensive and growing conditions arepoor. Early feeding often occurs dur-ing cool weather when corn growthis retarded. Second, flea beetles arealso vectors of Stewart’s wilt, alsoknown as bacterial leaf blight. Selec-

tion of corn varieties resistant to thisdisease should be considered.

Scouting ProceduresDescription: Corn flea beetles are

very small, dark insects that jumpreadily when disturbed.

Damage: These beetles are leaffeeders. They make small feeding scarson the surface giving leaves a gray,frosted appearance. Damage is gener-ally serious on plants less than 6inches tall. Flea beetles transmitStewart’s wilt, also known as bacte-rial leaf blight.

When to monitor: Check cornfrom emergence until 12 inches tall.Flea beetle stress may be great onlate-planted corn. However, early-planted fields may also show notice-able damage.

Economic threshold: Treat onlywhen 50 percent or more of the plantsshow signs of feeding on new leaveswith some leaves turning white orbrown.

Corn RootwormsCorn rootworms can be serious

pests of continuous corn in Kentucky.The typical damage symptom is lodg-ing or “goose-necking” of corn thatmay begin to appear near the end ofthe larval feeding period. The entireroot system may be destroyed by a

Corn flea beetle. Western corn rootworm larva.

44

heavy population pressure. Prunedroots place physiological stress on theplant by reducing water and nutrientuptake that reduces yields, especiallywhen coupled with low moisture orpoor fertility. Emerging corn root-worm beetles feed on green silks, pol-len, and green epidermal layer of cornleaves. While rootworm adults may befound in soybean, alfalfa, or sorghumlate in the growing season, unlike instates farther north, damage by root-worm larvae to corn following thesecrops is rare in Kentucky. Crop rota-tion continues to be the most effec-tive method of controlling rootwormlarval damage. Because most root-worm eggs are laid in corn fields dur-ing the growing season, if corn is notplanted in the field the following year,the hatching larvae are left withoutfood and will starve. Treatment offirst-year corn for rootworm is notnormally needed in Kentucky.

Scouting ProceduresDescription: Corn rootworm larvae

have cylindrical white to cream bod-ies with a brown to black head and apair of small legs on each of the firstthree segments behind the head.There is a small brown or black areaon the top of the last segment. Fullgrown larvae are about ½ inch long.Three species of corn rootwormbeetles are found in Kentucky. Thenorthern corn rootworm adult is palegreen to yellow and about l/4 inchlong. The southern corn rootwormadult (also called the spotted cucum-ber beetle) is about 3/8 inch long. It isyellow-green with 11 conspicuousblack spots on the wing covers. Thewestern corn rootworm beetle is yel-low with three black stripes on thewing covers.

Damage: Larvae feed on corn rootsreducing the uptake of water and nu-trients. High winds may blow downseverely damaged plants. Adultbeetles feed on silks, pollen, andleaves. Large numbers during pollenshed may clip silks and interfere withpollenation. Adult rootworm feeding

on leaves generally does not affectyield.

When to monitor: Monitor for root-worm symptoms from late Maythrough June. Watch for irregulargrowth patterns and plant stress.Monitor for adult rootworms fromonset of silking until silks are brown.Also late-planted corn should be in-spected in the whorl stage for adultbeetles.

How to scout: Dig up a 6-inch cubeof soil containing the root zone ofstressed plants to scout for larvae andtheir damage. Carefully break awaythe soil from around the root zone andlook for rootworm larvae and evi-dence of chewing on the plant roots.To monitor for adults, look for beetlesas you walk through the field. Ifbeetles are active, follow these guide-lines: l) Make counts on 20 plantsfrom each location beginning withrandom selection of the initial plant.Make counts on every third or fourthplant until 20 plants per location areexamined. 2) Rootworm beetles flyreadily when disturbed so approacheach plant carefully. Count the beetleson the ear tip, tassel, leaf surfaces, andbehind the leaf axil.

Economic threshold: There are no ef-fective rescue treatments once symp-toms of rootworm damage begin toappear. Damage by rootworm larvaeindicates the need to rotate to anothercrop next year or to use a soil insecti-cide at planting if planting corn in thatfield next year. Treatment may be nec-essary to control adult rootworms ifsilks are clipped back to l/2 inch or lessbefore 50 percent of plants are polli-nated and five or more beetles arepresent per plant. Counts of northernand western corn rootworm beetles areused to make soil insecticide recom-mendations for the following year. Ifcounts of western or northern or bothtogether approach or reach an averageof 20 beetles per 20 plants (l per plant),the farmer will be advised to use a root-worm insecticide if corn is grown inthis field next year.

ArmywormArmyworm is a sporadic early sea-

son pest that can cause occasionallosses in corn and should be moni-tored in the spring. Infestations usu-ally first develop in fields of smallgrains or in other grass cover crops.In conventional tillage systems, par-tially grown larvae can migrate intocorn fields from grass waterways orwheat fields. Damage is usually firstnoticeable around the field marginsadjacent to these areas. Armywormsusually feed at night and damage cornby chewing leaves. They prefer to feedon the succulent leaves in the whorlfirst. Feeding is usually confined to leafmargins, but occasionally the insectsmay strip the entire plant, leavingonly the midrib of the leaves. Duringthe day, armyworms are found in thesoil or underneath groundcover.

Scouting ProceduresDescription: The full-grown 11/2-

inch armyworm has a greenish brownbody with a thin stripe down the cen-ter and two orange stripes along eachside. The head is brown with darkhoneycombed markings.

Damage: Armyworms usually feedat night and damage corn by chewingleaves. They prefer to feed on the suc-culent leaves in the whorl first. Feed-ing is usually confined to leaf margins,but occasionally they may strip theentire plant, leaving only the midribof the leaves.

When to monitor: Mid-May throughJune. Armyworm damage is often as-sociated with cool, wet spring weatherconditions.

How to scout: In conventional till-age, infestations usually begin aroundthe field margins adjacent to smallgrains or grassy strips. These areasshould be scouted first. If armywormsare present, determine how far the in-festation extends into the field. Tosample for armyworms, examine 20consecutive plants in each of at leastfive random locations in the field.Note the number of plants with thecharacteristic damage and the size of

45

the larvae. When scouting for army-worms, look on the armyworms forparasitic eggs. These small, oval, yel-lowish eggs are usually located justbehind the head of the larva. Theseare eggs of a fly parasite that will killthe larva.

Economic threshold: Control actionsin corn are recommended when army-worms average between ½ and ¾inches and the entire field averages35 percent infested plants or 50 per-cent or more defoliation is seen ondamaged plants. Do not include para-sitized larvae in the counts used to de-termine the economic threshold.

When to monitor: First generation:Late May to early June. Early-plantedcorn has the greatest potential fordamage. Second generation: LateJune to August. Late-planted corn ismost susceptible to this generation.

How to scout: Randomly select 20consecutive plants at each site. For thefirst generation note the number ofplants with fresh damage to leavesemerging from the whorl. Pull thewhorls from two damaged plants andexamine for the presence of borers. Forthe second generation, pay special at-tention to late-planted fields. Exam-ine 20 plants per locations and checkplants for egg masses and signs of feed-ing and larvae feeding on the leaves,tassels, leaf axils, or behind leaf sheaths.

Economic threshold: Treat for firstgeneration if 50 percent or more ofthe plants are infested and live larvaeare present in the whorls. For the sec-ond generation, treatment is recom-mended if an average of one egg massper plant is recorded or if 50 percentof the plants have live larvae feedingon the leaves, tassels, leaf axils, orbehind leaf sheaths. A more compre-hensive economic threshold can befound in European Corn Borers in Corn(ENT-49).

Armyworm moth.

Armyworm.

European corn borer moth.

European corn borer.

European Corn BorerThe corn borer larva tunnels into

corn stalks and ear shanks and feedson kernels in the ear. The severity ofcorn borer infestations varies fromyear to year and even from field tofield on the same farm. First-genera-tion moths are attracted to early-planted corn, while late-planted cornis most susceptible to damage from thesecond generation. Corn borers causedamage in two major ways. First, tun-neling in the stalk reduces water andnutrient flow and contributes tophysiological yield loss. This is theprimary cause of yield reduction. Sec-ond, borers produce cavities in theplant that weaken it. Stalk breakageand ear drop, prior to harvest, canlower yields through harvest losses.These losses increase if harvest is de-layed. Strong winds or driving rainsduring early season moth flight mayreduce corn borer activity for the en-tire season. However, calm, warmnights during the egglaying promoteshigh corn borer populations, even ifthe adult population is relativelysmall. Early harvest can reduce lossesdue to broken or lodged plants ordropped ears. Second-generationdamage is the primary cause of har-vest loss. Early planting combinedwith early harvest can be an effectivemanagement strategy.

Scouting ProceduresDescription: Eggs are creamy white

when first laid and develop a dark spotclose to hatch. Eggs are laid in groupsof 15 to 35 and overlap each othermuch like fish scales. Larvae are pink-ish colored, marked with small roundbrown spots and a faint grey striperunning the length of the back. Theyreach 1 inch when fully grown.

Damage: Small first-generation lar-vae make “window pane” holes inleaves that are noticed as they emergefrom the whorl. Some enter leaf mid-ribs and cause them to break. Largerlarvae tunnel into the stalk. Second-generation damage include feeding onthe stalks, tassels, ear shanks, and de-veloping kernels.

46

Comments: All of the currentlyavailable Bt-corn hybrids provide ef-fective control of first-generation lar-vae, but some do not maintain thislevel of control against the late-sum-mer generations.

Southwestern Corn BorerWhile similar in biology to the

European corn borer, southwesterncorn borer is more difficult to control.It is found in the western part of thestate and has two generations per year.The first generation attacks whorl-stage corn and is associated with lossesto yield by stunting or killing plants.The second generation occurs duringmid- to late summer and increasesharvest losses through stalk breakagedue to extensive tunneling. In the fall,overwintering larvae increase plantlodging by girdling the base of thestalk just above the soil. Early plant-ing, when practical, is generally themost efficient and economicalmethod of preventing plant damageand yield losses to this pest. However,wet weather frequently delays cornplanting and increases the possibilityof borer infestations. Corn plantedafter May 1 has a greater potential forsouthwestern corn borer infestations.Lower establishment rate by second-generation borers on older plants isthe primary reason for early planting.

Scouting ProceduresDescription: Eggs are laid singly or

in groups of two to five, with the flat-tened eggs overlapping like fish scales.Initially eggs are greenish-white butdevelop three distinct red transverselines within 24 to 36 hours. Larvaeare creamy-white with numerous con-spicuous black spots and a brown headcapsule. The full-grown larva is 11/4

inch in length.Damage: For the first 2 weeks, first-

generation larvae feed within thewhorl of the plant; later they tunnelinto the stalk. Numerous holes in theemerging leaves and leaf breakage dueto midrib tunneling are characteris-tic. The second generation causes thegreatest damage. These larvae beginfeeding in the mid and lower zones oftassel-stage corn in mid-to-late July.After about two weeks, the larvae be-gin tunneling in the stalk. Character-istically, they make a straight linethrough the middle of the stalk. In thefall, borers that will remain larvaethroughout the winter migrate to thebase of the plant and girdle the plantat the base before tunneling down-ward. Larvae girdle the stalk by chew-ing a complete or partial internalgroove, leaving only a thin outer layerfor support.

When to monitor: First generation:Late May to the end of June. Early-planted corn has the greatest poten-tial for damage. Second generation:Early July to the end of August. Late-planted corn is most susceptible to thisgeneration.

How to scout: Use the same meth-ods described for the European cornborer.

Economic threshold: Controls forfirst-generation southwestern cornborer should be considered if 35 per-cent of the plants show signs of dam-age and live larvae are present in thewhorls. Control of second generationwith insecticides is difficult because theattack is concentrated low on the stalk.

Comments: All of the currentlyavailable Bt-corn hybrids provide ef-fective control of first-generation lar-vae, but some do not maintain thislevel of control against the late-sum-mer generations. Currently, only theYieldGard hybrids provide the full-season control needed to prevent thestalk girdling caused by the late-sea-son larvae.

Fall ArmywormFall armyworm can be one of the

more difficult insect pests to controlin field corn. Late-planted fields and

Southwestern cornborer. Southwestern corn borer moth.

47

late-maturing hybrids are more likelyto become infested. Fall armywormcauses serious leaf feeding damage aswell as direct injury to the ear. Whilefall armyworms can damage cornplants in nearly all stages of develop-ment, they will concentrate on lateplantings that have not yet silked.Large fall armyworm larvae consumelarge amounts of leaf tissue, resultingin a ragged appearance to the leavessimilar to grasshopper damage. Largerlarvae are usually found deep in thewhorl, often below a “plug” of yellow-ish brown frass. Beneath this plug, lar-vae are protected somewhat frominsecticide applications. Plants mayrecover from whorl damage withoutany reduction in yield. Producersshould pay close attention to late-planted fields; problems are usually as-sociated with fields planted after June1. Some Bt-corn hybrids may suppressthis insect.

Scouting ProceduresDescription: The spherical gray eggs

are laid in clusters of 50 to 150, usu-ally on the leaves. Egg masses are cov-ered with a coating of moth scales or

fine bristles. Larvae hatch in three tofive days and move to the whorl. Lar-vae range from light tan to black withthree light yellow stripes down theback. There is a wider dark stripe anda wavy yellow-red blotched stripe oneach side. Larvae have four pairs offleshy abdominal prolegs in additionto the pair at the end of the body. Fallarmyworm resembles both armywormand corn earworm, but fall armywormhas a white inverted “Y” mark on thefront of the dark head. Fall armywormhas four dark spots arranged in asquare on top of the eighth abdomi-nal segment.

Damage: Small larvae cause elon-gated “window pane” damage toleaves similar to European corn borer.The most common damage is to latepre-tassel corn. Large fall armywormlarvae consume large amounts of leaftissue resulting in a ragged appearancesimilar to grasshopper damage. Largelarvae are usually found deep in thewhorl, often below a “plug” of yellow-ish brown frass. Beneath this plug, lar-vae are protected somewhat frominsecticide applications. Plants oftenrecover from whorl damage without

any reduction in yield. On later stagesof corn, fall armyworm larvae oftenattack the developing ear directly.

When to monitor: Begin monitoringin mid-June. Pay close attention tolate-planted fields or fields with a his-tory of these problems.

How to monitor: Survey 20 con-secutive plants from at least five lo-cations in the field. Examine theplants for egg masses, signs of dam-age, and live larvae in the whorl. Pullthe whorl on two damaged plants todetermine if the larvae are protectedbeneath a frass plug.

Economic threshold: If present indamaging numbers in the field, it mustbe controlled while the larvae are stillsmall. Control needs to be consideredwhen egg masses are present on 5 per-cent of the plants or when 25 percentof the plants show damage symptomsand live larvae are still present. Con-trolling large larvae, typically afterthey are hidden under the frass plug,will be much more difficult. Treat-ments must be applied before larvaeburrow deep into the whorl or enterears of more mature plants.

Western corn rootworm adult. Fall armyworm.

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Economics for Corn ProductionGreg Ibendahl

farm grows 70 acres of corn and 30acres of soybeans or if 30 acres of cornare grown with 70 acres of soybeans.In establishing a cost for the variableinputs, a usage rate per acre is multi-plied by the appropriate price per unit.

The last item for the variable costsis an interest charge. This cost reflectsthe money needed to plant a crop.When the crop is sold, the money isreturned. If the money is borrowed,this is the actual interest expense.When the farmer’s own equity is used,this cost is an opportunity cost sincethe money could have been earninginterest. Usually six months is used asthe time frame for the interest on vari-able costs (i.e., planting to harvest isroughly six months).

The difference between gross re-turns and total expenses is the returnto operator labor, land, capital, andmanagement. The return to operatorlabor and management is compensa-tion for the farmer’s time and exper-tise invested in growing a corn crop.The return to land and capital is anopportunity cost for using the landand other capital. Because the farmerhas equity invested in the land, thosefunds cannot be earning interest in abank or used for other purposes.

Any preexisting budget should beused with care. More than likely, thequantities and prices will need to beadjusted to fit an individual producerin a given year. In Table 1, the priceof corn will almost certainly need tobe adjusted. The interactive budgetfrom the Department of AgriculturalEconomics makes this process easysince it automatically adjusts the com-putations.

Determining prices and quantitiesis probably the most difficult aspect ofbuilding a corn budget. Input pricescan be readily obtained from manyagribusinesses. However, the bestsource for quantity information, is a

Corn producers grow corn to make aprofit. Thus, an understanding ofsome basic economic concepts andtools should help them become bet-ter managers.

Enterprise BudgetsOne of the best tools for planning

purposes is an enterprise budget. En-terprise budgets predict profitabilityby incorporating quantities and pricesof all inputs and outputs. Enterprisebudgets are started by estimating theexpected corn production in bushelsper acre and the expected price re-ceived. These two pieces of informa-tion give the expected gross revenuesper acre. Next, all the expected quan-tities and prices of inputs are listed toprovide the expected expenses peracre. Table 1 shows a typical corn bud-get for Kentucky. This interactivebudget is available from the Depart-ment of Agricultural Economics at theUniversity of Kentucky. The Webaddress is: http://www.uky.edu/Agri-culture/AgriculturalEconomics/data/baledcropbudgetinstr495.html.

The corn budget in Table 1 is di-vided into three main sections: grossreturns, variable costs, and fixed costs.These are all stated on a per acre ba-sis. Gross returns are calculated bymultiplying the expected yield peracre by the expected price. For situa-tions where corn is used by a livestockenterprise, a value is still assigned tothose bushels.

Expenses are divided into variableand fixed costs by whether the ex-pense varies as the size of the enter-prise changes. Most of the expenses,such as seed, fertilizer, chemicals, etc.,vary as the enterprise size varies. How-ever, depreciation, insurance, andtaxes are not dependent on the sizeof the corn enterprise. For example,insurance is the same whether the

farmer’s own records. Good productionrecords can provide information aboutyields and about how much fertilizerand chemicals normally are used.

The Department of AgriculturalEconomics also provides a tool thatcan help a farmer develop his or herown corn budget. This budget genera-tor is the “Corn Cost and Return Es-timator” and is available at: http://w w w . u k y . e d u / A g r i c u l t u r e /A g r i c u l t u r a l E c o n o m i c s / d a t a /baledcorninstr495.html. The tool usesinformation about how the corn isgrown, soil tests, price informationfrom suppliers, etc., to develop a moredetailed corn budget.

Estimates of corn prices are prob-ably more uncertain than the otherestimates. Prices can vary a lot duringthe summer due to weather-relatedevents. Proper marketing can help heretoo. The price on the budget shouldbe the average price received and notthe price at harvest. The price shouldalso reflect any government paymentsthat change in response to enterprisesize. For example, LDP payments, sincethese are tied to production, should beadded to the budget price.

An additional step to enterprisebudget preparation and use is to con-duct sensitivity analysis. The originalnumbers used in the budget wereprobably the producer’s predictions ofnormal yields and prices. However, asmost producers are aware, very fewyears are average. By conducting asensitivity analysis, producers can seethe effects on their incomes by tryingother combinations of yields andprices. At a minimum, a producershould examine a worst case, an aver-age case, and a best case scenario.These results should help farm man-agers do forward planning. In additionto yields and corn prices, producersmight also conduct sensitivity analy-sis of fertilizer and fuel prices.

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Partial BudgetsEnterprise budgets are great for

showing how an enterprise contrib-utes to profitability. However, some-times a producer might be interestedin examining how some adjustmentto an enterprise or combination of en-terprises affects profitability. Examplesinclude growing high-oil corn insteadof conventional corn or replacing soy-bean acres with corn acres. Partialbudgeting is a good tool for these situ-ations because only those costs, in-comes, and resource needs thatchange with a proposed adjustmentare examined. The resources, costs,and income that are not affected withthe proposed change are ignored.

Partial budget analysis is a three-step process. Step one determines

what increases the profits of the farmbusiness when a change is imple-mented. This increase in profitabilitycan come from either greater incomeor less costs. Step two determineswhat decreases the profits of the farmbusiness. A reduction in income andan increase in costs can decrease theprofitability of the farm business. Stepthree determines the net change inprofits. This step compares the in-crease in profits from step one to thedecrease in profits from step two. Ifthe increase in profits are greater thanthe decrease in profits, then thechange should be made.

An example should help clarify theprocess. Consider a farmer looking atreplacing 40 acres of conventionalcorn with 40 acres of high-oil corn.Step one requires the farmer to deter-

mine the increase in farm businessprofits. For step one, the farmer shouldhave greater income from the 40 acresof high-oil. This is calculated as 40acres times yield per acre times pricereceived. Growing high-oil may nothave any reduced costs, so the onlycontribution to step one is the in-crease in income. Step two has thefarmer determining the decreases infarm business profits. Here, there aretwo contributions, less income andmore costs. Reduced income is fromgiving up the 40 acres of conventionalcorn (acres x yield x price). Increasedcosts occur from likely higher costs forseed, transportation, and storage as-sociated with high-oil corn produc-tion. If the benefits from step oneoutweigh the decreases in step two,the farmer should make the switch tohigh-oil corn.

Cost ConceptsInput costs are a concern for many

producers since it seems that the pricesof inputs rise faster than the price ofcorn. Corn producers should be awareof at least two cost concepts, fixed ver-sus variable costs, and long-run versusshort-run costs. The two concepts arerelated and help explain the rationalebehind many farm decisions.

As Table 1 shows, budgets are di-vided into variable and fixed costs.Variable costs change with the vol-ume of corn produced. You can thinkof variable costs as those that themanager has control over at a givenpoint in time. Seed, fertilizer, herbi-cides, fuel and oil, etc., are directlyrelated to how much corn is producedand are directly controlled by themanager. As more of the input is used,more output is produced. However,there is some limit to most inputswhere additional input use does notincrease corn yield. For example, fer-tilizer helps increase yield up to apoint. Once this point is reached, ad-ditional fertilizer may actually de-crease corn yields. At most, a farmmanager would only use a level of theinput until yields are maximized. As

Table 1. Typical corn budget.

Amount Unit Price Total

Gross returns per acre

Corn 125 bu $2.75 $343.75

Variable costs per acre

Seed 0.32 bag $78.00 $24.96

Fertilizer 1 acre $51.90 $51.90

Lime 1 ton $12.12 $12.12

Herbicides 1 acre $20.00 $20.00

Insecticides 1 acre $15.00 $15.00

Fungicides 1 acre $0.00 $0.00

Fuel and oil 2.2 hrs $6.31 $13.88

Repairs 1 acre $22.77 $22.77

Custom application 1 applications $4.12 $4.12

Equipment rental 1 acre $0.00 $0.00

Drying 125 bu $0.11 $13.75

Crop insurance 1 acre $0.00 $0.00

Cash land rent 1 acre $0.00 $0.00

Hired labor 0 hrs $0.00 $0.00

Interest on variable costs (½ year) $178.50 dollars 4.50% $8.03

Total variable cost $186.53

Return above variable cost $157.22

Budgeted fixed costs/acre

Depreciation $40.00

Taxes and insurance $10.00

Total budgeted fixed cost $50.00

Return to operator labor, land, capital, and management $107.22

Less operator labor 4.5 hrs $7.00 $31.50

Return to land, capital, and management $75.72

University of Kentucky, College of Agriculture, Cooperative Extension Service.

Break even price $1.49 per bu to cover variable costs at 125 bu per acreBreak even yield 67.8 bu to cover variable costs at $2.75 per bu

50

shown later, however, the profit-maxi-mizing level of an input is probablybelow the yield-maximizing level ofthat input.

Fixed costs, on the other hand, donot change with the volume of cornproduced. These are the costs incurredeven if the input is not used. Anothercharacteristic of fixed costs is thatthey are not under control of the man-ager. As shown in Table 1, deprecia-tion, taxes, and insurance are all fixedcosts since they must be paid even ifno corn is produced.

The concepts of variable versusfixed costs need to be discussed withinsome sort of time frame. Short-runand long-run are time concepts, butthey are not defined by a specificlength of time. Short-run is definedas a period of time during which oneor more of the inputs is fixed inamount and cannot be changed.Long-run is defined as that period oftime during which the quantity of allinputs can be changed.

These concepts are important be-cause costs that are defined as fixedin the short-run become variable inthe long-run. Likewise, variable costsmay become fixed if the short-run isdefined to be a small enough timeframe. The corn budget in Table 1 usesa short-run time frame of a year. Thus,most of the input costs are variableand can be changed by the farm man-ager. If a long enough time frame wasconsidered, then depreciation, insur-ance, and taxes would also becomevariable since a long enough time

span allows the manager to considerselling assets as part of the decisionprocess.

The short-run versus long-run con-cept is particularly important for thosedecisions where the short-run is a verysmall time interval. In these situa-tions, most of the costs are fixed andonly a few are variable. An exampleis a decision of whether to harvestcorn in a very severe drought year.The short-run decision rule for farmmanagers is to cover variable costs. Ifthe corn has already grown, the onlyvariable costs are harvesting, drying,transportation, and storage. Decisionsabout fertilizer, herbicides, etc., arealready fixed. Thus, as long as thevalue of the corn exceeds these fewremaining costs, the harvest shouldcontinue. Even though the crop maybe so small that not all costs are ac-counted for, at least the variable costsat the time are covered.

Economic ConceptsOne of the basic questions facing

corn producers is how much corn toproduce on an acre. Because farmersare growing corn to make money, theywant to maximize profits per acre.This is probably not the same as maxi-mizing yield. The marginalism prin-ciple is very important for helpingproducers decide on the optimalamount of an input. The basic ideaconcerns the last unit of an input uti-lized or of an output produced. As anexample, the cost of the fertilizer toproduce the last bushel of corn should

be less than the price per bushel. An-other way of looking at this is that thevalue of corn produced from the lastpound of fertilizer used should begreater than the cost of that pound offertilizer.

Figure 1 shows how corn yield re-sponds to N fertilizer. The four pointsin the figure have the following yieldresponses:

Point Kg of nitrogen Kg of corn

A 120 6495

B 150 6917

C 180 7185

D 210 7301

The yield-maximizing point is D;however, this is not the profit-maxi-mizing point. Here’s how themarginalism principle works if corn isworth $2.50 per bushel and N costs$0.20 per pound. For each additional30 pounds of additional N applied, thefarmer pays $6. By increasing yieldfrom point A to B, the farmer earns$17.50 in additional revenue (7 bush-els of corn times $2.50 per bushel).From point B to C, the farmer earns$10 in additional revenue. From pointC to D, the farmer earns $2.50 in ad-ditional revenue. Thus, point C is theprofit-optimizing point. Moving from110 to 140 and from 140 to 170pounds on N is profitable becauseeach 30 pounds of N increases costsless than the value of corn produced.However, the move from 170 to 200pounds of N is unprofitable becausethis 30 pounds of N increases costs $6but only increases corn profits by$2.50.

Figure 1 is for illustration only.Actual corn response to N will dependon many factors such as soil type, dateof N application, N carryover, etc.The point here is that the benefitsfrom the additional input should out-weigh the costs from the additionalinput. These techniques apply to allinputs and not just N fertilizer.

A few general assumptions can bemade about marginalism. The first is

Figure 1. Corn yield response to nitrogen.

5,000

5,500

6,000

6,500

7,000

7,500

0 30 60 90 120 150 180 210 240 270 300 330

Kg of N

Kg

of C

orn

CD

B

A

51

that yield-maximizing goals are not thesame as profit-maximizing goals. Thesecond is that an increase in the costof an input relative to the price of corncauses a producer to use less of thatinput. For example, if N fertilizer in-creases in price while corn does not,then the farmer should use less N. Inaddition, if the corn price increaseswhile the N price stays the same, thenthe farmer should use more N.

Opportunity CostFinally, corn producers should be

aware of opportunity cost. This con-cept was briefly discussed in relationto return to land and capital from theenterprise budgets. Producers areprobably most concerned about ac-counting profits and cash flow. How-

ever, opportunity costs should be con-sidered as well. Producers who provideequity for their farming operationsshould be rewarded for using that eq-uity. That is why the enterprise bud-gets have these returns to equity andmanagement lines.

Opportunity cost can be defined asthe maximum net return that is sacri-ficed because the resource is not em-ployed in its next most profitablealternative. Producers who own theirown land sacrifice the return theycould earn by investing their land eq-uity in the bank. Producers can almostthink of opportunity costs as the costfor borrowing money from themselves.

This concept really is apparent forproducers who own rather than rent.Renters have a rental cost as part of

the enterprise budget, while produc-ers who own will have a zero for therent charge. At first glance, farmerswho own their land might appear tohave a tremendous advantage overrenters, and in some ways they do.Farmland owners will almost certainlyhave greater cash flow and earn largerprofits from a cash accounting per-spective. However, farmland ownersshould be sure to include the oppor-tunity cost of the land when lookingat economic profits.

These are just some of the economicissues that corn producers should con-sider. Proper planning and a good un-derstanding of the true costs of cornproduction should help farmers in-crease their long-term profitability.

52

Corn Harvesting, Handling,Drying, and Storage

Samuel McNeill and Michael Montross

vest period—from the field to the el-evator or miller. Such an investmentin drying and storage facilities man-dates that producers and crop man-agers do a good job of maintaininggrain quality after harvest and keep-ing it in good condition throughoutthe storage period. Otherwise, the po-tential profit from these enterprisesmay be lost.

Preparing for HarvestAll equipment that will contact

corn as it moves from the field to thestorage bin should be thoroughlycleaned prior to harvest to minimizemold and insect infestations and pro-tect the purity of individual corn va-rieties or seed lots. This is especiallytrue for genetically enhanced crops,which should be harvested after non-genetically altered crops to avoid pos-sible/probable mixing. All combines,hauling vehicles, conveyors, dryingequipment, and storage bins should bethoroughly cleaned before the rush ofharvest begins.

Ideal corn varieties have high yieldpotential, high test weight, a sounddisease-resistance package, and strongstalks to avoid lodging problems andrapid dry-down in the field, and theyare disease and insect free at harvest.Less than ideal conditions requiremore management skill to avoid po-tential problems after harvest. Com-bines should be serviced and adjustedaccording to the owner’s manual priorto harvest to assure minimal mechani-cal damage to corn kernels. Cleangrain dryers, perform a routine main-tenance check on the sensors andcontrols, and test fire the unit(s) priorto the beginning of harvest to avoidequipment downtime.

IntroductionDrying and storing corn on-farm

can help producers and farm manag-ers control elevator discounts and im-prove economic returns to theiroperation. The use of such facilitiesrequires operators to maintain grainquality from the field to the point ofsale to capture market premiums.Treatment of grain soon after harvestoften determines the storability of acrop and can strongly influence itsquality when delivered to the end-user—which may be several weeks,months, or even years after harvest.Thus, it behooves grain farmers toimplement sound grain harvest, dry-ing, and storage practices to maintainthe reputation of the United Statesas a reliable supplier of good qualitycorn to the global market. Successfulpost-harvest grain processing with on-farm facilities requires a thorough un-derstanding of the factors thatinfluence grain quality.

On-farm drying and storage facili-ties let producers avoid excessive un-loading times that often plaguecountry elevators during the peak har-vest season. Numerous delaysthroughout a harvest season can in-crease harvest losses for some indi-viduals, especially if insects, disease,or weather threatens their crop dur-ing this period and unusually highstalk lodging problems develop.

Disadvantages of on-farm dryingand storage are the high initial equip-ment costs and additional manage-ment requirements. Drying, handling,and storage equipment can easily costseveral hundred thousand dollars, andthe best way to protect this invest-ment is through prudent managementthroughout harvest and the post-har-

Spray the vegetation around stor-age bins with herbicide and thoroughlyclean out bins prior to harvest to pre-vent creating a harborage for rodentsand insects. Sweep down walls, ladders,ledges, and floors inside grain bins toremove old grain and fine materialwhere insects and mold spores can liein wait to contaminate the incomingcrop. Provide dust protection masks soworkers will avoid potential breathingproblems when cleaning bins andequipment. After mowing and clean-ing, spray a residual pesticide inside thebin to the point of runoff for additionalprotection from insects. Be sure to readpesticide labels carefully for any spe-cific delays prior to filling the bin orother restrictions after application. Itis always a good idea to fumigate thespace under the false floor of grain binsto eradicate that area of insect popula-tions. Don’t confuse residual pesticideswith fumigants, which have no carry-over effect, and keep in mind that fu-migants are toxic to humans and otherwarm-blooded animals and thereforeare Restricted Use pesticides.

Harvest ConsiderationsHarvest should begin when opera-

tors can optimize profits, which is in-fluenced by the price of corn,potential yield, length of harvest pe-riod, weather, and costs for equip-ment, labor, and energy. Some of thesevariables change during the course ofthe harvest season so this is usually avery dynamic situation each year. Op-erators should have a realistic figurefor each of these variables before har-vest begins and should be flexibleenough to compromise between anyconflicting situations. For example,corn usually reaches the maximum dry

53

matter accumulation at a grain mois-ture level of 35 to 38 percent, butmachine losses are usually lower whenshelling corn below 25 percent mois-ture. Consequently, most farmers withdryers opt to begin harvest a littleabove 25 percent moisture with thehope of being able to finish before itdries completely in the field.

The length of the harvest period ishighly dependent on the size of theoperation, combine speed and capac-ity, efficiency of the harvesting-haul-ing-handling-drying-storage system,and weather. Total harvest losses gen-erally increase with the time requiredto gather the crop and can occur frompre-harvest losses and machine losses.Pre-harvest losses can be caused byhigh winds, hail, or similar weatherevent, from disease or insect pressure,or from a combination of these situa-tions. Machine losses are inevitable,so the challenge is to:1. Know where they occur.2. Understand how to measure them.3. Know what to do to correct them.4. Motivate combine operators to

measure these losses and take ac-tion when they reach economicthresholds.

The income gained by reducing ma-chine losses is achieved with verylittle added equipment and labor ex-pense, so the time required to care-fully adjust and operate the combinecan be extremely profitable.

Where Do CombineLosses Occur?

Combine losses can occur duringany of the three main areas of themachine (function in parentheses)—header loss (gathering), rotor or cyl-inder loss (threshing), or fan and shoelosses (cleaning). Table 1 shows typi-cal losses from each machine area foran average and expert operator. Earlosses are intact ears that are left onthe stalk or dropped from the header

after being snapped. Threshing lossesare kernels that remain on the cob dueto incomplete cylinder/rotary action.Loose kernels on the ground can becaused by shelling at the snappingrolls or by an overloaded cleaningmechanism. Differences between op-erators are largely due to combine ad-justments and operation and canobviously impact profitability (4.3bushels per acre in this case). Excesslosses can often be avoided by takinga few minutes to measure them andby making the machine adjustmentsnecessary to correct them.

How to MeasureCombine LossesEar Losses

The first step in knowing whethercombine losses are excessive is to de-termine the total loss behind the ma-chine. Experienced operators canmake this first check in five to 10minutes and should do so when con-ditions change from field to field orwithin a field (different variety, plant-ing date, or grain moisture level).Mark off a 1/100-acre area and lookthrough the residue for whole and bro-ken ears that are loose on the groundand those still attached to stalks. SeeTable 2 for the row length needed tomake up 1/100-acre with different rowwidths and header sizes. Gather allwhole and broken ears in this area andweigh them to the nearest 0.1 pound(1.6 ounces or 35 grams). Each 3/4-pound ear (or equivalent) representsa loss of one bushel per acre.

Table 1. Typical combine losses foroperators with different skills.

Type of loss

Combine losses(% of yield)

Average Expert

Ear loss 4.0 1.0

Threshing loss 0.7 0.3

Loose kernel loss

1.4 0.5

Total loss 6.1 1.8

Table 2. Row length (feet) for 1/100-acre area atdifferent row widths and header sizes.

Row width(inches)

Header size

4 rows 6 rows 8 rows 12 rows

Row length (feet)

20 65.3 43.6 32.7 21.8

30 43.6 29.0 21.8 14.5

36 36.3 24.2 18.2 12.1

If ear losses are more than 1 bushelper acre and many intact ears arefound on stalks, pre-harvest lossshould be measured. Check an adja-cent 1/100-acre area of unharvestedcorn and gather and weigh all ears onthe ground. Figure pre-harvest loss onthe basis of a ¾-pound ear. Subtractpre-harvest loss from header loss. Ifheader loss exceeds 1 bushel per acreconsider reducing ground speed, ad-justing the header height, or snappingrolls to reduce this loss.

Kernel LossesThe first step in measuring loose

kernel loss is to make a frame fromwood, wire, or string that covers a 10-square-foot area (see Table 3 for framedimensions for different row widths).Center the frame over each row be-hind the combine and count kernelsstill attached to broken cobs (thresh-ing loss) and loose kernels lying onthe ground (cleaning loss). A coffeecan is handy to collect a commingledsample from all rows that can be in-spected to assess kernel damage dur-ing threshing. Two kernels per squarefoot are equal to a bushel per acre loss,so divide each count from each rowby 20 to determine threshing andcleaning losses. If the threshing andloose kernel loss is below 0.3 and 0.5bushels per acre, respectively, you arean expert combine operator! If yourlosses exceed these limits, combineadjustments are advised. If separationloss exceeds 0.3 bushels per acre, ad-just cylinder or rotor speed for bettershelling.

54

If loose kernel loss is above 0.5bushels per acre 1 final measurementis needed to determine the problemarea. Stop the combine between theends of the row and back it up about20 feet. Now place the frame overeach row in the area previously underthe header and count loose kernels todetermine header loss. The differencebetween loose kernels counted behindthe combine and those counted un-der the header can be attributed tothe cleaning mechanism (walker andshoe).

Adjustments to ImproveCombine Performance

If excessive harvest losses arefound, it is important to make theright machine adjustments quickly tominimize economic loss. Some prob-lems require the adjustment of a singlecomponent, while others involve sev-eral different areas of the combine. Itis usually best to make small indi-vidual changes one at a time and mea-sure the outcome of that adjustmentbefore more modifications are made.

A ground speed of 2.5 to 3 milesper hour usually produces good results.Position the header accurately overthe rows to feed the material smoothlyinto the gathering chains and snap-ping rolls. Run snouts low enough sothat the ears contact the upper thirdof the snapping rolls. Set snappingrolls according to stalk width andmatch their speed to ground speed toreduce ear loss.

Flights on gathering chains shouldbe opposite each other and shouldextend about ¼ inch beyond thesnapping bar. Chain speed should beset to guide stalks into the rolls with-out uprooting them. Snapping bars

should be spaced closer together inthe front (~11/4 inch) than at the rear(~13/8 inch) to avoid wedging. Keeptrash knives sharp and set them asclose to the rolls as possible to pre-vent wrapping the stalks and plug-ging the machine.

Operation of the cylinder/rotor af-fects corn kernel damage more thanany other machine setting, so atten-tion to this detail will yield large ben-efits during drying and storage. Grainmoisture also influences the amountof kernel damage and may vary withdifferent varieties, but fines generallyincrease at moisture levels above 25percent. Since large variations existamong current combine models, pro-ducers should closely follow theoperator’s manual for speed and clear-ance settings suggested for their cyl-inder or rotor machine. Avoidoverthreshing, which increases kerneldamage, produces excess fines, andconsumes more power and fuel.

Economic Incentive toReduce Harvest Losses

Many farmers are not aware of themagnitude of their harvest losses. Al-though they can vary widely from yearto year, studies have shown them tobe as high as 15 percent or more ofpotential yield. Perhaps the best mo-

Table 3. Dimensions of a 10-square-footarea for different row widths.

Row width (inches) 20 30 36

Row length (inches) 72 48 40

Table 4. Comparison of harvest losses at different yield levels and corn prices with dryingenergy costs.

Value of harvest losses ($/ac)Drying energy

cost2 ($/ac)

Loss level(% of yield)

Potentialyield

(bu/ac)

Harvestloss1

(bu/ac)

Corn prices ($ / bu) Moisture removed

$ 2.00 $ 2.50 $ 3.00 5 pts. 10 pts.

2% 100 1.97 $ 3.94 $ 4.93 $ 5.91 $ 7.72 $ 15.44

150 2.96 $ 5.91 $ 7.39 $ 8.87 $ 11.58 $ 23.16

200 3.94 $ 7.88 $ 9.85 $ 11.82 $ 15.44 $ 30.88

5% 100 4.93 $ 9.85 $ 12.31 $ 14.78 $ 7.48 $ 14.96

150 7.39 $ 14.78 $ 18.47 $ 22.16 $ 11.22 $ 22.44

200 9.85 $ 19.70 $ 24.63 $ 29.55 $ 14.96 $ 29.92

8% 100 7.88 $ 15.76 $ 19.70 $ 23.64 $ 7.24 $ 14.48

150 11.82 $ 23.64 $ 29.55 $ 35.46 $ 10.86 $ 21.72

200 15.76 $ 31.52 $ 39.40 $ 47.28 $ 14.48 $ 28.961 Harvest loss above an assumed minimum of 1.5% of potential yield.2 Drying energy cost based on a fuel price of $ 0.75 per gallon of LP or equivalent.

tivation for measuring harvest lossesis to consider the cost of grain left inthe field. These are shown in Table 4for various corn prices, potential yield,and harvest loss levels. Even with lowcorn prices, producers obviously needto keep losses below 5 percent regard-less of yield. Also, corn left in a fieldwill be a “weed” the following year andwill have to be controlled, resultingin a higher cost.

Drying ConsiderationsCorn drying equipment consists of

bin dryers, column dryers, or a com-bination of these two types. Each sys-tem uses different amounts of heat andairflow to achieve the desired capac-ity, control drying costs, and maintaingrain quality. Regardless of the typeused, high-moisture corn should bedried to 16 percent moisture within24 hours and cooled to the outside airtemperature within 48 hours afterharvest to avoid losses due to heat-ing, which can provide an ideal envi-ronment for mold activity and canlead to mycotoxin production. If heat-ing is prolonged, dry matter loss andan associated loss in quality and testweight will most certainly occur. Theamount of time that clean high-mois-ture corn can be held safely without aloss in quality varies with grain tem-

55

perature, as shown in Table 5. Thesetimes can be reduced by as much asone-half or more for broken corn witha high level of fines, trash, and for-eign material.

The amount of water in shelledcorn at various moisture levels isshown in Table 6. No. 2 yellow cornis usually marketed at 15.0 or 15.5 per-cent wet basis (w.b.), whereas food-grade corn is usually sold at 14.0percent w.b. All corn should be driedto 13.0 percent moisture if it will beheld into the summer, so the storagecosts for drying and moisture shrinkmust be recovered by market in-creases. Otherwise, corn should bedried to the market level, cooled assoon as possible in the fall, and soldbefore warm weather the followingspring rather than risk the chance ofspoilage because of mold and insectactivity.

Corn dryers range in capacity froma few hundred to several thousandbushels per day. Producers should sizetheir dryer(s) to match daily combinecapacity and harvest moisture targetlevels. Suggested operating condi-tions for different corn drying systemsin Kentucky are listed in Table 7.More information for each dryingsystem is available in other Exten-sion publications.

Because fan capacity diminishes asa bin is filled, full bin drying with un-heated or low temperature air takesseveral weeks to accomplish becauseof low airflow rates. Consequently,these slow processes are not recom-mended for corn above 18 percentmoisture. Also, the top layer of cornis the last to dry in bins without stir-ring augers, so this layer should bechecked frequently during drying toavoid environmental conditions thatfavor mold growth. If more drying ca-pacity is needed, first reduce the depthof corn to increase airflow, then addmore heat if possible. Other sugges-tions for increasing bin drying capac-ity are presented in the Extensionpublications listed in Table 7. Con-

Table 5. Allowable holding time for clean shelled corn at different temperature and moisturelevels before a loss in grade occurs.1

Graintemperature

Corn moisture content (% wet basis)

18% 20% 22% 24% 26% 28% 30%

Allowable holding time (days)

40˚F 195 85 54 38 28 24 20

50˚F 102 46 28 19 16 13 11

60˚F 63 26 16 10 8 6 5

70˚F 37 13 8 5 4 3 2

80˚F 27 10 6 4 3 2 11 A grade loss occurs when corn loses 0.5 pound of dry matter per bushel. Source: ASAE.

Table 6. Amount of water in shelled corn (test weight of 56 lb/bu) at different base moisturelevels.

Moisture content, % wetbasis

13 15 17 19 21 23 25 27 29

Water (15.0% base), lb/bu 7.1 8.4 9.8 11.2 12.7 14.2 15.9 17.6 19.4

Water (14.0% base), lb/bu 7.2 8.5 9.9 11.3 12.8 14.4 16.1 17.8 19.7

sider installing grain temperature andmoisture content sensors in new orexisting bin dryers to control fan andheater operation or unloading equip-ment cycles. Reducing labor andoverdried or underdried corn can of-ten quickly pay for automatedcontrols.

High temperature in-bin and col-umn dryers provide the most capac-ity and flexibility for drying corn athigh moisture levels. Drying times areusually between a half-hour and twohours. A potential trouble area withthese systems is the wet holding binwhere grain accumulates as it is de-livered from the field and awaits trans-fer to the dryer. When high-moisturecorn stays in a wet bin too long, moldgrowth can begin within 24 hours andaccelerate rapidly if left in the bin.

Aeration in wet holding bins pro-vides some temperature control for wetcorn, but it is not a substitute for timelydrying. Hopper bottom bins are pre-ferred for holding wet corn becausethey are self cleaning when unloadedcompletely. Consequently, it is a goodidea to empty hopper tanks completelyeach day during harvest to avoid thepossible accumulation of smallamounts of wet grain. If flat bottombins are used to hold wet corn, use apower sweep auger to unload the bin

completely each day or form a “false”hopper bottom with dry corn to facili-tate daily unloading of wet grain.

Dryeration or in-bin cooling of hot,dry corn is a popular way to increasedrying capacity, reduce drying costs,and reduce stress-cracked kernels, yetit can create some problems if corn isnot cooled within 48 hours after dry-ing. A minimum airflow rate of 0.5cubic feet per minute (cfm) should beprovided for each bushel of hot cornto achieve the desired cooling time.Also provide 1 square foot of roof ex-haust for every 1,000 cfm of fan capac-ity. When cooling hot corn in a bin,the fan should run continuously to re-move condensed moisture that accu-mulates on the roof and inside wall.

Storage ConsiderationsThe best way to protect dry stored

corn from spoilage by mold and in-sect activity is to apply integrated pestmanagement practices, which arebased on an understanding of theecology of grain pests. The applica-tion of a broad range of preventivepractices has a cumulative effect onpest control. Examples include clean-ing grain bins and the area surround-ing them prior to harvest, controllinggrain moisture throughout drying,cleaning dried corn prior to storage

56

Table 7. Comparison of corn drying systems for Kentucky conditions.

Dryer type

Relativedrying

capacity(bu/day)

Airflowrate

cfm/buAir

temp. oF

Harvestmoisturecontent

limit% wet basis

Relativeinitial cost

Grainquality Disadvantages

UKpublication

Bin dryers

No heat Low(150)

12

Outside air 16%18%

Low tomedium

Excellent Very limited capability athigh moisture levels

AEN-23

Lowtemperature

Low(150)

12

Outside+ 5 – 10

18%20%

Low tomedium

Excellent Limited capability at highmoisture levels

AEN-22

Layer fill Low(150)

25

Outside+ 20

22%24%

Low tomedium

Good Limited capability at highmoisture levels

AEN-56

Mediumtemperature

Medium(2,000)

8 - 12 120 – 140 28% Low tomedium

Good Requires level grain depth,batch transfer, labor, and

downtime

AEN-57

Hightemperature

High(6,000)

15 - 70 160 – 180 30% Medium Good Metering equipmentrequires maintenance

AEN-63

Column dryers

Recirculating High(6,000)

75 - 125 180 – 220 30% Medium Good High labor required toload/unload dryer

AEN-64

Automaticbatch

High(8,000)

75 - 125 180 – 240 30% High Fair Requires wet holding binand support handling

equipment

AEN-65

Continuous flow

High(10,000)

75 - 125 180 – 240 30% High Fair Requires wet holding bin,support handling

equipment, and controls

AEN-65

In-bin cooling away from dryers

Hightemperaturedryer withdryeration

High(10,000)

10 – 125&

½ - 1

120 – 240&

outside air

30%&

16%

Medium Excellent Requires extra grainhandling and managingmoisture condensation

AEN-23AEN-65

Hightemperaturedryer with in-bin cooling

High(10,000)

10 – 125&

½ - 1

120 – 240&

outside air

30%&

16%

Medium Good More management formoisture condensation and

cooling

AEN-22AEN-65

to remove broken kernels and trash,controlling temperature throughoutstorage, managing the depth of grainin the bin to permit uniform airflow,and monitoring grain during storagefor temperature, moisture, and moldand insect populations. By applyingall these practices, a post-harvest In-tegrated Pest Management (IPM)strategy can be substituted for someor all of the chemicals that have tra-ditionally been used to control pestsin stored grain.

Corn with a high level of trash andfine material that has been underdriedor not dried uniformly can developproblems during storage quickly eventhough the average moisture readingsthroughout the bin may be 15 per-cent. Thus, it is wise to check the toplayer of corn in all storage bins abouta week after drying and cooling to be

sure that no moisture buildup has oc-curred. If elevated temperatures ormoisture conditions are left un-checked, mold and insect growth canflourish even in cool weather becausetheir activity produces heat, whichaccelerates grain deterioration further.

Controlling the moisture contentand temperature of corn throughoutthe storage period is the most cost-effective way to prevent spoilage prob-lems and potential dockage frommusty odors, insects, low test weight,and poor condition. Table 8 shows therecommended storage conditions forclean corn throughout the year inKentucky. These are based on theequilibrium moisture content proper-ties of corn and the fact that mold andinsect activity is held in check whengrain temperatures are below 55°F andthe relative humidity in the air space

between corn kernels is below 65 per-cent (Table 9 and Figure 1). Cleancorn that is dried to 15 percent mois-ture, cooled in September to 65°F, andcooled an additional 10° to 15°F eachmonth during the fall should storewell for up to six months.

Stored corn can spoil if it is driedto the recommended moisture levelbut not cooled thoroughly. Unevengrain temperatures can lead to mois-ture migration (which usually occursin the top center of the bin), whichcan promote mold growth and insectactivity. Aeration equalizes grain tem-peratures throughout the bin and pre-vents moisture migration. The timerequired to aerate corn depends pri-marily on the size of the fan relativeto the amount of grain. Approximatetimes for different combinations of fanhorsepower and bin capacity are given

57

Table 8. Recommended grain temperature and moisturelevels during storage in Kentucky.1

MonthAverage air

temperatureTarget graintemperature

Target grainmoisturecontent

September 70˚ F 60˚ – 70˚ F 14.0 %

October 60˚ F 50˚ – 60˚ F 15.0 %

November 47˚ F 42˚ – 52˚ F 15.0 %

Dec – Feb 37˚ F 32˚ – 42˚ F 15.0 %

March 47˚ F 42˚ – 52˚ F 14.0 %

April 55˚ F 50˚ – 60˚ F 13.0 %1 Source: AEN-45, Aeration, Inspection, and Sampling of Grainin Storage.

Table 9. Equilibrium moisture content (% wet basis) for shelled yellow corn.1

Temperature Relative humidity (%)

˚C

2

4

10

16

21

27

32

38

F

35

40

50

60

70

80

90

100

10

6.5

6.2

5.7

5.3

4.9

4.6

4.2

3.9

20

8.6

8.3

7.8

7.3

6.9

6.5

6.1

5.8

30

10.3

9.9

9.4

8.9

8.4

8.0

7.7

7.3

40

11.8

11.5

10.9

10.3

9.9

9.4

9.1

8.7

50

13.3

12.9

12.3

11.8

11.3

10.8

10.5

10.1

60

14.8

14.5

13.8

13.3

12.8

12.3

11.9

11.5

65

15.7

15.3

14.7

14.1

13.6

13.1

12.7

12.3

70

16.6

16.2

15.5

15.0

14.4

14.0

13.5

13.1

80

18.7

18.3

17.6

17.0

16.4

16.0

15.5

15.1

90

21.7

21.3

20.5

19.9

19.4

18.8

18.4

17.91 Source: ASAE Data D245.4 (average of two prediction equations).

Table 10. Approximate operating times for different size fans (by horsepower).

Fan capacityhp/1000 bu

Hours of fanoperation

Operating mode whencooling hot corn1

Operating modewhen aerating1

1.0 15 – 20 C I

¾ 20 – 25 C I

½ 30 – 40 C I

¼ 60 – 80 NR C

1/5 75 – 100 NR C

1/10 150 – 200 NR C1 C = continuous fan operation for the time shown when the average air temperature is in thedesired range. I = intermittent fan operation when the air temperature is in the desired range.NR = not recommended.

Figure 1. Equilibrium moisture content (% w.b.) for shelled yellow corn forwinter and summer conditions.

0

24

Co

rn M

ois

ture

, %w

b

0 20 40 60 80 100

Relative Humidity, %

35˚F

80˚F

in Table 10. Times shown are requiredto move an aeration cycle completelythrough a bin. Two to three cycles arenormally required each fall to coolcorn from 70°F to 35°F in Kentucky.

Another good management prac-tice is to remove the top cone of cornthat occupies the upper portion of thebin. Many managers are reluctant todo this because they view this as a lossof storage capacity. However, mostcorn storage problems in overfilled binsbegin in the upper center of the grainmass because that area receives littleairflow since air follows the path ofleast resistance and bypasses the deep-est grain. While removing the top coneof corn, trash and fines that tend toaccumulate in the center of the bin arereduced, which lets air move throughthe center of the bin much more eas-ily. Corn from this area should be heldin a separate bin and fed to livestockor sold quickly since it has a relativelyhigh concentration of broken corn,trash, and fine material. The trade-offof removing the top cone of corn is im-proved airflow and adequate room forworkers to probe the bin and check forpossible problems.

Stored corn should be inspectedevery 1 to 2 weeks in the fall andspring and once every 2 to 4 weeksafter conditions in the bin have sta-bilized during the winter months. Allworkers should be made aware of thesuffocation and entrapment hazardsthat exist with flowing grain as well

as the personal safety risks associatedwith grain dust. A safe sampling pro-tocol is provided in more detail in Ex-tension publication Aeration, Inspection,and Sampling of Grain in Storage Bins(AEN-45).

A suggested list of equipmentneeded to inspect stored grain safelyis shown in Table 11. Corn samples

may be sealed in plastic bags andtaken to a farm shop or office for ob-servation. Kernel moisture, tempera-ture, and condition should berecorded during each inspection andcompared with previous samples.Samples should be sieved to look forinsects when corn temperatures riseabove 55°F. If conditions change to-

58

Table 11. Cost estimates for tools needed to collect andinspect corn samples from on-farm bins.

ToolRecommended/

OptionalApproximate

cost

Dust mask(s) R $ 1 - 500

Insect probe traps R $ 20

Portable moisture meter R $ 300

Dial thermometer R $ 10 - 55

Grain probe/trier R $ 80

Corn sieves R $ 70

Temperature/RHpsychrometer

R $ 60

Temperature readoutdevice

O $ 300 - 500

Temperature cables (per bin)

O $ 200 - 800

Aeration controller O $ 400 - 4,000

Total range $ 541 - 6,385

ward temperature or moisture levelsthat favor mold or insect activity (i.e.,elevated grain temperature or mois-ture), run aeration fans to cool thecorn thoroughly (see fan operatingtimes in Table 10 as a guideline). Ifconditions continue to worsen, trans-fer the grain to another bin and col-lect a sample every two to five minutesduring unloading. Redry moist cornto a safe level as quickly as possible orsell the lot to an elevator if drying isnot an option.

Diligent monitoring of stored graincan help producers avoid problemsthat too often go entirely unnoticed.The authors have seen cases wheregrain spoilage was so severe that at-tempts to unload corn from a storagebin were unsuccessful because dete-rioration had advanced to the pointwhere a large mass of grain was stucktogether and wouldn’t flow. Suchcases can be avoided entirely with

prudent management of stored corn.Hopefully, the reminders and recom-mended actions mentioned here willhelp producers and overseers of storedgrain maintain and market high qual-ity corn.

59

MarketingSteve Riggins

Acreage devoted to corn productionin Kentucky has been quite stable eversince farmers have had time to adjustto the new lower loan rates for cornthat came out of the 1985 Farm Bill.The government programs of the1970s and the 1980 law led to in-creases in corn acres both nationallyand in Kentucky (Figure 1). Theseprograms had built-in adjustments forhigher loan rates if costs of corn pro-duction increased. Very sharp in-creases in energy cost and increasesin interest rates produced higher loanrates and guaranteed minimum pricesfor farmers participating in the feed-grain government program. In con-trast, the soybean loan rate was frozen.

As stockpiles of corn grew and cornexports remained relatively flat in theUnited States, prices to farmers fellsharply, except during a few droughtyears when supply was reduced. The1985 farm law changed the way loanrates were determined, and the 1990and 1996 laws continued that ap-proach. The average corn loan rate inthe United States has been stable at$1.89 per bushel since 1994.

Yield-enhancing technology, how-ever, has continued to propel produc-tion ever higher, with national averagecorn yields improving about 1.7 bush-els per acre per year. Annual yield im-provement in Kentucky has just aboutmatched the national rate of increaseat 1.6 bushels per acre per year. It isalso apparent that Kentucky cornyields closely track national corn yieldsin most years. However, the years 1997,1998, and 1999 were evidence thatsometimes Kentucky corn yields don’tmirror what happens in the corn belt(Figure 2).

As acreage devoted to corn produc-tion has remained relatively flat andwhile yield has steadily improved, thenumber of farms that grow corn inKentucky has dropped significantlyover the past several years (Table 1).

It is also apparent from Table 1 thatfarms with small corn acreages aredropping out while the number of thelargest corn farms are increasing theirshare of total state corn production.

As the concentration of corn (andsoybean and wheat production) in-creases, so does the concentrationwithin the agribusiness sector servinggrain farms. According to the Direc-tory of the Kentucky Feed & Grain As-sociation of 1994, there were 194licensed grain dealers and warehouses,while the most recent listing indicatesthere are only 181 such entities. Ad-ditionally, the Kentucky Fertilizer &Agricultural Chemical Association Di-rectory of 1994 listed 143 differentfirms as members, while the 2001 di-rectory contains a listing for 120 dif-ferent firms.

790

1800

1600

1400

1200

1000

800

600

400

200

80

Tho

usa

nd

Acr

es

Year

81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 00

Figure 1. Kentucky harvested corn acreage.

19750

20

40

60

80

100

120

140

160

1980 1985

Bu

shel

s p

er A

cre

1990 1995 2000

U.S. YieldKentucky Yield

Figure 2. U.S. and Kentucky corn yields.

Data from the most recent issue ofKentucky Agricultural Statistics(1999-2000) also support the idea ofa mature corn industry in Kentuckythat is increasingly becoming moreconcentrated at both the farm and as-sociated agribusiness level. The num-ber of commercially operated off-farmgrain storage facilities has droppedfrom 224 in 1985 to 217 in 1999,while total storage capacity has essen-tially remained stable. In addition, on-farm rated grain storage capacity hasremained relatively unchanged at ap-proximately 180 million bushels(Table 2). It will be interesting to ob-serve what happens to grain storagecapacity with time under the more“market oriented” 1996 Farm Bill.The excellent weather and resultinglarge crops have created a very strong

60

Table 1. Number of corn farms in Kentucky by size 1987-1997.

1987 1992 1997

Corn for grain (all farms) 25,067 16,945 11,021

1-14 acres 13,147 7,293 4,060

15-24 acres 3,657 2,315 1,440

25-49 acres 3,642 2,692 1,615

50-99 acres 2,209 1,897 1,408

100-249 acres 1,555 1,599 1,390

250-499 acres 598 716 607

1,000 acres or more 48 109 157

Total number of all farms 92,453 90,281 82,273

Source: Census of Agriculture. Various issues.

Table 2. Kentucky off-farm and on-farm grain storage capacity:December 1, 1985-1999.

Off-farm storage On-farm storage

Number offacilities

Rated storagecapacity

(1,000 bu)

Rated storagecapacity

(1,000 bu)

1985 224 56,350 NA

1990 262 61,350 190,000

1994 238 57,500 180,000

1995 236 55,510 170,000

1996 233 57,820 190,000

1997 229 59,250 180,000

1998 218 58,870 180,000

1999 217 59,200 180,000

Source: Kentucky Ag Statistics 1999-2000.

“carry” in the market for grain stor-age. Casual observation indicates thatfarmers have responded in the past 18to 24 months by adding significantlyto on-farm storage capacity. Thisshould begin to show up in the Ken-tucky Agricultural Statistics reportsstarting with the 2000-2001 issue.

The mature corn and soybean/wheat industry and the increasingconcentration of grain productionimplies that competition for availableland base for grain production will bevery intense and result in very thinaverage operating margins over timefor grain farmers. In years of above-average yields, farmers should earnample profits, while in poor yieldingyears, it will be nearly impossible fornon-owned land to cash flow.

The skill or luck involved in thetiming of the pricing decision is onearea that could make a difference infarm survivability. Recent weekly cornprice data from the Green River areaof Kentucky serve to illustrate boththe within-season and season-to-sea-son price variability faced by Ken-tucky grain farmers. At first glance,the price pattern for the past threecrop season looks remarkedly similar.However, the September/early Octo-ber 2000 price was some 15 to 20 centsper bushel less than the price from thesame time period for the 1998 and1999 crops. At the 2000 Kentuckycorn average yield of 130 bushels peracre, that difference represents $20 to

$25 per acre, a substantial sum for atypical Kentucky large grain farm. Thewithin-season price range for the2000-crop corn marketing year in thisarea ranged from just under $1.60 perbushel at harvest to more than $2.30per bushel in late December, and backdown to $2.00 in late March 2001(Figure 3). With perfect hindsight, itis clear that cash receipts per acrecould have varied as much as $90 (70cents/bu x 130 bu yield). This is on afarm with average state yields for thatcrop year. Clearly farmers stand tobenefit from improving both theirproduction skills as well as their mar-keting skills.

In an attempt to better understandcurrent pricing and marketing prac-tices of large Kentucky grain farms,survey data were collected from anon-random sample of Western Ken-tucky grain producers. The full de-tails of this research are contained in

“Pricing Practices of Selected West-ern Kentucky Grain Farms,” Agricul-tural Economics Extension No.2000-12, published by the Universityof Kentucky Cooperative ExtensionService in May 2000. The followingsections of this paper draw heavilyon that report.

Usable data were obtained from130 farms in 11 counties in WesternKentucky. The average farm in thesurvey cropped 624 acres of corn, 617acres of soybean, and 211 acres ofwheat. In addition, these farms aver-aged slightly more than 55,000 bush-els of grain storage capacity, frequentlyan important component of a grainmarketing plan. Based on averagestate yields for corn, soybean, andwheat, the average sample farm of1,452 acres controlled sufficient grainstorage capacity to cover about halfof their expected total grain and soy-bean production.

140

160

180

200

220

240

Pri

ce

Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul

1998-99

1999-2000

2000-2001

Figure 3. Cash corn prices—Green River area.

61

Table 3. Farmers’ marketing methods: Corn.

Farmersusing thistechnique

% offarmers

reportedusing thistechnique

Average %of crop

marketedby this

method

1. Cash out-of-field COF 80 61.5 16.8

2. Cash out-of-bins COB 84 64.6 28.2

3. Elevator cash-forward contracts El.FC 77 59.2 26.3

4. Elevator basis contracts El.BC 24 18.5 4.1

5. Elevator delayed price (DP) contracts El.DPC 43 33.1 10.3

6. Elevator hedge-to-arrive contracts El.HTA 19 14.6 3.4

7. Elevator min price contract El.MPC 2 1.5 0.1

8. Futures markets plus cash sales FH+Cash 7 5.4 1.6

9. Futures markets plus elevator contractsFH+El.C 8 6.2 0.0

10. Futures options plus cash sales FO+Cash 6 4.6 0.7

11. Futures options plus elevator contracts FO+ElC 7 5.4 1.4

Pricing MethodsThe specific aim of this research

project was to discover the method(s)and time frame most often employedby grain producers to price and mar-ket their crop production. Farmerswere asked to indicate the percentageof each crop (corn, soybean, wheat)they had priced via 11 different tech-niques over the 1995 through 1997crop marketing seasons (Table 3). Theywere instructed to account for 100 per-cent of each crop each season. The 11marketing methods and a short descrip-tion, if necessary, follows:1. Cash out-of-field—no explana-

tion necessary.2. Cash out-of-bins—farmer owns

bins or elevator storage program;grain still owned by farmer.

3. Elevator cash- forward contract—traditional cash contract for fu-ture delivery.

4. Elevator basis contract—quan-tity/delivery date specified in ad-vance of delivery; basis negotiatedon initial contract date; title trans-fers to elevator at delivery; farmermay or may not receive any cashat delivery; final pricing could bebefore or after delivery, typicallyat or after delivery; final pricingmust occur by definite date, orfarmer must negotiate new end-ing date and pay additional fees.

5. Elevator delayed price (DP) con-tract—farmer delivers grain; mayor may not receive any cash atdelivery; title transfers to the el-evator; farmer must set final cashprice by set date or pay fees to“roll” the contract to a later date.

6. Elevator hedge-to-arrive (HTA)contract—specific futures con-tract month and price and a spe-cific quantity negotiated prior todelivery; basis typically negoti-ated at or prior to delivery.

7. Elevator minimum price con-tract—minimum price; quantityand delivery date set on initialcontract date; elevator typicallyshorts the appropriate futures con-tract month and buys an appro-

priate call option strike price anddelivery month; they charge thefarmer all costs plus an additionalservice fee; final total net farmprice is established on deliverydate.

8. Futures market plus cash sale—cash sales could be from field orbin; futures transaction could be ashort hedge coupled with a latercash sale, or it could be the pur-chase of a long futures position asa replacement for a cash sale.

9. Futures market plus cash forwardcontract sale—offset short hedgeand replace with cash contract oradd a long futures position to anexisting cash forward contract.

10. Futures options plus cash sales—cash sales could be from the fieldor bin; could buy a put first andsell cash grain later; could sellcash grain first and replace withthe purchase of a call option.

11. Futures options plus elevator con-tracts—could be the purchase of acall option combined with an el-evator cash forward contract;could also be offsetting a put op-tion and converting to a cash for-ward contract.

Clearly, the 11 pricing methods donot cover all possible convolutions ofmarketing methods that could be de-vised or offered by the marketplace.However, the authors believe the

above list of methods account for es-sentially all pricing methods currentlyin use in Kentucky. Additionally, itshould be noted that methods eightthrough 11 could involve some slightvariations beyond those listed in theabove explanation. The goal of thesurvey instrument was to measure thedegree of use of futures and futures op-tions market in a general sense, not asan exact measurement of each possiblevariation of use of these methods.

Nearly two-thirds of the respon-dents in the survey reported usingcash out-of-bins as a marketingmethod for corn (Table 3). This wasclosely followed by cash-out-of-fieldand elevator cash forward contractsas the methods used by most farmersin the sample data. A sizeable percent-age of farmers, 18.5 percent, also usedDP contracts, while 14.6 percent offarmers in the sample also used HTAcontracts. The number of farmers inthe sample who reported using futuresor options as marketing methods dur-ing the 1995-1997 crop marketingyears was very modest, ranging from4.6 percent to only 6.2 percent.

When asked to identify the percentof their corn crop marketed by eachmethod, farmers showed the strongestpreferences for cash-out-of-bins andcash-forward contracts as the twodominant marketing methods. Thesetwo methods accounted for nearly 55percent of all sales during the three-

62

Table 5. Timing of pricing decisions: Corn.

Totalresponses

pereach

% of farmersreportedusing thistechnique

Average %marketed

at thistime Code

More than a month beforeplanting

68 52.3 13.9 BePlnt

During planting season 35 26.9 5.4 @Plnt

Planting until mid-season 47 36.2 7.8 Plnt-Mid

Mid-season until crop maturity 55 42.3 10.3 Mid-Mat

During harvest season 56 43.1 12.7 @Harv

During month after harvest 35 26.9 7.6 AftHar

More than a month afterharvest

94 72.3 39.1 >1moAftHar

Timing of Grain SalesTiming of grain sales is a question

of interest in understanding farmers’marketing habits. The survey formbroke the marketing year into seventime periods (Table 5) and asked farm-ers to indicate the percentage of eachcrop priced during each period.Clearly, the period identified as morethan a month after harvest is the mostused time period for pricing corn. Thesecond major pricing period is theperiod labeled as more than a monthbefore planting. Together these twotime periods account for 53 percentof annual corn pricing decisions. It isalso clear there could be some over-lap between these two ill-defined timeperiods. These results are consistentwith the earlier data for corn that in-dicate a heavy reliance on cash-out-of-bins, cash-forward contracts, andDP contracts as significant pricingmethods and the corn data on con-tract delivery periods that indicate theJanuary-February and March-Maytime periods as the two major periodsof contract delivery. The data are alsoconsistent with the harvest seasonbeing the third most important pric-ing period and cash-out-of-field beingthe third most used pricing method.

Information obtained from the sur-vey results concerning farmers’ use offutures options was somewhat consis-tent. Farmers were asked how manytotal times over the past three mar-keting years they had used options toset price floors prior to any active pric-ing on the cash side and how manytimes they had used options to par-

year period examined by the survey in-strument. Cash-out-of-field (16.8 per-cent) accounted for the third largestpercentage of corn marketings amongfarmers in the survey. DP contracts, atslightly more than 10 percent, was theonly other method with double digituse by farmers marketing corn. The topfour marketing methods (two cashstrategies and two elevator contracts)represented more than 81 percent ofall corn sales by survey respondents. Incontrast, the four methods involvingthe use of futures and options marketsaccounted for less than 6 percent oftotal marketings. Even though farm-ers were instructed to account for allsales, some did not do so; therefore,total sales from all methods only addsto 95 percent.

Contract Delivery PeriodsFarmers make extensive use of el-

evator contracts as a method of mar-keting corn, soybean, and wheat. The130 farmers represented in this samplepriced 26 percent, 24 percent, and 26percent, respectively, of their corn,soybean, and wheat with cash-forwardcontracts. Additionally, other types ofelevator contracts accounted for 18percent of corn sales, 32 percent ofsoybean sales, and 12 percent of wheatsales. The primary delivery period forcontracted corn was January-February,followed by the “Fall” period whileMarch-May was the third most con-tracted delivery time period (Table 4).Farmers were supposed to account for100 percent of all contracted grain;however, some failed to do so, leav-ing nearly 16 percent of all contractsales unaccounted for from a deliverytime perspective.

ticipate in a futures market rally afterthey had priced the cash grain. Theywere also asked to list the total num-ber of puts and calls (by crop) theyhad purchased over the same time pe-riod (Table 6). As an example, cornfarmers had used options to set pricefloors 142 times, and they claimed tohave purchased 134 puts, “reasonablyclose.” They also claimed to have usedoptions 97 times to participate in afutures market rally after they hadpriced cash corn and they purchased109 calls.

Only nine of the 130 farmersclaimed to have speculated in theoptions market over the time periodsurveyed. Essentially all of this activ-ity was focused on corn, with 35 putssold and 25 calls sold. There werethree soybean puts sold and four soy-bean calls sold. For wheat, only twocall contracts were sold as speculativepositions, while no puts were sold.

Factors InfluencingPricing Decisions

Survey respondents were asked torank, from 1 to 10 (with 10 being themost important), their sources of in-formation and contingent factors thatinfluenced the pricing decisions fortheir crops. Satellite market informa-tion systems were the top choiceamong the 10 provided on the surveyform (Table 7). Marketing newslettersand private consultants also rankedhigh in the farmer survey. Neighbors,bankers, and cash flow needs/require-ments were less well regarded as aidsin making crop pricing decisions.

Table 4. Periods of contract delivery: Corn.

Average % of crop contracted for

deliveryduring specified period

June-July 2.0

Aug-Sept 6.5

"Fall" 25.2

Jan-Feb 38.1

Mar-May 12.5

63

ConclusionsThe farmers who participated in

this non-random sample farm muchlarger acreages than are common fornon-grain farms in Kentucky. Thesefarmers also own or control sufficienton-farm storage to handle about halfof their expected annual grain produc-tion. This group of farmers reliesheavily on the latest communicationtechnology and paid professionals formarketing advice and assistance.While the group as a whole does not

Table 6. Direct use of futures and options markets by farmers.

Corn Soybean Wheat

Short hedge: Contracts 407 220 143

Farmers whospeculated

17 16 8

Option use: Before pricing 142 67 37

After pricing 97 94 67

Options bought: Puts bought 134 51 42

Calls bought 109 72 89

Farmers who soldoptions (all grains)

9

Options sold: Puts sold 35 3 0

Calls sold 25 4 2

Table 7. Farmers’ sources of marketingdecision information: All grains.

Rank1

Grain dealer 7 G.D.

Private market consultant

8 P.MktC.

Commodities broker 4 CmBro.

University resource 6 U.K.

Banker/Lender 2 Bank

Marketing newsletter 9 Mktlet.

Satellite market info. system

10 S.Mktinfo

Mass media 5 MassM

Neighbor 1 N. Farm

Cash flow 3 Cash Fl1 Rank over the survey population (10 =most important source or factor).

make heavy use of futures or optionsmarkets to price grain directly, theyalso sell less than 17 percent of theircorn and less than 15 percent of theirsoybean directly out of the field at har-vest. These farmers make significantuse of on-farm storage to contract formid-to-late winter delivery, they con-tract in late winter and early springfor harvest and fall delivery, and theyalso store sizeable quantities unpricedto sell after harvest.

This survey did not address thequestion of whether farmers are do-ing a good job of marketing. That is avery complicated question to answer.Clearly, these farmers are activelyseeking marketing advice, and theyare trying to spread sales throughoutthe marketing year. They are also em-ploying a wide array of marketingmethods. These are all signs of strongmarketing skills. It is possible that in-creased use of futures and optionsmarkets by farmers could be benefi-cial, but that is a testable hypothesis,not a fact.

64

Ayres, G.E. 1973. Profitable corn harvesting. Iowa StateUniversity. PM-574.

Brown, W.L., M.S. Zuber, L.L. Darrah, and D.V. Glover.1984. Origin, adaptation, and types of corn. NCH-10.

Byg, D.M. 1971. A guide for measuring corn harvest losses.The Ohio State University. AED-108.

Corn Production Handbook, 1994. Kansas State University.C-560 revised.

Egli, D.B., Doyle Cook, Allen B. Elam, and C.G. Poneleit.1971. Growing degree days for corn in Kentucky. KentuckyAgricultural Experiment Station. Progress Report 197.

Harner, J.P., and R.A. Higgins. 1994. Drying and storing. In:Corn Production Handbook. Kansas State University. C-560.

Hoeft, Robert G., Emerson D. Nafziger, Richard R. Johnson,and Samuel R. Aldrich. Nov. 2000. MCSP Publications,Champaign, Ill.

Johnson, R.R., D.R. Hicks, and D.L. Wright. 1985. Guide-lines for making corn replanting decisions. NCH-30.

Loewer, O.J., T.C. Bridges, G.M. White, and R.B. Razor.1982. Energy expenditures for drying and harvesting lossesas influenced by harvesting capacity and weather. Ameri-can Society of Agricultural Engineers. Paper No. 82-3515.

Midwest Plan Service. 1987. Grain drying, handling, andstorage handbook. MWPS-13.

McNeill, S.G. 2000. When should you start harvesting corn in2000? University of Kentucky Agricultural Economics De-partment. Economic and Policy Update. Vol. 00, No. 13.

Ritchie, Steven W., John J. Hanway, and Garren O. Benson.June 1993. How a corn plant develops. Iowa State Univer-sity of Science and Technology, Cooperative ExtensionService, Ames, Iowa. Special Report No. 48.

Traylor, R.K. 1994. Harvesting suggestions. In: Corn Produc-tion Handbook. Kansas State University. C-560.

Vorst, James V. 1991. Assessing hail damage to corn. NCH-1.

University of Kentucky Fact SheetsAEN-45 ............... Aeration, inspection, and sampling of grain

in storage bins.ID-59 ................... Aflatoxins in corn.ENTFACT 108 ... Armyworms in corn.AEN-57 ............... Batch-in-bin grain drying.BREI-2 ................. Biotechnology and the environment.ENTFACT 118 ... Bt corn.ENTFACT 128 ... Bt-corn refuges.ENTFACT 130 ... Bt corn: What it is and how it works.ENTFACT 100 ... Common stalk borer.ENTFACT 125 ... Corn leaf aphid.PPA-26 ................ Corn stalk rots.ENTFACT 59 ..... Cutworm management in corn.PPFS-AG-C-1 ..... Diseases of concern in continuous corn.

References

PPA-43 ................ Ear rot of corn caused by Stenocarpella.ENTFACT 49 ..... European corn borer management in corn.ENTFACT 110 ... Fall armyworm.PPA-35 ................ Gray leaf spot of corn.AEN-63 ............... In-bin continuous drying, method, and man-

agement.ENTFACT 16 ..... Insecticide recommendations for corn.IPM-2 ................... Kentucky integrated crop management

manual for field crops.ENTFACT 129 ... Lesser cornstalk borer.AGR-1 ................. Lime and fertilizer recommendations.AEN-22 ............... Low temperature drying: Methods and man-

agement.AEN-23 ............... Low temperature drying: Use and limita-

tions.ID-121 ................. Mycotoxins in corn produced by fusarium

fungi.IP-9 ...................... Pesticide residues in grains, vegetables, fruits,

and nuts.AEN-61 ............... Portable batch and continuous flow drying

method and management.AEN-20 ............... Principles of grain storage.ENTFACT 140 ... Resistance management with Bt corn.ENTFACT 309 ... Seedcorn maggots.PPA-33 ................ Stewart’s wilt of corn.ENTFACT 305 ... Stink bug damage to corn.AEN-62 ............... Stirring devices for grain drying.AEN-39 ............... Suffocation hazards in grain bins.PPA-40 ................ Virus diseases of corn in Kentucky.AGR-6 ................. Weed control recommendations for Kentucky

farm crops.ENTFACT 120 ... Wireworms in corn.

Web Pageshttp://lancaster.unl.edu/ag/crops/storage.htmhttp://pasture.ecn.purdue.edu/~grainlab/http://www.aces.uiuc.edu/value/factsheets/corn.htmhttp://www.ag.ohio-state.edu/%7Ehocorn/http://www.agen.ufl.edu/granary.htmlhttp://wwwagwx.ca.uky.edu/cgibin/cropdd_www.plhttp://www.bae.uky.eduhttp://www.bae.umn.edu/extens/postharvest/http://www.ca.uky.edu/agcollege/agcom/pubs/research/

respubs.htmhttp://www.ca.uky.edu/agcollege/plantpathology/

PPAExten/pppublin.htm#Corn and Sorghumhttp://www.exnet.iastate.edu/Pages/grain/http://www.uky.edu/Agriculture/Agronomy/files/agron.htmhttp://www.uky.edu/Agriculture/IPM/ipm.htmhttp://www.uky.edu/Agriculture/Entomology/enthp.htmhttp://www.usda.gov/gipsa/