Book Weed Management

7/28/2019 Book Weed Management

1/15

ATTRA is the national sustainable agriculture information service operated by the National Centerfor Appropriate Technology under a grant from the Rural Business-Cooperative Service, U.S.

Department of Agriculture. These organizations do not recommend or endorse products,companies, or individuals. ATTRA is headquartered in Fayetteville, Arkansas (P.O. Box 3657,

Fayetteville, AR 72702), with offices in Butte, Montana, and Davis, California.

PRINCIPLES OFPRINCIPLES OFPRINCIPLES OFPRINCIPLES OFPRINCIPLES OF

SUSSU SSUSSU SSUS TTTTTA INA INA INA INA INABLE WEEDABLE WEEDABLE WEEDABLE WEEDABLE WEED

MA NMA NMA NMA NMA NAAAAAGEMENT FGEMENT FGEMENT FGEMENT FGEMENT F OR CROR CROR CROR CROR CR OP LOP LOP LOP LOP LANDSANDSANDSANDSANDS

By Preston Sullivan

NCAT Agriculture Specialist

September 2003

AGRONOMY SYSTEMSSERIES

Abstract:To some extent, weeds are a result of crop production, but to a larger extent they are a consequence ofmanagement decisions. Managing croplands according to natures principles will reduce weed problems. And whilethese principles apply to most crops, this publication focuses on agronomic crops such as corn, soybeans, milo, andsmall grains. The opportunities to address the root causes of weeds are not always readily apparent, and often requiresome imagination to recognize. Creativity is key to taking advantage of these opportunities and devising sustainablecropping systems that prevent weed problems, rather than using quick-fix approaches. Annual monoculture crop

production generally involves tillage that creates conditions hospitable to many weeds. This publication discussesseveral alternatives to conventional tillage systems, including allelopathy, intercropping, crop rotations, and a weed-

free cropping design. A Resourceslist provides sources of further information.

First, Free Your Brain

As Iowa farmer Tom Frantzen poetically states:Free your brain and your behind will follow.What Tom is referring to is discovering new para-digms. Joel Barker, author of ParadigmsTheBusiness of Discovering the Future (1), defines a

paradigm as a set of standards that establish the

boundaries within which we operate and therules for success within those boundaries.

The weed controlparadigm is reactiveit addresses weedproblems by usingvarious tools and tech-nologies. How am Igonnaget rid ofthis vel-vet-leaf? and How doI control foxtail? are re-

active statements. Theconventional tools toget rid of or controlweedscultivation andherbicidesare reactivemeasures for solving the problem.

Farmers would generally agree that weeds arenot in the field because of a deficiency of her-bicides or cultivation. Rather, weeds are thenatural result of defying natures preferencefor high species diversity and covered ground.

Nature is trying to move the system in onedirection, the farmer in another. We createweed problems through conventional cropproduction methods. After we create theseproblems, we spend huge sums of money andlabor trying to control them.

TTTTTaaaaabbbbble ofle ofle ofle ofle of ContentsContentsContentsContentsContents

The Successful Weed.................................. 2

The Root Cause of Weeds ........................... 2Weed Seed Banks and Germination............. 3Proactive Weed Management ..................... 4Weed-Free by Design .................................. 7Reactive Measures ..................................... 8Weed Control Tools and Their Effects .......... 8Integrated Weed Management .................. 11Other ATTRA Publications of Interest ........ 12References ............................................... 12Additional Resources ...............................14
mailto:[email protected]?Subject=Sustainable%20Weed%20Managementmailto:[email protected]?Subject=Sustainable%20Weed%20Management


2/15PAGE 2 //PRINCIPLESOF WEED MANAGEMENT

The opposite of reacive thinking is proactivethinking, by which we seek what we wantthrough effective design and planning. A pro-active approach to weed management asks,Why do I have weeds? This publication willexpose you to some proactive principles of crop-land management that can make weeds less ofa problem. It also offers some reactive strate-

gies to deal with the weeds that remain bother-some.

The Successful Weed

Weeds can be divided into two broad catego-riesannuals and perennials. Annual weedsare plants that produce a seed crop in one year,then die. They are well adapted to succeed inhighly unstable and unpredictable environmentsbrought about by frequent tillage, drought, orother disturbance. They put much of their life

cycle into making seed for the next generation.This survival strategy serves plants in disturbedenvironments well, since their environment islikely to be disturbed again. The annual plantmust make a crop of seed as soon as possiblebefore the next disturbance comes. Annualplants also yield more seed than do perennialplants, which is why humans prefer annualover perennial crops for grain production.When we establish annual crop plants using till-age (i.e., disturbance) we also create an envi-ronment desirable for annual weeds.

Perennial weeds prosper in less-disturbed andmore stable environments. They are more com-mon under no-till cropping systems. Their ob-jective is to put some energy into preserving theparent plant while producing a modest amountof seed for future generations. After a field is

converted from conventional tillage to no-till,the weed population generally shifts from an-nual to perennial weeds. Perennial weeds pos-sess many of the characteristics of annualweeds: competitiveness, seed dormancy, andlong-lived seed. In addition to these character-istics, many perennial weeds possess perennat-ing parts such as stolons, bulbs, tubers, and rhi-

zomes. These parts allow the parent plant toregenerate if damaged and to produce newplants from the parent plant without seed.Additionally, the perennating parts serve asfood storage units that also enhance survival.These stored-food reserves allow for the rapidregrowth perennial weeds are known for.

The Root Cause of Weeds

When a piece of land is left fallow, it is sooncovered over by annual weeds. If the field is

left undisturbed for a second year, briars andbrush start to grow. As the fallow period con-tinues, the weed community shifts increasinglytoward perennial vegetation. By the fifth year,the field will host large numbers of young treesin a forest region, or perennial grasses in a prai-rie region. This natural progression of differentplant and animal species over time is a cycleknown as succession. This weed invasion, in allits stages, can be viewed as natures means ofrestoring stability by protecting bare soils andincreasing biodiversity.

Weeds are evidence of nature struggling to bringabout ecological succession. When we clearnative vegetation and establish annual crops,we are holding back natural plant succession,at great cost in weed control. To better under-stand this process, think of succession as a coilspring. Managing cropland as an annual mo-noculture compresses the springleaving itstraining to release its energy as a groundcoverof weeds. In contrast, a biodiverse perennial

grassland or forest is like the coil spring in itsuncompressed conditiona state of relative sta-bility with little energy for drastic change (Fig-ure 1) (2). Generally speaking, biodiversity leadsto more stability for the ecosystem as a whole.

Modern crop agriculture is typified by large acre-ages of a single plant type, accompanied by ahigh percentage of bare groundthe ideal en-vironment for annual weeds to prosper in the


3/15PAGE 3//PRINCIPLESOF WEED MANAGEMENT

Weed seed distribution and density in agricul-tural soils are influenced by cropping history andthe management of adjacent landscapes, andmay be highly variable. A study of westernNebraska cropland found 140 seeds per poundof surface soil, equivalent to 200 million seedsper acre (3). Redroot pigweed and commonlambsquarter accounted for 86%. Growing

without competition from other plants, a singleredroot pigweed plant can produce more than100,000 seeds, while a common lambsquarterplant can produce more than 70,000 seeds (4).

New weed species can enter fields by manyroutes. Equipment moved from one field to thenextespecially harvest equipmentspreadsweed seeds, as does hay brought from one farmto another. Crop seed is often contaminatedwith weed seed, and livestock transport weed

seeds from one farm to another in their diges-tive tracts and in their hair. Practical actionsthat can be taken to prevent the introductionand spread of weeds include the use of cleanseed (check the seed tag for weed-seed levels),cleaning equipment before moving from onefield to the next, and composting manures thatcontain weed seeds before applying them to thefield.

Survival and germination of weed seeds in thesoil depend on the weed species, depth of seed

burial, soil type, and tillage. Seeds at or nearthe soil surface can easily be eaten by insects,rodents, or birds. Also, they may rot or germi-nate. Buried seeds are more protected from seed-eating animals and buffered from extremes oftemperature and moisture. On average, about4% of broadleaf and 9% of grass weed seedspresent in the soil germinate in a given year (5).

Results from seed burial experiments demon-strated that seeds of barnyard grass and greenfoxtail buried at 10 inches showed germinationrates of 34 to 38% when dug up and spread onthe soil surface. In the same study, seed buriedat one inch showed only one to five percent ger-mination. In another study, seeds were buriedat different depths for a period of three years.Seed germination was greater with increasingdepth of burial (3). These studies show thatseeds near the surface face lots of hazards totheir survival, while those buried deeply by till-age are more protected. When those deep-bur-



ied seed are plowed up to the surface again theyhave a good chance of germinating andgrowing.

Table 1 shows that viable weed seeds are widelydistributed in moldboard and ridge-till systems.A higher percentage of seed remains near thesoil surface under chisel plow and no-till. The

moldboard plow and ridge-till systems are stir-ring the soil more, burying lots of weed seeds,and keeping weed seed more evenly distributeddown to a six-inch depth.

After a seed is shed from the parent plant, itcan remain dormant or germinate. There areseveral different types of dormancy. Seeds withhard seed coats possess innate dormancy.Several weed species, including pigweed, haveseed coats that require mechanical or chemicalinjury and high-temperature drying to breakdormancy. Another type of innate dormancy

can best be described as after-ripening, mean-ing the seed requires further development afterit falls off the plant before it will germinate.Several grass and mustard family weeds requireafter-ripening (7). Induced dormancy resultswhen seeds are exposed to unfavorable condi-tions, such as high temperatures, after beingshed from the parent plant. Enforced dor-mancy occurs when conditions favorable toweed germination are absent. The seeds remaindormant until favorable conditions return. Al-together, multiple types of dormancy ensure that

some weed seeds will germinate and some willremain dormant for later seasons.

Some weed species are dependent on light forgermination; some germinate in either light ordarkness; others germinate only in the dark.Thus, there are no hard and fast rules for man-aging an overall weed population according tolight sensitivity.

Manure application may stimulate weed ger-mination and growth. Studies have shown thatpoultry manure does not contain viable weedseeds, yet weed levels often increase rapidly inpastures following poultry manure application.Since chickens and turkeys have a gizzard ca-pable of grinding seeds, weed seeds are not likelyto pass through their digestive systems intact.

Additionally, most poultry rations contain fewif any weed seeds. The weed germination isprobably caused by effects of ammonia on theweed-seed bank already present in the soil. Theeffect varies depending on the source of the lit-

ter and the weed species present. Manurefrom hoofed livestock (e.g., sheep, cattle, andhorses), on the other hand, may indeed con-tain weed seed that has passed through theirdigestive systems. Composted manure con-tains far fewer weed seeds than does raw ma-

nure because the heat generated during thecomposting process kills them.

Fertilization practices can also affect weed ger-mination. Where fertilizer is broadcast, the en-tire weed community is fertilized along with thecrop. Where fertilizer is banded in the row, onlythe crop gets fertilized.

Proactive Weed Management Strategies

In the preceding sections, we saw how weeds

are established and maintained by human ac-tivities. So, how do we begin to manage anunnatural system to our best benefit withoutcompromising the soil and water? We can startby putting the principles of ecology to work onour behalf, while minimizing actions that onlyaddress symptoms.

Crops that ki l l w eeds

Some crops are especially useful because theyhave the ability to suppress other plants that

attempt to grow around them. Allelopathy re-fers to a plants ability to chemically inhibit thegrowth of other plants. Rye is one of the mostuseful allelopathic cover crops because it is win-ter-hardy and can be grown almost anywhere.Rye residue contains generous amounts of al-lelopathic chemicals. When left undisturbed onthe soil surface, these chemicals leach out andprevent germination of small-seeded weeds.Weed suppression is effective for about 30 to 60



days (8). If the rye is tilled into the soil, the ef-fect is lost.

Table 2shows the effects of several cereal covercrops on weed production. Note that tillagealone, in the absence of any cover crop, morethan doubled the number of weeds.

A weed scientist in Michigan (9) observed thatsome large-seeded food crops planted into ryemulch had high tolerance to the allelopathiceffects, while smaller-seeded crops had less tol-erance. In the study, corn, cucumber, pea, andsnapbean no-till planted under rye mulch ger-minated and grew as well or better than thesame crops planted no-till without mulch.Smaller-seeded crops, including cabbage andlettuce, showed much less germination, growth,

and yield. Weeds that were reduced by ryemulch included ragweed (by 43%), pigweed(95%), and common purslane (100%).

Dr. Doug Worsham, a North Carolina weedscientist, concluded that leaving a small grainmulch and not tilling gives 75 to 80% early-sea-son reduction of broadleaf weeds (10). Table 3shows the results of tillage, mulch, and herbi-

cides on weed control in a tobacco study (11).Just the absence of tillage alone gave 68% grasscontrol and 71% broadleaf control.

In other studies, North Carolina researchers in-vestigated combinations of herbicide use andcover crop plantings on weed control (12). Ryeand subterranean clover showed the highest

weed control without herbicides (Table 4). Nei-ther provided as much control as herbicides,however. Tillage reduced weed control consid-erably where no herbicide was used, as com-pared to no-tillage.

By seasons end the weed control resulting fromcover crops alone had decreased (Table 5). The

researchers concluded that additional weedcontrol measures must be applied with covercrops to assure effective weed control and prof-itable yields.

Other crops that have shown allelopathic effectsinclude sunflowers, sorghum, and rapeseed.Weed control ability varies among varieties andmanagement practices. Sweet potatoes havebeen shown to inhibit the growth of yellow nut-



sedge, velvetleaf, and pigweed. Field trialsshowed a 90% reduction of yellow nutsedgeover two years following sweet potatoes (13).

Rapeseed, a type of mustard, has been used tocontrol weeds in potatoes and corn under ex-perimental conditions. All members of the mus-tard family (Brassicaceae)contain mustard oils

that inhibit plant growth and seed germination(14). The concentration of allelopathic mustardoils varies with species and variety of mustard.

Researchers have begun to study ways to man-age mustards weed-suppressive abilities in cropproduction. In a Pacific Northwest study, fall-planted Jupiter rapeseed and sundangrasswere evaluated for suppression of weeds grow-ing in spring-planted potatoes. In the spring,the researchers either tilled or strip-killed therapeseed in preparation for potato planting. Thefirst year of the study, rapeseed reduced mid-season weed production 85% more than fallow-ing. By the end of the season, weed productionwas reduced by 98% with rapeseed, but only50% the second year. Potato yields are shownin Table 6.

In general, typical levels of cover crop residues,when left on the soil surface, can be expected toreduce weed emergence by 75 to 90% (15). Asthese residues decompose, the weed suppressioneffect will decline also. Residues that are morelayered and more compressed will be more sup-

pressive (15). Small-seeded weeds that havelight requirements for sprouting are most sensi-tive to cover crop residue. Larger-seeded an-nual and perennial weeds are least sensitive toresidue. Effective management strategies in-clude growing cover crops that produce highamounts of residue, growing slower-decompos-ing cover crops, packing the mulch down withimplements that compress it, and using meth-ods other than cover crops to control large-seeded annual and perennial weeds.

Smother Crops and Mulch

Certain crops can be used to smother weeds.Short-duration plantings of buckwheat and sor-ghum-sudangrass, for example, smother weedsby growing faster and out-competing them. Innorthern states, oats are commonly planted asa nurse crop for alfalfa, clover, and legume-

grass mixturesthe oats simply take the placeof weeds that would otherwise grow betweenthe young alfalfa plants.

With enough mulch, weed numbers can begreatly reduced. Nebraska scientists appliedwheat straw in early spring to a field wherewheat had been harvested the previous August.At the higher straw rates, weed levels were re-duced by more than two thirds (see Figure 2).Wheat, like rye, is also known to possess allelo-pathic qualities, which may have contributedto the weed suppression.

Figure 2: Weed Levels at two

Nebraska Locations (16).

0

100

200

300

400

500

600

0 0.75 1.5 2.25 3

Mulch rate - tons/acre

Weednumbers/acre

Sidney

North Platte

Crop Rotations

Crop rotations limit the buildup of weed popu-lations and prevent major weed species shifts.Weeds tend to prosper in crops that have re-quirements similar to the weeds. Fields of an-nual crops favor short-lived annual weeds,whereas maintaining land in perennial cropsfavors perennial weed species. Two exampleswould be shattercane in continuous sorghumand downy brome in continuous winter wheat.In a crop rotation, the timing of cultivation,mowing, fertilization, herbicide application,and harvesting changes from year to year. Ro-tation thus changes the growing conditionsfrom year to yeara situation to which fewweed species easily adapt. Rotations that in-clude clean-cultivated annual crops, tightly



spaced grain crops, and mowed or grazed pe-rennial sod crops create an unstable environ-ment for weeds. Additional weed control maybe obtained by including short-season weed-smothering crops such as sorghum-sudan orbuckwheat. Crop rotation has long been recog-nized for this ability to prevent weeds from de-veloping to serious levels.

In a dryland wheat study, continuous winterwheat was compared to a rotation of winterwheat/proso millet/fallow or a winter wheat/sunflower/fallow rotation (17). The year be-fore, at the start of the study, the fields were inwinter wheat and were sprayed withRoundup (glyphosate) and 2,4-D. The sun-flowers were treated with Prowl(Pendimethalin). All other weed control wasby mechanical means, including a sweep and

rodweeder as needed. During the two-yearstudy, weed levels were 145 plants per squareyard for the continuous wheat, 0.4 plants persquare yard for the winter wheat/proso milletfallow system, and 0.3 for the winter wheat/sunflower fallow system.

Intercropping

Intercropping (growing two or more crops to-gether) can be used as an effective weed con-trol strategy. Having different plant types grow-

ing together enhances weed control by increas-ing shade and increasing crop competition withweeds through tighter crop spacing. Where onecrop is relay-intercropped into another stand-ing crop prior to harvest, the planted crop getsoff to a weed-free start, having benefited fromthe standing crops shading and competitionagainst weeds. Such is the case when soybeansare interplanted into standing green wheatthe thick wheat stand competes well with weedswhile the soybeans are getting started. Plant-ing method, planting date, and variety must be

well-planned in advance. Though soybeans canbe directly drilled into the standing green wheat,less wheat damage occurs if the wheat isplanted in skiprows. Skiprows are created byplugging certain drop tube holes in the graindrill. Soybeans can be planted with row unitsset at spacings matched to the skiprows in thewheat. For example, if the wheat is drilled on7-inch rows, to create a 30-inch row spacingfor soybeans, every fourth drill hole in the wheat

drill would be plugged. Tractor tires will fol-low the skips, resulting in no damage to thewheat.

Studies in Missouri and Ohio showed that wheatyields were three to six bushels per acre lesswhen intercropped with soybeans than whensolid-drilled and grown alone (18). Generally,

soybean yields are higher when intercroppedinto wheat than when double cropped behindwheat in the central and northern Midwest,where double cropping is risky due to a shortergrowing season. For more information on in-tercropping, request the ATTRA publicationentitled Intercropping Principles and ProductionPractices.

Weed-Free by Design

Thus far, weve seen that weeds are a symptom

of land management that defies natures design.Stirring the soil with tillage creates conditionsfavorable for weed germination and survival.Monocultures of annual crops hold naturalplant succession back and minimize biodiversity,inviting weed populations to thrive. When wetry to maintain bare ground, weeds grow tocover the soil and increase biodiversity.

If we take a proactive approach to the wholeagricultural system, rather than just looking atthe parts, we can use the principles of nature toour advantage instead of fighting them. We willnever win the war against nature, and, she hasmuch more patience than we do. When we tryto break the rules of nature, we end up break-ing ourselves against the rules.

Lets look at an agronomic system wherebydesignweeds simply are not a problem. Oneof the biggest shortcomings in American agri-culture is the separation of plant and animalproduction. Commodity crop production of

corn, milo, and soybeans is really a componentof animal production because these crops arelargely fed to livestock. It seems inefficient togrow grains separately and haul them to ani-mal-feeding facilities. At Shasta College inRedding, California, Dr. Bill Burrows has de-veloped a series of complementary crop andanimal systems. He plants a mixture of miloand cowpeas together, with no herbicide. Themilo and cowpeas are so vigorous they
http://attra.ncat.org/attra-pub/intercrop.htmlhttp://attra.ncat.org/attra-pub/intercrop.htmlhttp://attra.ncat.org/attra-pub/intercrop.htmlhttp://attra.ncat.org/attra-pub/intercrop.htmlhttp://attra.ncat.org/attra-pub/intercrop.htmlhttp://attra.ncat.org/attra-pub/intercrop.html



outcompete any weeds present. Here naturesprinciple of biodiversity is obeyed rather thanfought with herbicides. Previously, when themilo was grown separately, he had to spray forgreenbugs. After he started with the pea-milomixture, the greenbug problem disappeared.When the milo and peas are mature, he com-bines them. This produces a milo to pea ratio

of 2/3 to 1/3, which is ideal for feed.

After grain harvest he turns his animal mixtureof hogs, cattle, sheep, and chickens into thestanding crop stubble, thereby adding more di-versity. All the waste grain is consumed by live-stock, and the stubble trampled into the soil, ata profit in animal gains to the farmer. Whatfew weeds may have grown up with the cropcan be eaten by the livestock. Under typicalsingle-crop scenarios, the waste grain would rot

in the field and the farmer might incur a$6/acre stalk mowing cost. In this case, fol-lowing the principle of biodiversity increasedprofit by lowering cost. Bill and his team de-signed weeds out of the system. Other oppor-tunities exist to design weeds out of the farm-ing operation. These opportunities are limitedonly by human creativitythe mostunderutilized tool in the toolbox.

Reactive Measures

The reactive paradigm of weed management istypified by the word control. This word assumesthat weeds are already present, or to be ex-pected, and the task is to solve the problemthrough intervention. Agriculture magazinesare chock-full of advertisements promising sea-son-long control, complete control, and controlof your toughest weeds. These ads imply thatthe secret is in the proper tank mix of herbi-cides. Examining these ads from a cause-and-effect standpoint, we might well conclude thatweeds are caused by a deficiency of herbicides

in the field.

When selecting a tool for weed management, ithelps to understand the weeds growth stagesand to attack its weakest growth stage (the seed-ling stage). Alternatively, management tech-niques that discourage weed seed germinationcould be implemented. In so doing, a farmercan identify a means of control that requires theleast amount of resources.

The various tools available for weed manage-ment fall into two categories: those that enhancebiodiversity in the field and those that reduce it(Table 7). This is not to imply a good vs. baddistinction. Rather it is meant to describe theeffect of the tool on this important characteris-tic of the crop/weed interaction. In general, asplant diversity increases, weeds become less of

a problem.

Weed Control Tools and Their Effects

Herbicides

Since herbicide information is abundantly avail-able from other sources, it is not covered in de-tail in this guide. Herbicides can be effective inmaintaining ground cover in no-till systems byreplacing tillage operations that would other-wise create bare ground and stimulate moreweed growth. Until better weed management

approaches can be found, herbicides will con-tinue to remain in the toolbox of annual cropproduction. However, some farmers are realiz-ing that with continued herbicide use, the weedproblems just get worse or at best stay aboutthe same. Nature never gives up trying to fillthe vacuum created by a simplified bare-groundmonoculture, and long-term use of the sameherbicide leads to resistant weeds, as they adaptto the selection pressure applied to them. Butcompared to tillage systems where bare groundis maintained, herbicide use may be considered

the lesser of two evils. At least where groundcover is maintained, the soil is protected fromerosion for future generations to farm. Thereare many approaches to reducing costly herbi-cide use, such as banding combined withbetween-row cultivation, reduced rates, andusing some of the other methods discussedearlier.



Least-toxic Herbicides

Corn gluten meal has been used successfully onlawns and high-value crops as a pre-emergentherbicide. It must be applied just prior to weedseed germination to be effective. A common rateis 40 pounds per 1000 square feet, whichsuppresses many common grasses andherbaceous weeds (19). Two name brand weed

control products containing corn gluten mealare WeedBan and Corn Weed Blocker.

Herbicidal soaps are available from RingerCorporation and from Mycogen. Scythe,produced by Mycogen, is made from fatty acids.Scythe acts fast as a broad-spectrum herbicide,and results can often be seen in as little as fiveminutes. It is used as a post-emergent, sprayeddirectly on the foliage.

Vinegar is an ingredient in several newherbicides on the market today. Burnout andBioganic are two available brands. Both ofthese are post-emergent burndown herbicides.They are sprayed onto the plant to burn off topgrowthhence the concept burndown. Asfor any root-killing activity with these twoherbicides, I cannot say. The label on Burnoutstates that perennials may regenerate after asingle application and require additionaltreatment.

Researchers in Maryland (20)tested 5% and 10%acidity vinegar for effectiveness in weed control.They found that older plants required a higherconcentration of vinegar to kill them. At thehigher concentration, they got an 85 to 100%kill rate. A 5% solution burned off the topgrowth with 100% success. Household vinegaris about 5% acetic acid. Burnout is 23% aceticacid. Bioganic contains 10% acetic acid plusclove oil, thyme oil, and sodium lauryl sulfate.AllDown Green Chemistry herbicide containsacetic acid, citric acid, garlic, and yucca extract.MATRAN contains 67% acetic acid and 34%clove oil. Weed Bye Bye contains both vinegarand lemon juice. Vinegar is corrosive to metalsprayer parts the higher the acidity, the morecorrosive. Plastic equipment is recommendedfor applying vinegar.

Dr. Jorge Vivanco of Colorado State Universityhorticulture department isolated the compoundcatechin, a root exudate from spotted

knapweed, Centaurea maculosa, that has strongherbicidal properties. Knapweed uses thecompound as an allelopathic method ofcompeting with other plants. Several companiesare interested in producing an environmentallyfriendly natural herbicide from the root exudate.Since catechin is naturally occuring, newherbicides made from it may be eligible for EPAs

fast-track approval process (21).

Weeder Geese

Weeder geese have been used successfully bothhistorically and in more recent times. They areparticularly useful on grass weeds (and someothers, too) in a variety of crops. Chinese orAfrican geese are favorite varieties for weedingpurposes. Young geese are usually placed inthe fields at six to eight weeks of age. They workwell at removing weeds between plants in rows

that cannot be reached by cultivators or hoes.If there are no trees in the field, temporary shadewill be needed. Supplemental feed and watermust be provided as well. Water and feed con-tainers can be moved to concentrate the geesein a certain area. A 24- to 30-inch fence is ad-equate to contain geese. Marauding dogs andcoyotes can be a problem and should be plannedfor with electric fencing or guard animals. Atthe end of the season, bring geese in for fatten-ing on grain. Carrying geese over to the next

season is not recommended, because older geeseare less active in hot weather than younger birds.Additionally, the cost of overwintering themoutweighs their worth the next season. Geesehave been used on the following crops: cotton,strawberries, tree nurseries, corn (after lay-by),fruit orchards, tobacco, potatoes, onions, sugarbeets, brambles, other small fruits, and orna-mentals. ATTRA can provide more informa-tion on weeder geese.

Til lage

Tillage and cultivation are the most traditionalmeans of weed management in agriculture.Both expose bare ground, which is an invitationfor weeds to grow. Bare ground also encouragessoil erosion, speeds organic matterdecomposition, disturbs soil biology, increaseswater runoff, decreases water infiltration,damages soil structure, and costs money tomaintain (for fuel and machinery or for handlabor). Some specific tillage guidelines and



techniques for weed management include thefollowing:

Preplant tillage. Where weeds such asquackgrass or johnsongrass exist, spring-toothharrows and similar tools can be effective incatching and pulling the rhizomes to the soilsurface, where they desiccate and die. Discing,

by contrast, tends to cut and distribute rhizomesand may make the stand even more dense.

Blind tillage. Blind cultivation is a pre-emer-gent and early post-emergent tillage operationfor weed control. It usually employs either fin-ger weeders, tine harrows, or rotary hoes. Theseimplements are run across the entire field, in-cluding directly over the rows. The large-seededcorn, soybeans, or sunflowers survive with mini-mal damage, while small-seeded weeds are eas-ily uprooted and killed. For corn, the first passshould be made between three and five daysafter planting and a second at the spike stage.Blind cultivation may continue until the crop isabout five inches tall. For soybeans, the firstpass should be done when germinating cropseedlings are still about inch below the soilsurface, but not when the hook is actuallyemerging. The second pass should be done threeto five days after soybean emergence, and twicelater at four-day intervals. Sunflowers can beblind-tilled up to the six-leaf stage, giving them

an excellent head start on weeds. Grain sor-ghum may be rotary hoed prior to the spikestage, and again about one week after spikestage. Because the seed is small, timing forblind-till in sorghum is very exacting. Post-emer-gent blind tillage should be done in the hottestpart of the day, when crop plants are limber, toavoid excessive damage. Rotary hoes, not har-rows, should be used if the soil is crusted or tootrashy. Seeding rates should be increased 5 to10% to compensate for losses in blind cultiva-tion (22, 23).

Row crop cultivation. Cultivation is best keptas shallow as possible to bring as few weed seedsas possible to the soil surface. Where perennialrhizome weeds are a problem, the shovels far-thest from the crop row may be set deeper onthe first cultivation to bring rhizomes to the sur-face. Tines are more effective than duck feetsweeps for this purpose. Later cultivationsshould have all shovels set shallow to avoid ex-

cessive pruning of crop roots. Earliest cultiva-tion should avoid throwing soil toward the croprow, as this places new weed seed into the croprow where it may germinate before the cropcanopy can shade it out. Use row shields asappropriate. As the crop canopy develops, soilshould be thrown into the crop row to coveremerging weeds.

Interrow cultivation is best done as soon aspossible after precipitation, once the soil isdry enough to work. This avoids compaction,breaks surface crusting, and catches weeds asthey are germinatingthe most vulnerablestage.

Generally speaking, tillage systems tend to dis-courage most biennial and perennial weed spe-cies, leaving annual weeds as the primary prob-lem. Exceptions to this are several weeds withespecially resilient underground rhizome struc-tures such as johnsongrass, field bindweed, andquackgrass. Plowing of fields to bring up therhizomes and roots has been used to controlbindweed and quackgrass.

Another interesting application of timing toweed control is night tillage. Researchers havefound that germination of some weed species isapparently triggered by exposure to light. Till-age done in darkness exposes far fewer seeds to

light and reduces weed pressure. So far, small-seeded broadleaf weeds (lambsquarter, rag-weed, pigweed, smartweed, mustard, and blacknightshade) appear to be most readily affected(24).

Flam e w eedi ng

Preplant, pre-emergent, and post-emergentflame weeding has been successful in a numberof crops. The preplant application has com-monly been referred to as the stale seedbedtechnique. After seedbed tillage is completed,

weed seeds, mostly in the upper two inches ofthe soil, are allowed to sprout. Assuming ad-equate moisture and a minimum soil tempera-ture of 50 F (to a depth of 2 inches), this shouldoccur within two weeks. A fine to slightly com-pacted seedbed will germinate a much largernumber of weeds. The weeds are then searedwith a flamer, or burned down with a broad-spectrum herbicide, preferably when thepopulationInsteIn, Instead, the ridge-till planter



population is between the first and fifth true-leaf stages, a time when they are most suscep-tible. The crop should then be seeded as soonas possible, and with minimal soil disturbanceto avoid bringing new seed to the surface. Forthe same reason, subsequent cultivations shouldbe shallow (less than 2 inches deep)(25).

Pre-emergent flaming may be done after seed-ing, and in some crops post-emergent flamingmay be done as well. Flaming is often used asa band treatment for the crop row, and usuallycombined with interrow cultivation. Earlyflaming may be done in corn when it is 1.5 to 2inches high. The growing tip is beneath thesoil surface at this stage, and the crop readilyrecovers from the leaf damage. Subsequentpost-emergent flamings may be done when cornreaches 610 inches in height, and later at lay-

by. No flaming should be done when corn is atapproximately 4 inches high, as it is most vul-nerable then. The burners are offset to reduceturbulence and to avoid concentrating toomuch heat on the corn. Water shields are avail-able on some flame weeder models. Uniformseedbed preparation and uniform tractor speedare important elements in flaming. Hot anddry weather appears to increase the efficacy offlaming (26).

Searing the plant is much more successful than

charring. Excessive burning of the weeds of-ten stimulates the roots and encourages re-growth, in addition to using more fuel. Flam-ing has generally proved most successful onyoung broadleaf weeds. It is reportedly lesssuccessful on grasses, as the seedlings developa protective sheath around the growing tipwhen they are about 1 inch tall (27). Some con-cerns with the use of fire include possible cropdamage, potential dangers in fuel handling, andthe cost of fuel. For more information on flameweeding, see the ATTRA publication FlameWeeding for Agronomic Crops.

Integrated Weed Management

An integrated approach means assembling aweed management plan that incorporates anumber of tools consistent with farm goals.Included are sanitation procedures, croprotations, specialized tillage schemes, covercrops, and herbicides. The best examples of

integrated approaches have been developed on-farm, by farmers themselves. A useful bookthat spotlights farmers and other researchersand the integrated weed management strategiesthey are using is Controlling Weeds With FewerChemicals, available from the Rodale Institute(see Additional Resources). The next two

examples are taken from this book.

Dick and Sharon Thompson of Boone, Iowa,built a herbicide-free weed-management sys-tem around ridge-till technology for corn andsoybeans. Fields are overseeded or drilled inthe fall with combinations of hairy vetch, oats,and grain rye as a winter cover crop. The vetchprovides nitrogen, while the grasses provideweed suppression and erosion protection. Thecover crop is not tilled in before planting.
http://attra.ncat.org/attra-pub/PDF/flameweed.pdfhttp://attra.ncat.org/attra-pub/PDF/flameweed.pdfhttp://attra.ncat.org/attra-pub/PDF/flameweed.pdfhttp://attra.ncat.org/attra-pub/PDF/flameweed.pdfhttp://attra.ncat.org/attra-pub/PDF/flameweed.pdf



skims off enough of the ridge top to create aclean seeding strip. Subsequent passes with theridge-till cultivator eliminate any cover crop inthe interrow area and help to re-shape theridges. The Thompsons estimate savings of $45to $48 per acre using their methods. Walkingthe Journey is a 20-minute video chroniclingthe Thompson farm, available for $39. See Ad-

ditional Resourcesfor ordering information.

In Windsor, North Dakota, Fred Kirschen-mann has developed a diverse rotation includ-ing cool-weather crops like oats, rye, barley, andspring wheat, and warm-season crops like sun-flower, buckwheat, and millet. He employs se-lective timing to manage his principal weedproblem, pigeon grass. By planting cool-weather grains early, he can get a competitivejump on the weed, which requires somewhat

warmer soil to germinate. The warm-seasoncrops do best long after pigeon grass has germi-nated, however. He uses shallow pre-plant till-age to control weeds in these crops.Kirschenmann also composts manure beforespreading it. One of the many advantages ofcomposting is the reduction of viable weedseeds, which are killed by heat during thecuring process.

Don and Deloris Easdale of Hurdland, Missouri,reduced their annual herbicide costs from

$10,000 to less than $1,000 in three years ontheir 300-plus acres of grain crops (28). Theyuse hairy vetch, winter rye, or Austrian winterpeas in combination with their ridge-till system.They flail chop hairy vetch or winter peas aheadof the ridge-till planter and plant directly intothe remaining cover crop residue. This practiceeliminates using a burndown herbicide. Thelegumes replace much of the nitrogen neededfor the corn or milo crop. Some liquid starterand liquid nitrogen is placed below the seed atplanting. They more than recover the seed costsof their cover crops in savings on fertilizer andherbicide.

Other ATTRA Publications of Interest

Cover Crops and Green ManuresUses, benefits, and limitations of cover cropsand green manures; vegetation manage-ment; and sources of information.

Sustainable Soil ManagementAssessing soil health; organic matter andhumus management; organic amendments;soil organisms; aggregation; fertilizers;addtional resources.

Sustainable Corn and Soybean ProductionWeed, seed, and pest management; strip crop

ping; farm experiences.

Making the Transition to SustainableFarmingPlanning, key ideas for transitions, andpractices.

Pursuing Conservation Tillage for OrganicCrop ProductionA look at the potential for applying conservationtillage to organic cropping systems.

The following Current Topics are also available:

Conservation Tillage Alternative Control of Johnsongrass Alternative Control of Field Bindweed

References

1) Barker, Joel A. 1993. ParadigmsTheBusiness of Discovering the Future. HarperBusiness. New York. 240 p.

2) Savory, Allan. 1988. Holistic ResourceManagement. Island Press. Washington,DC. 564 p.

3) Wilson, Robert G. 1988. Biology of weedseeds in the soil. p. 2540. In: Miguel Altieriand Matt Liebman (eds.). Weed Manage-ment in Agroecosystems: Ecological Ap-proaches. CRC Press, Inc. Boca Raton, FL.354 p.

4) Stevens, O.A. 1954. Weed Seed Facts. NorthDakota Agriculture College ExtensionCircular. A-218. 4 p.

5) Lehnert, Dick. 1996. Breaking the weed-seed bank. Soybean Digest. Mid-March.p. 52.
http://attra.ncat.org/attra-pub/soilmgmt.htmlhttp://attra.ncat.org/attra-pub/cornbean.htmlhttp://www.geocities.com/RainForest/7813/sa-trans.htmhttp://www.geocities.com/RainForest/7813/sa-trans.htmhttp://attra.ncat.org/attra-pub/PDF/omconservtill.pdfhttp://attra.ncat.org/attra-pub/PDF/omconservtill.pdfhttp://attra.ncat.org/attra-pub/conservationtillage.htmlhttp://attra.ncat.org/attra-pub/PDF/johnson.pdfhttp://attra.ncat.org/attra-pub/bindweed.htmlhttp://attra.ncat.org/attra-pub/bindweed.htmlhttp://attra.ncat.org/attra-pub/PDF/johnson.pdfhttp://attra.ncat.org/attra-pub/conservationtillage.htmlhttp://attra.ncat.org/attra-pub/PDF/omconservtill.pdfhttp://attra.ncat.org/attra-pub/PDF/omconservtill.pdfhttp://www.geocities.com/RainForest/7813/sa-trans.htmhttp://www.geocities.com/RainForest/7813/sa-trans.htmhttp://attra.ncat.org/attra-pub/cornbean.htmlhttp://attra.ncat.org/attra-pub/soilmgmt.html



6) Clements, David R., Diane L. Benoit, StephenD. Murphy, and Clarence J. Swanton. 1996.Tillage effects on weed seed return andseedbank composition. Weed Science. Vol-ume 44. p. 314322.

7) Schlesselman, John T., Gary L. Ritenour, andMahlon Hile. 1989. Cultural and physical

control methods. p. 4562. In: Principles ofWeed Control in California. Second edition.California Weed Conference. ThompsonPublications. Fresno, CA.

8) Daar, Sheila. 1986. Update: Suppressingweeds with allelopathic mulches. The IPMPractitioner. April. p. 14.

9) Putnam, Alan R., Joseph DeFrank, and JaneP. Barnes. 1983. Exploitation of allelopa-

thy for weed control in annual and peren-nial cropping systems. Journal of ChemicalEcology. Volume 9, Number 8. p. 10011010.

10) Worsham, A.D. 1991. Allelopathic covercrops to reduce herbicide input. Proceed-ings of the Southern Weed Science Society.44th Annual. Volume 44. p. 5869.

11) Schilling, D.G., A.D. Worsham, and D.A.Danehower. 1986. Influence of mulch, till-

age, and diphenamid on weed control, yield,and quality in no-till, flue-cured tobacco.Weed Science. Volume 34. p. 738744.

12) Yenish, J.P., and A.D. Worsham. 1993.Replacing herbicides with herbage: poten-tial use for cover crops in no-tillage. p. 37-42. In: P.K. Bollich, (ed.) Proceedings ofthe Southern Conservation Tillage Confer-ence for Sustainable Agriculture. Monroe,LA. June 1517.

13) Anon. 1993. Sweet potato plants vs. weeds.HortIdeas. January. p. 8.

14) Boydston, Rick, and Ann Hang. 1995.Rapeseed green manure crop suppressesweeds in potato. Weed Technology. Vol. 9.p. 669675.

15) University of Connecticut IPM Program.No date. Contribution of cover cropmulches to weed management..

16) Crutchfield, Donald A., Gail A. Wicks, andOrvin C. Burnside. 1985. Effect of winterwheat straw mulch level on weed control.

Weed Science. Volume 34. p. 110114.

17) Lyon, Drew J., and David D. Baltensperger.1995. Cropping systems control winter an-nual grass weeds in winter wheat. Journalof Production Agriculture. Vol. 8, No. 4. p.535539.

18) Helsel, Z.R. and T. Reinbott. Circa 1989.Intercropping: planting soybeans into stand-ing green wheat. University of Missouri

Agronomy Department. University of Mis-souri, Columbia, MO. 3 p.

19) Quarles, William. 1999. Non-toxic weedcontrol in the lawn and garden. CommonSense Pest Control Quarterly. Summer. p.414.

20) Anon. 2002. Vinegar wipes out thistlesorganically. Stockman Grass Farmer. July.p. 1.

21) Malone, Marty. 2003. Uses for Knapweed?The Ag Perspective. Park County Exten-sion Service. Available online at:http://www.parkcounty.org/Extension/News/Weed_news/weed_news.html.

22) Anon. 1991. Non-chemical weed controlfor row crops. Sustainable Farming News.September. p. 18.

23) Jordan, C. Wayne. 1981. Sunflower Pro-duction In Mississippi. Cooperative Exten-sion Service. Mississippi State University.Mississippi State, MS. 2 p.

24) Becker, Hank. 1996. Nightmare in tillingfieldsa horror for weeds. Farmers Digest.March. p. 2024.

25) Pieri, Paul B. No date. Flame Weeding.Maurolou Farm. Little Compton, RI. 6 p.
http://www.hort.uconn.edu/ipm/http://www.parkcounty.org/Extension/News/Weed_news/weed_news.htmlhttp://www.parkcounty.org/Extension/News/Weed_news/weed_news.htmlhttp://www.parkcounty.org/Extension/News/Weed_news/weed_news.htmlhttp://www.parkcounty.org/Extension/News/Weed_news/weed_news.htmlhttp://www.hort.uconn.edu/ipm/



26) Cramer, Craig. 1990. Turbocharge your cul-tivator. New Farm. MarchApril.p. 2730, 35.

27) Drlik, Tanya. 1994. Non-toxic weed con-trol. The IPM Practitioner. October. p. 20.

28) Easdale, Deloris. 1996. Controlling weeds

and maintaining soil fertility with covercrops. National Conservation Tillage Digest.February. Vol. 3, No. 2. p. 2830.

Additional Resources

Shirley, C., and New Farm staff. 1993. WhatReally Happens When You Cut Chemicals.February. Vol. 3, No. 2. p. 2830. 156 p.

This book contains a series of farmers ex-periences with adopting new strategies forhigher profits and lower input costs, while

enhancing the environment. Available for$14.95 from:

Rodale Institute611 Siegfriedale RoadKutztown, PA 19530800-832-6285610-683-6009http://www.rodaleinstitute.orgE-mail: [email protected]

Cramer, Craig, and the New Farm Staff (eds.).1991. Controlling Weeds with Fewer Chemi-cals. Rodale Institute, Kutztown, PA. 138 p.

Available for $14.95 from Rodale Institute (seeaddress above).

Bowman, Greg (ed.). 1997. Steel in the Field.Sustainable Agriculture Network Handbook

# 2. 128 p.This book is a farmers guide to weed manage-ment tools using cultivation equipment. Avail-able for $18.00 + $3.95 shipping and handlingfrom the Rodale Institute listed above or:

Sustainable Agriculture Publications210 Hills BuildingUniversity of VermontBurlington, VT 05405-0082802-656-0484E-mail: [email protected]

http://www.sare.org/htdocs/pubs/

Walking the Journey: Sustainable Agriculturethat Works. 1992.

A 20minute video of Dick and SharonThompsons ridge-till farming in Iowa.Available for $25 from:

Extension CommunicationsAttention: Lisa Scarborough3614 ASB, Room 1712Iowa State University

Ames, IA 50011515-294-4972
http://www.rodaleinstitute.org/mailto:[email protected]:[email protected]://www.sare.org/htdocs/pubs/http://www.sare.org/htdocs/pubs/mailto:[email protected]:[email protected]://www.rodaleinstitute.org/


15/15

FeedbackFeedbackFeedbackFeedbackFeedback1. Does this publication provide the information you were look-

ing for? How could it be improved?

2. Do you know a farmer who is implementing techniques dis-cussed in this publication? Can you provide their addressand phone number?

3. Do you know of any related research that would add to theinformation presented here?

4. Do you know a good related website not listed in this publi-cation?

5. Please add any other information or comments that you would

wish to share.

Documents

Book Weed Management