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Pest Management & Crop Development Bulletin • No. 6 / May 3, 2002

FOR IMMEDIATE RELEASENo. 6 / May 3, 2002

Executive editor: Kevin Steffey,Extension Entomologist

Available on the Web athttp://www.ag.uiuc.edu/cespubs/pest/For subscription information, phone

217.244.5166, or e-mailacesnews@uiuc.edu

Copyright © 2002, Board of Trustees,

University of Illinois

In This Issue

❏ Estimating Alfalfa Quality inthe Field, 61

❏ White Grubs and WirewormsCan Injure Slow-GrowingCorn, 61

❏ More Reports of MothCaptures—Armyworms andBlack Cutworms, 62

❏ Bean Leaf Beetles Are Active,62

❏ Alfalfa Weevils CreatingHeadaches in Many Fields, 63

❏ Don’t Confuse Clover LeafWeevils with Alfalfa Weevils,64

❏ And More!

INSECTS

Estimating Alfalfa Quality in the Field

When to take the first cutting of alfalfa is an important question for thosedesiring to harvest high-quality hay or haylage. Estimating the relative feedvalue (RFV) of standing alfalfa can be accomplished by using PEAQ (pre-dictive equations for alfalfa quality), a system developed at the University ofWisconsin and used in Illinois the past few years.

PEAQ is a function of plant height (soil surface to stem tip) and stage ofmaturity (vegetative, bud, or flower). From these two factors, the estimatedRFV of standing alfalfa is obtained. PEAQ can be determined by using ayardstick and a table, or a PEAQ measuring stick available from many al-falfa seed dealers and companies.

You are encouraged to check the Illini PEAQ Web site at http://peaq.outreach.uiuc.edu/. At this Web site you can learn how to calculatePEAQ, view PEAQ values for Illinois (by region and by county), enter andtrack your own PEAQ values, and so on.

As a general guide, if 150 RFV alfalfa hay is desired, harvest when PEAQindicates 170 RFV. Many times RFV will drop 3 to 5 points per day.

PEAQ is designed for 16- to 42-inch-tall alfalfa, but it is not intended tobalance rations. It does not account for quality changes due to wilting, har-vesting, and storage. The procedure is most accurate for good stands of purealfalfa with healthy growth.—Jim Morrison

White Grubs and Wireworms Can Injure Slow-Growing Corn

The report from the Illinois Agricultural Statistics Service (http://www.agstats.state.il.us/), issued for the week ending April 28, indicated that25% of the corn crop in Illinois had been planted, and only 5% had emerged.Wet weather has delayed planting in many areas, and cool soils are not en-couraging rapid corn growth. Consequently, subterranean insects such aswhite grubs and wireworms can ravage slow-growing corn seedlings.

I have reported that many people have observed large numbers of whitegrubs (primarily Japanese beetle grubs) this season, so it’s only a matter oftime before we start to receive more reports of injury to corn. Although Ihaven’t said much thus far about wireworms, they are causing a few prob-lems as well. Entomologists at the University of Kentucky have receivedreports of serious wireworm activity. Not surprisingly, our first report ofwireworm activity in Illinois came from a southern county. Dale Burmester,crop specialist with Gateway FS in Redbud, found a lot of wireworms in afield near Sparta (Randolph County).

As folks wait anxiously to resume planting corn, don’t forget the corn al-ready in the ground. Check fields for wilted and/or missing plants, signs ofinjury by underground insects. Keep in mind that other factors can causesimilar injury, so you have to find the culprits to blame the problem on whitegrubs or wireworms. Considering the numbers of these pests that have beenreported thus far, finding them shouldn’t be too difficult.

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Unfortunately, because there are norescue treatments of insecticides thatwill control white grubs or wire-worms, fields that are heavily infestedmay have to be replanted. Both typesof pests will remain a threat into mid-May, after which concern about theirfeeding will diminish.—Kevin Steffey

More Reports of MothCaptures—Armyworms andBlack Cutworms

A lot of people throughout the Mid-west have reported captures of army-worm and black cutworm moths allspring. Always remember that al-though these captures offer someinsight about the timing of mothflights, large captures do not alwaysrelate to outbreaks of the respectivelarvae. Many factors can cause mortal-ity to eggs and young larvae of botharmyworms and black cutworms, soinfestations often don’t materialize,even if large numbers of adults havebeen captured. That having been said,stay alert for both insects. Both arecapable of causing serious damagerather quickly.

The folks at the Missouri Delta Re-search Center reported an enormouscapture of armyworm moths (1,093) inMississippi County (the “bootheel”)on April 24. Entomologists at PurdueUniversity reported a capture of 280moths in a blacklight trap operating innorth-central Indiana between April 16and 22. Fewer armyworm moths havebeen captured in pheromone traps insouthern Illinois, but we are stillwatching them closely (see “TheHines Report,” http://ipm.uiuc.edu/publications/hines-report).

Dale Burmester, crop specialist withGateway FS in Redbud, has foundevidence of a little feeding activity bysmall armyworm larvae in wheat. RonHines, senior research specialist at theUniversity of Illinois Dixon SpringsAgricultural Center, has found smallarmyworm larvae in grass hay fieldsin Massac, Pope, and Pulaski counties.These early reports of small larvae

should be noted. Although it’s unlikelythat we will experience an outbreaksimilar to the outbreak in 2001, itnever hurts to be prepared.

Intense captures of black cutwormshave been reported from many loca-tions. But quite honestly, predictingthe dates of first cutting activity (300accumulated degree-days after anintense capture) makes little senseright now. Any corn that has emergedshould be monitored carefully now forblack cutworms and signs of theirinjury. The same will hold true forcorn that will be planted soon. Re-member, the potential for black cut-worm damage increases significantlywhen corn is planted late, after themoths have had time to find egg-laying sites.—Kevin Steffey

Bean Leaf Beetles Are Active

Several entomologists have reportedfinding bean leaf beetles recentlyactive in alfalfa and clover fields andin noncrop areas. Although very fewsoybeans have been planted yet thisyear, any early-planted fields shouldbe monitored very carefully as soon asplants emerge. These early fields willbe “magnets” for bean leaf beetles.

Bean leaf beetles overwinter as adults,becoming active in the spring soonafter the temperature rises above 50 to55ºF. They fly first to alfalfa and clo-ver fields where males and femalesmate. However, the females do not layeggs in alfalfa and clover. As soon assoybean seedlings emerge, the beetlesabandon the forage fields and colonizesoybean fields. They feed on emergingseedlings and deposit eggs in the soilnear the plants.

Because bean leaf beetle adults over-winter above ground, their survivalthrough the winter hinges on wintertemperatures. Research and Extensionentomologists at Iowa State Universityhave accumulated some really goodstuff regarding survival (or mortality)of bean leaf beetles through the winter.Broadly stated, bean leaf beetle mor-

tality is less during mild winters thanduring winters with plenty of coldtemperatures. The entomologists atIowa State University have compiled atable of bean leaf beetle mortality,from 1989 through 2001 (http://www.ipm.iastate.edu/ipm/icm/2001/5-7-2001/blbsurvival.html). In the ar-ticle, they explain how they developedthe model to predict mortality of beanleaf beetles. Average beetle mortalityin central Iowa during this period was71%. Average beetle mortality in cen-tral Iowa from the 2001–2002 winterwas only 48% (http://www.ipm.iastate.edu/ipm/icm/2002/4-29-2002/blbwinter.html). If the infor-mation from Iowa is any indication ofsurvival of bean leaf beetles in Illinoisthis year, we'd better be ready.

Bean leaf beetles are about 1/4 inchlong, with considerable variation incolor pattern. Most bean leaf beetlesare light yellow to tan, but they maybe red. Wing covers may have fourmain black spots and stripes, but thesemarkings may be absent. However, ablack triangle is always present behindthe prothorax (“neck”).

If large numbers of bean leaf beetlesfeed on newly emerged soybean seed-lings, the damage can be severe. Feed-ing on VE (plant emergence) and VC(expansion of the unifoliolate leaves)can result in plant death and reducedstands. As soon as the first trifoliolateemerges, the soybean plant is betterequipped to compensate for injury tothe foliage. Nevertheless, large num-bers of bean leaf beetles can over-whelm small soybean plants.

Economic thresholds for bean leafbeetles are much higher now than theywere a few years ago, based on re-search conducted at the University ofNebraska. Densities of 16 per foot ofrow in the early seedling stage or 39per foot of row at stage V2+ are neces-sary before economic losses occur. I’lloffer a list of insecticides suggestedfor control of bean leaf beetles insoybeans in a forthcoming issue of theBulletin.

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Much of the concern about bean leafbeetles in recent years has resultedfrom the discovery that the beetles cantransmit bean pod mottle virus. How-ever, although research regarding thedisease and the insect is being con-ducted in several midwestern states,definitive results have yet to be deter-mined. Following is information takenverbatim from the May 14, 2001, issueof Iowa State University’s IntegratedCrop Management:

“However, we do not know whatpercentage of beetles carry theliving virus in their gut when theyemerged. The virus may not over-winter very well inside the beetle.Studies conducted by Craig Grau,plant pathologist at University ofWisconsin, suggest that alfalfa mayharbor bean pod mottle virus so itwould be relatively easy for beetlesto acquire the virus from alfalfabefore moving to soybean.

“The rise of bean leaf beetle popu-lations and bean pod mottle virusproblems during the past 2–3 yearsalso strongly suggests that we mayneed to manage our early-seasonbean leaf beetle population muchdifferently than we did in the1990s. We are researching the beanleaf beetle–bean pod mottle virusproblem but we have few solidanswers regarding management atpresent. However, some soybeanfields, especially very early emerg-ing fields, may benefit from anearly-season insecticide applicationduring the VC–V2 stages to controlbean leaf beetles, which would thenhelp reduce viral infection.”

There’s still a lot to learn about beanleaf beetles and bean pod mottle virus.Let’s keep this in perspective.—KevinSteffey

Alfalfa Weevils CreatingHeadaches in Many Fields

By now it’s no secret that alfalfa wee-vils have caused more damage toalfalfa this year than in several recent

years. They survived the mild winterconditions quite well, and they seemedto come on early and strong in mostareas. Alfalfa weevils have been activein southern Illinois for a few weeks.During the week of April 22, alfalfaweevils captured a great deal of atten-tion as far north as I-80. Entomolo-gists at Purdue University reportedhigh densities of alfalfa weevils inwest-central and northwestern Indianaduring the same week.

On April 24, Kevin Black, withGrowmark, reported that 50 to 100%of alfalfa plants were infested withalfalfa weevils in Ford County. KevinForeman, with Crop Production Ser-vices, reported that spraying for alfalfaweevil control began in HendersonCounty on April 25. It’s apparent fromthese reports that scouting for alfalfaweevils in central counties shouldhave been initiated well before now.So, I strongly encourage people innorthern counties to look for weevilactivity in their alfalfa fields.

The maps of actual degree-day accu-mulations (Figure 1) and projecteddegree-day accumulations (Figure 2)pretty much tell the story. Based onactual degree-day accumulations,alfalfa weevils should be evidentthroughout the state, although thelarvae should be rather small in north-ern counties. In southern Illinois, thesecond peak of larvae from spring-deposited eggs (~575 degree-days[base 48ºF] from January 1) should beoccurring. Omar Koester, Monroe/Randolph Extension unit assistant incrop systems, observed newly hatchedlarvae on April 30.

Omar Koester also reported that, inalfalfa fields that were sprayed too late(after the weevils had caused exten-sive damage) or not sprayed at all, thefirst cutting is virtually lost. In thesefields, he noticed new growth from thecrowns. The absence of foliage andthe penetration of sunlight have initi-ated this new growth. In fields with

Figure 1. Actual degree-day accumu-lations (base 48ºF), from January 1through April 29, 2002. (Map cour-tesy of Bob Scott, Illinois State WaterSurvey.)

Figure 2. Projected degree-day accu-mulations (base 48ºF), from January 1through May 12, 2002. (Map courtesyof Bob Scott, Illinois State WaterSurvey.)

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little foliage left, chickweed has“taken over” if herbicides were notused.

Shortly after I had submitted my ar-ticle about alfalfa weevils to the editorlast week, I received a report (April24) from Doug Kirkbride, M & JFertilizer, that alfalfa weevil larvaewere dying in some alfalfa fields inChristian County. He indicated thatthe larvae were brown and that thepopulation was “crashing.” It’s prob-able that the larvae Doug found wereinfected by the fungus Zoophthoraphytonomi, which I discussed in lastweek’s issue (no. 5, April 26, 2002) ofthe Bulletin. Although I have not re-ceived other, similar reports about Z.phytonomi, I encourage you to keepyour eyes peeled. The cool, wetweather is ideal for this pathogen, andan epizootic can overcome alfalfaweevil populations very quickly.

Scouting tips, thresholds, and sug-gested insecticides have been dis-cussed thoroughly in previous issuesof the Bulletin. However, I haven’tmentioned that an alternative to apply-ing insecticides is early harvest, whichis almost as effective at reducing num-bers of alfalfa weevil larvae as someinsecticides. If a producer intends toharvest early to avoid using an insecti-cide, make certain that yield and qual-ity of the alfalfa are not compro-mised.—Kevin Steffey

Don’t Confuse Clover LeafWeevils with Alfalfa Weevils

Matt Montgomery, Sangamon/MenardExtension unit educator in crop sys-tems, has reported finding clover leafweevils in some alfalfa fields in south-ern Sangamon County. Kevin Black,with Growmark, also has found cloverleaf weevils in some fields of alfalfaand red clover. Although clover leafweevils rarely cause economic dam-age in alfalfa in Illinois, their presenceshould be noted because they can beconfused with alfalfa weevils.

Although somewhat similar in appear-ance to both larvae and adults, clover

leaf weevils and alfalfa weevils havedistinctly different characteristics:

• The larvae of both species aregreen with a white stripe along thecenter of the back. However, thewhite stripe on the clover leaf wee-vil is bordered with smudges ofpink or red.

• The head of a clover leaf weevillarva is tan; the head of an alfalfaweevil larva is dark brown.

• A fully grown clover leaf weevillarva is about 1/2 inch long; a fullygrown alfalfa weevil larva is about3/8 inch long.

• An adult clover leaf weevil (5/16inch long) is about two times largerthan an adult alfalfa weevil (3/16inch long).

• An adult clover leaf weevil is lightbrown on the sides with a wide,dark brown stripe on the back. Anadult alfalfa weevil is brown with anarrow dark stripe along the centerof the wing covers.

Comparative photographs of these twospecies can be found in the April 27,1997, issue of Iowa State University’sIntegrated Crop Management (http://www.ipm.iastate.edu/ipm/icm/1997/4-21-1997/aflweevil97.html).

Clover leaf weevils and alfalfa weevilsalso feed and behave differently. Clo-ver leaf weevil larvae feed at night,usually on lower leaves. They can befound on the ground around thecrowns during the day. Alfalfa weevillarvae feed actively on alfalfa foliage,starting near the tips, during the day.

Don’t confuse the two species. Includ-ing counts of clover leaf weevils withcounts of alfalfa weevils could inflatethe estimate of the alfalfa weevilpopulation.—Kevin Steffey

A Few Insect “Thumbnail”Reports

Following are a few brief reports ofoccurrences of a few insects in Illinoisor elsewhere in the Midwest. More

detailed articles about some of theseinsects will be provided in forthcom-ing issues of the Bulletin.

• Ron Hines, senior research special-ist at the University of IllinoisDixon Springs Agricultural Center,captured the first European cornborer moth of the year in PulaskiCounty during the week of April23–30. The first capture of a Euro-pean corn borer moth in 2001 wason May 1.

• Leellen Solter, insect pathologistwith the Illinois Natural HistorySurvey, evaluated samples of over-wintering European corn borerlarvae for disease organisms. Thesamples from DeKalb and Fordcounties were gathered by KevinBlack, with Growmark. The resultsfrom DeKalb County—67% dis-ease free, 16% infected with themicrosporidum Nosema pyrausta,11% with symptoms of infection byBeauveria bassiana. The resultsfrom Ford County—74% diseasefree, 15% infected with themicrosporidum Nosema pyrausta,11% with symptoms of infection byBeauveria bassiana. Nosemapyrausta does not kill overwinter-ing borers; rather, the infectionpasses to the emerging adults, andinfected females lay fewer eggs.Beauveria bassiana is a fungusorganism that infects many insects,including European corn borers.Entomologists at Iowa State Uni-versity found a large percentage ofoverwintering European corn bor-ers killed by B. bassiana.

• Southern corn leaf beetles havebeen found feeding in cornfields inwestern and southwestern Missouri.After many years of silence, thispest has become more common inIllinois, Kansas, Missouri, andelsewhere in recent years. I’ll writean article about this pest in nextweek’s issue of the Bulletin.

• Dale Burmester, crop specialistwith Gateway FS at Redbud, foundwheat curl mites in wheat inRandoph County. These mites

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vector wheat streak mosaic virus.Although not commonly problem-atic, this disease has caused signifi-cant injury in southern counties inthe recent past.

• Large densities of bird-cherry oataphids have been found inorchardgrass in west-central andsouthwestern Missouri. Refer tolast week’s Bulletin (issue no. 5,April 26, 2002) for more informa-tion about the bird cherry-oataphid.

Keep looking and reporting. I’ll in-clude your information in the Bulletinso that others can benefit from yourobservations.—Kevin Steffey

Now Is the Time to Sample forPlant-Parasitic Nematodes

Q. Who should take soil samples?

A. Every crop grown in Illinois maybe affected by some species of plant-parasitic nematodes (PPNs). PPNsshould not be the last thing on yourlist of things to check if you aren’tgetting the yields you want or expectfrom your crop. The most damagingPPNs in Illinois are, of course, thesoybean cyst nematode and certainspecies of corn nematodes, but that’smostly because there are so manyacres of those two crops. Even home-owners, with their crops of lawn andlandscape plants, are subject to thedepredations of PPNs on their high-value plants. The best time to takedetection samples (those we use todetect whether a problem with PPNsmight exist) is in the spring.

Q. What are the symptoms of PPNinfestation?

A. If plant-parasitic nematode popula-tions are high enough to reduce plantgrowth or yield, most plants will shownonspecific symptoms, meaning thatyou can’t tell exactly what’s wrongwith the plants by looking at them.Soybeans, corn, vegetables, and otherannual crops may show stunting or

chlorosis. Perennials and trees mayhave an unthrifty appearance. It isimportant to note that these symptomsmay not be obvious unless there areunaffected plants (resistant or unin-fected) nearby for comparison. PPNsare often referred to as “the hiddenenemy” because they are difficult orimpossible to diagnose in the field.The only way to tell if they’re presentin high enough numbers to causedamage is to submit a soil sample formicroscopic analysis. If you had amysterious problem with growth oryield last year or the year before, takesamples this spring to see if the prob-lem might be PPNs.

Q. Where should soil samples betaken?

A. For annual or perennial field crops,a soil sample should be taken in azigzag pattern across a field. Mostnematologists agree that one samplecan adequately represent a 5-acre area;some say as high as 20 acres. So, whatdo you do if you have 300 acres?Collect samples from two or morearbitrarily selected 5-acre sections thatrepresent similar soil types and crophistories. There’s no need to samplethe entire field for detection purposes.For individual plants, collect samplesfrom the drip line of the plant, anglingdiagonally down into the root zone.

Q. How should soil samples becollected?

A. You’ll need the following items: asoil coring tube (you can use any soilsampling device such as a trowel orshovel if a soil coring tube is notavailable); a bucket; sandwich-size,resealable plastic bags, one for eachsample; a permanent marker; and acooler. Collect about 20 soil cores (orscoops) from the sample area to adepth of 8 to 10 inches (see the previ-ous paragraph for a description). Puteach core into the bucket, and mix thecores thoroughly after all cores havebeen collected. Remove enough of themixed sample to fill a plastic bag. Sealthe bag and mark it with the perma-nent marker so that you’ll know wherethe sample came from when the re-

sults come back. Place the sample inthe cooler and keep it cool until youcan pack it and ship it to a lab foranalysis. Allowing the samples to heatup will effectively cook the nematodesin the soil and make it impossible foryou to get a good analysis. If you’regoing to keep the samples for morethan a day, put them in a refrigerator.

Q. Why should you sample in thespring?

A. Although it’s true that the PPNpopulations will be highest in the fall,the damage they do depends on thenumber present in the spring whenroot growth begins. We can betterpredict the possibility of PPN injury ifwe know which ones and how manyare present at the beginning of thegrowing season. You can, of course,take a sample any time. Once PPNsare established in a field, they’re notgoing to go away. But they can bemanaged in most situations, if youknow what and how many they are.We can help!

Q. Where should you send the sam-ples for analysis?

A. Illinois has a number of soil testinglabs that can do nematode analyses,especially for the soybean cyst nema-tode. The University of Illinois PlantClinic can provide nematode analysesfor any crop or home landscape plant(see http://www.cropsci.uiuc.edu/research/clinic/spe_frames.html).

For further information, call TerryNiblack at (217)244-5940 or e-mailtniblack@uiuc.edu.—Terry Niblack

The Conditions Are Right forFoliar Diseases of Alfalfa inIllinois

The recent wet and cool weather inIllinois, along with frost in parts of thestate, following a period of rapidgrowth of alfalfa, is creating favorableconditions for foliar diseases. Alfalfafoliar diseases are often common atthis time of the year, especially in thelower part of the plant. Spring black

PLANT DISEASES

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stem and leaf spot was recently re-ported by Matt Montgomery of theSangamon/Menard Extension unit.This disease is common in Illinois.Omar Koester, from the Monroe/Randolph Extension offices, reportsmajor problems with alfalfa weevil butminimal problems with alfalfa foliardiseases. However, foliar diseases candevelop quickly during favorableconditions.

Many of the foliar diseases appearsimilar at first look (i.e., as smallbrown spots, but they often can bedistinguished with a closer look). Afew scattered spots on the leaves andstems are not something to be con-cerned about, but these diseases candevelop to the point where they causesevere defoliation, leading to yieldloss, reduced quality, and plant stress.The fungi that cause most foliar dis-eases overwinter on old leaves andstems, then produce spores in thespring that spread to the new growth.Here is a short summary of somecommon fungal leaf spot diseases ofalfalfa.

Spring leaf spot and black stem(caused by the fungus Phomamedicaginis) is a very common dis-ease at this time of the year (and in thefall). This disease often starts on thelower leaves, petioles, and stems andmoves upward. Dark brown to blackspots develop and may form into largespots. Lesions on the stems can be-come severe and may girdle the stems.This disease can cause defoliationwhen weather is cool and wet, and isusually most severe in the lower partof the canopy. Phoma is also one ofseveral different pathogens that cancause crown and root rot.

Lepto leaf spot (sometimes called“pepper spot”) can also occur at thistime of the year and can be a problemthroughout cool, wet summers. Symp-toms of Lepto leaf spot (caused by thefungus Leptosphaerulina briosiana)are light brown spots, about 1/32 inchor slightly larger on leaflets, and oftenare surrounded by chlorotic halos.

When this disease is severe, it cancause severe defoliation.

Common leaf spot may also be wide-spread in parts of Illinois throughoutthe summer. Like most foliar diseases,it doesn’t kill plants but can causedefoliation. This disease (caused bythe fungus Pseudopeziza medicaginis)causes small brown spots, about 1/32inch in diameter, that usually remainas separate lesions without a chlorotichalo. It usually starts on the lowerfoliage and moves up the plant, and ismore severe after the first cutting ofthe season.

Although the name is similar, thedisease “summer” leaf spot and blackstem is distinctly different from“spring” leaf spot and black stem.Summer leaf spot and black stemusually is not seen on the first cuttingand begins later on the second andfollowing cuttings. It is caused by thefungus Cercospora medicaginis. Le-sions on leaves and stems are typicallychocolate brown at first and often arefairly large (1/8 to 1/4 inch in diam-eter). The lesions develop and turn to asilvery tint and often have a yellowhalo around them.

Management of foliar diseases ofalfalfa is based primarily on cutting toreduce yield and quality losses due todefoliation. Stands should be har-vested as soon as possible if foliardiseases are severe, even if it is beforethe optimal harvest time based on thegrowth stage of the alfalfa. Goodmanagement and fertilization (espe-cially potassium) practices may alsohelp to reduce losses from foliar dis-eases. Choose well-adapted, high-yielding alfalfa varieties. Unfortu-nately there are no alfalfa cultivarsavailable with high levels of resistanceto foliar diseases; however, many ofthe new cultivars suffer less damagefrom these diseases than older variet-ies.—Dean Malvick

Weeds on the Horizon

This past winter, at Extension meet-ings throughout the state, we con-ducted a survey titled “The IllinoisInvasive Weeds Survey.” This surveywas designed to determine what weedsare thought to be the most prevalentthroughout the state and to give us ahead start on what may be some of theemerging weed problems in the future.It has been a number of years since asurvey of this nature has been con-ducted in Illinois, and it is very inter-esting to look back and compare theresults from past years.

The first question of the survey askedthe participants to rank the top sixweed species that they encounteredmost frequently in their cornfields andsoybean fields. This question gener-ated a list of 76 different species incorn and 68 different species in soy-beans. Not surprisingly, waterhemp,giant foxtail, and giant ragweed wereamong the top three weeds that wereranked as the number one most com-mon in both corn and soybeans. Theseresults are very different comparedwith results from a survey conductedin 1995 that ranked velvetleaf, com-mon cocklebur, and giant ragweed asthe most common weeds in corn andvelvetleaf, common lambsquarters,common cocklebur, and giant ragweedas the most common weeds in soy-beans. Table 1 lists the weeds thatgrowers, retailers, consultants, andExtension educators ranked as the topsix broadleaf weeds in corn and soy-beans. This table also provides per-centages of how many times that weedappeared as the number one mostcommon weed on the survey. In thissurvey, annual grasses as a group wereranked number one in corn and num-ber two in soybeans. More than 50%of the annual grass weeds were ac-counted for by foxtail species, fol-lowed by fall panicum, shattercane,and woolly cupgrass (Table 2).

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The next question asked the partici-pants to rank the top three weed es-capes that they most frequently en-counter in their cornfields and soybeanfields, and whether they were escapesdue to “late emergence” or “hard tocontrol.” The top three escapes in cornwere ragweed, waterhemp, and giantfoxtail; in soybeans, waterhemptopped the list, followed by giantragweed, with velvetleaf and commonlambsquarters tying for third (Table 3).

The next question asked what herbi-cide-resistant weed species are beingencountered in their fields. This topicwill be covered in the next issue of theBulletin in an article reviewing herbi-cide resistance. The final questionasked what weed species are becom-ing more frequent or invasive in fields,ditches, and wooded areas. The topthree weeds that are becoming moreinvasive in fields are waterhemp, giantragweed, and common pokeweed.Even though waterhemp and giantragweed ranked extremely high in theprevious questions, many growers are

just beginning to see these weedsmove into their fields. Giant ragweed,common pokeweed, and poison hem-lock were ranked the top three weedsin ditches, and in wooded areas com-mon pokeweed, multiflora rose, andgiant ragweed topped the list. Know-ing which weeds are becoming moreprevalent in these areas should give usan idea of what the problem weeds ofthe future will be.—Christy Spragueand Aaron Hager

Weed Control Options in CornAfter the PreemergenceApplication Window

With the recent rains and forecasts ofmore to come, getting corn planted hasbeen a challenge. In many cases thismad rush to plant and the extremewinds that have been plaguing us overthe past few weeks have put us in thesituation again where it is going to bevery difficult to get soil-applied herbi-cides sprayed in a timely fashion. Thiswill leave many growers and applica-tors with the decision of what to do forweed management strategies on thoseacres that won’t be treated until thecorn crop has emerged. There areessentially two different approachesthat can be taken in this situation. Thefirst option is to use the soil-appliedherbicide program that was initiallyplanned, and the second option is toswitch to a total postemergence strat-egy.

The option of using a delayed applica-tion of a soil-applied herbicide re-quires consideration of several factors.Many, but not all, soil-applied cornherbicides can be applied after cornemergence. Keep in mind that not allof these herbicides will controlemerged weeds. Additionally, there area number of soil-applied herbicidesthat can cause significant crop injuryif they are applied after corn emer-gence. So in some instances, addi-tional management strategies mayneed to be implemented to controlexisting vegetation. These strategiescould include the use of a rotary hoe

Table 3. Top three weed escapes in corn and soybeans and whether theyare “hard to control” or missed due to “late emergence.”

Escapes in cornHard tocontrol

Lateemergence Both

1. ragweed 30% 44% 36%2. waterhemp 4% 68% 28%3. giant foxtail 34% 59% 7%

Escapes in soybeans1. waterhemp 7% 59% 34%2. ragweed 30% 38% 32%3. velvetleaf/lambsquarters 45%/61% 48%/25% 7%/14%

Table 1. Top six broadleaf weeds in corn and soybeans in Illinois.

Top six weedsin corn

Percentranked #1

Top six weedsin soybean

Percentranked #1

1. Amaranthus spp.a 32 Amaranthus spp. c 442. ragweed spp.b 31 ragweed spp. d 223. velvetleaf 18 velvetleaf 15

4. c. cocklebur 8 c. lambsquarters 45. c. lambsquarters 2 c. cocklebur 6

6. morningglory 3 morningglory/nightshade

1/2

a Not all Amaranthus species were specified; over 75% were specifically listed as waterhemp.b Type of ragweed species was not always designated; over 80% were listed as giant ragweed.c Over 80% were specifically listed as waterhemp.d Over 70% were specifically listed as giant ragweed.

Table 2. Most common annual grass species in Illinois corn andsoybean fields.

Annual grassesin corn

Percentin corn

Annual grassesin soybean

Percent insoybean

1. foxtail spp.a 54 foxtail spp. a 652. fall panicum 20 fall panicum 123. shattercane 12 woolly cupgrass 114. woolly cupgrass 10 shattercane 85. others 4 other 4

a Majority of species listed were giant foxtail.

Pest Management & Crop Development Bulletin • No. 6 / May 3, 2002

68

or the addition of a herbicide that haspostemergence activity. Table 4 con-tains information about which “tradi-tional” soil-applied corn herbicidescan be applied postemergence andsome considerations to remember ifthese herbicides are applied toemerged corn. For additional informa-tion, consult the respective productlabels.

If you are considering the option ofswitching to a total postemergenceherbicide program, there are also somepoints that should be addressed. First,there are a number of goodpostemergence corn herbicide optionsavailable to growers, and informationon these products can be found inChapter 2 of the Illinois AgriculturalPest Management Handbook. How-ever, a number of these herbicides donot provide any soil residual control,and often the timing of herbicide ap-

Table 4. Maximum corn sizes for postemergence applications of soil-applied herbicides.

HerbicideMaximum corn size forbroadcast applications Comments

Axiom Before corn emergence • Applications to emerged corn may cause injury.

Balance, Epic Before corn emergence • Applications to emerged corn will cause injury.

Define Before corn emergence • Do not apply to emerged corn.

Princep Before corn emergence • Do not apply to emerged corn.

Lasso Before corn emergence • Do not apply to emerged corn.

Hornet WDG 2 inches (soil-applied) • Hornet is also labeled for postemergence applicationsup to 20 inches (V6 ).

Micro-Tech 5 inches • Will not control emerged weeds.

Bullet 5 inches • Will provide control or partial control of small (<2 lf)broadleaf and grass weed species.

Bicep II Magnum, Bicep Lite IIMagnuma

5 inches • Will provide control or partial of small (<2 lf) broadleafgrass weed species.

Frontier, Outlookb, GuardsmanMax

12 inches • Frontier and Outlook will not control emerged weeds.

Surpass, TopNotch, FulTime,Harness, Harness Xtra, Degree,Degree Xtra

11 inches • Surpass, TopNotch, Harness, and Degree will notcontrol emerged weeds.

atrazine 12 inches • Add crop oil concentrate if weeds have emerged.

Python WDG 20 inches (V6) • Use water only as a carrier.

Callisto 30 inches (V8) • Can be applied postemergence at 3 fl oz/A.

Prowl 30 inches (V8) • Will not control emerged weeds.

Dual II Magnum up to 40 inches • Will not control emerged weeds.a Bicep II Magnum and Bicep Lite II Magnum are labeled for directed applications up to 12-inch-tall corn.b Frontier and Outlook are labeled for layby applications up to 36-inch-tall corn.

Table 5. Postemergence cornherbicides with minimum corn sizerestrictions.

HerbicideMinimumcorn size

Beacon (primisulfuron) 4 inches

Distinct (diflufenzopyr +dicamba)

4 inches

Celebrity Plus (Distinct +nicosulfuron)

4 inches

Northstar (primisulfuron +dicamba)

4 inches

Resource (flumiclorac) 2-leaf

Spirit (primisulfuron +prosulfuron)

4 inches

plication is critical for providingseason-long weed control. Anotherpoint to consider is that, while weoften stress a maximum corn height ordevelopmental stage forpostemergence herbicide applications,some postemergence corn herbicidelabels indicate a minimum size ordevelopmental stage the corn shouldbe at before an application is made.This is a particularly important consid-eration when deciding on apostemergence herbicide programwhen corn is in its early developmen-tal stages. Table 5 lists thepostemergence corn herbicides thathave minimum corn size label restric-tions. So, remember, there are a num-ber of considerations that need to bemade when deciding on weed manage-ment strategies for early-seasoncorn.—Christy Sprague and AaronHager

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Pest Management & Crop Development Bulletin • No. 6 / May 3, 2002

Corn Planting Delays

The official estimates have the Illinoiscorn crop 25% planted by April 28,compared to a 5-year average of 32%and the 2001 number of 46% plantedby this date. The United States hadabout 25% of the corn crop planted atthe end of last week, with a widerange among states; Missouri hadabout 62% planted and Iowa 33%, butIndiana had only 4% of its corn cropplanted. While these numbers are notrecord setting, this planting season isshaping up as one of the more difficultones of recent years, at least in Illinoisand states east of here.

Besides the slow progress to date,many fields are quite wet; drying rateshave been slow due to cool tempera-tures; and the planting progress hasbeen very uneven, with some areasmostly planted and others yet to start.There is clearly a lot of stress build-ing, as producers watch fronts con-tinue to march across the state, andwith the “problem” date—that afterwhich yields will decline with eachday’s delay in planting—rapidly ap-proaching. Data that we use to predicteffects of planting delays on yield infact show a slightly slower rate ofyield loss with planting date delaysthan most people think, but recentsprings have allowed timely planting,and many of us start to worry by thetime the calendar turns over to May, ifnot before. We certainly worry aboutwhen we will finish, even with a mod-est delay in when we start.

The data we use to predict plantingdelays are from research we did in thenorthern half of the state in the late1980s. Such studies are very difficult,given that we can rarely plant when-ever we want to in April and May.They can also be compromised byplanting when the soil’s not fit toplant, thus poorly representing whatproducers will do. But the work wedid went fairly well due to dry springs(1988 and 1989, which were followedby very dry summers also), and we

think the numbers are reasonablypredictive over much of Illinois. I amnot aware of similar data from studiesin southern Illinois, but I think it’sreasonable to expect similar responsesthere. Avoiding dry weather later inthe season may be more important inthose soils, but the growing degree-day accumulation is faster in May andJune, and the frost date is later, whichhelps to compensate for soil effects.It’s only an anecdote, but some of thehighest yields we have had atBrownstown were in 1993, whenplanting was in early June, but itrained all summer long.

The results of the planting date study,including information needed to makereplant decisions, are in the IllinoisAgronomy Handbook. With a fullstand, we found the following yieldsas planting was delayed:

Plantingdate Yield, % of maximum

April 30 100

May 4 99

May 9 97

May 14 95

May 19 91

May 24 86

May 29 81

Although yield loss accelerates withplanting delays, to about 1% (1 1/2bushels) per day of delay by the end ofMay, it starts more gradually, with atotal loss of only about 5% (7 to 8bushels) by mid-May. It is importantto recognize that, while these numbersmay represent average losses we canexpect, they will almost never repre-sent losses that might be experiencedwithin a given field in a given year.

Some of the variability in response toplanting date is due to continuingweather factors (for example, therecent weather has been cool withvery slow-growing degree-day accu-

mulation, meaning that the develop-ment of corn whose planting is de-layed is not falling very quickly be-hind that of planted corn, as it wouldbe if the weather were warm and cornplanted in mid-April were up andgrowing). In contrast, April 2001 wasvery warm, and late-planted corn(which in 2001 meant corn plantedlater than early May) never caught up;yields suffered as a result, especiallyin areas that had low rainfall later inthe summer. In contrast, we accumu-lated only about 247 GDD in Aprilthis year at Urbana, and more than60% of that was accumulated duringthe warm stretch from April 11 to 19,by which time very little corn hadbeen planted. Rainfall in July andAugust will, as always, be the mostimportant factor affecting yield ofcorn in Illinois. Once it warms up inMay (providing we get the cropmostly planted by then), differences indevelopment between corn planted inmid-April compared to that planted inmid-May will not be large.

Management decisions we make canand will affect how the crop respondsto delayed planting. During the rathergradual declines in yield potentialduring the first half of May, we can inmost fields do more damage by work-ing and planting when soils are toowet than we can even gain by planting3 or 4 days earlier. Of course, there isno guarantee that the weather will turnwarm and dry any time soon. But thetime to take desperate measures—suchas planting as soon as “I can getthrough without getting stuck”—iscertainly not here yet. Compactionbefore and during planting, whichmakes root growth more difficult, hasthe same practical effect as late plant-ing—it makes good yields more de-pendent on good weather later in theseason than we would like the case tobe.

In most cases, we probably wantplanting to be the first operation doneas soon as soil conditions allow, withnitrogen and herbicide applicationdone afterward so that planting is notfurther delayed. But we also need to

CROP DEVELOPMENT

Pest Management & Crop Development Bulletin • No. 6 / May 3, 2002

70

be reasonable in our approach to diffi-cult weather conditions, recognizingthat very good yields are possible evenwhen corn is planted in May.—Emerson D. Nafziger

Nitrogen Loss for 2002

The warmer-than-normal winter,coupled with a wet spring, has manywondering whether nitrogen loss is orwill be greater than normal for the2002 crop year. Fortunately, researchconducted at the University of Illinoisover a number of years has provided adata base on which to make an in-formed decision about the amount ofN loss that has occurred or that mightoccur in the next few weeks.

Nitrogen loss associated with exces-sively wet soils will occur only fromthat portion of the fertilizer that is inthe nitrate form when soils becomesaturated. Because most fertilizers areapplied as ammonium or a form thatquickly converts to ammonium, youmust first determine how much of theapplied nitrogen has been converted tonitrate. This rate of conversion ofammonium to nitrate—a processcalled nitrification—is primarily de-pendent on soil temperature. Nitrifica-tion does not occur when soils arefrozen, but it does occur at tempera-tures above freezing and is faster thewarmer soils are. Equations that de-fine the relationship between soiltemperature and nitrification havebeen developed for two Illinois soils, aDrummer silty clay loam and a Cisnesilt loam. These equations, using dailysoil temperature data provided by theIllinois State Water Survey for theDrummer at DeKalb and Bondville

and the Cisne at Brownstown wereused to estimate the amount of fall-applied nitrogen that had been con-verted to nitrate during the winter andspring of 2001–2002 (Table 6).

As expected, there were significantdifferences in the rate of nitrification,dependent on location, with highervalues the farther south in the state.Addition of a nitrification inhibitor, N-Serve, substantially reduced the rate ofconversion of ammonium to nitrate.

The conversion of ammonium to ni-trate does not mean that it has beenlost from the soil system but ratherthat it is susceptible to loss in fieldsthat have been or may become satu-rated with water for several days.When soils are excessively wet, nitro-gen will be lost through the process ofdenitrification or leaching. As of April1, the amount of nitrate–nitrogen lostfrom tile lines was less than 6% of theequivalent of the total fertilizer nitro-gen applied without a nitrificationinhibitor in a central Illinoisexperiment.

Denitrification is the major nitrogenloss mechanism in most Illinois soils,particularly in medium to heavy tex-tured soils. Illinois research hasshown that 4 to 5% of the amount ofnitrate–nitrogen present (note that thisis not 4 to 5% of the total nitrogenapplied) will be lost via denitrificationfor each day that soils are saturatedwhen soil temperature is above 65 to70ºF. At temperatures less than 55ºF, itis estimated that denitrification will becloser to 1 to 2% of the nitrogen that isin the nitrate form. Prior to April 25,soil temperatures were less than 55ºFall but 8 days in central and northern

Table 6. Rate of conversion of ammonium to nitrate during the 2001–2002 winter–spring season.

Fertilizer application

Ammonia without N-Serve Ammonia with N-Serve

Nitrification period DeKalb Bondville Brownstown DeKalb Bondville BrownstownPercent of ammonia nitrified (present as nitrate at end of period)

Nov.1–Apr.1 30 39 100 12 15 41Dec. 1–Apr. 1 14 20 61 5 8 22Apr. 1–Apr. 25 17 20 7 8 25

Illinois and 15 days in southern Illi-nois.

Assuming 7 days of saturated soils inlate April and 160 pounds of nitrogenapplied without a nitrification inhibi-tor on November 1, 2001, the losspotential would be 160 lb N/acre x59% [.59] (nitrification rate) x 19%[.19] (7 days saturated at 2% denitrifi-cation per day + 5% leaching) = 18 lbN/acre loss for a central Illinois loca-tion. If a nitrification inhibitor hadbeen used, the loss potential would bereduced to 160 x .23 x .19 = 7 lb N/acre. For a southern Illinois location,the comparable situation would be 160x 100% x .19 = 30 lb N/acre withoutan inhibitor, or 20 lb N/acre with aninhibitor.

The bottom line of this analysis is thatmost producers need not worry aboutN loss up to this time. They can savethat worry for later in the season ifsoils become saturated.

This information will be updated asthe season progresses. Additionalnitrogen is not being recommended atthis time to compensate for loss. Pro-ducers should wait until late Maywhen additional information will beavailable to better predict the need foradditional nitrogen.—Robert Hoeft

Plant, Then Sidedress

Wet soils this spring have delayedmost field activities, particularly cornplanting. Don’t delay planting to waituntil nitrogen fertilizer has been ap-plied. Plant, then sidedress.Sidedressing can start as soon as thecorn is planted, even before the corn is

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Pest Management & Crop Development Bulletin • No. 6 / May 3, 2002

REGIONAL REPORTS

up if you can see the planter tracks toensure that the nitrogen will be placedbetween the rows. There will be nodanger of ammonia burn if the mate-rial is injected between the rows. Ifyou are sidedressing, consider usinginjector knives every other row insteadof every row. Research has shown thatalternate-row nitrogen application isequally as effective as every-rowapplication. Both ammonia and urea-ammonium nitrate solutions can beapplied with the alternate-row tech-nique. For more details on the use ofalternate-row application, see theIllinois Agronomy Handbook at http://web.aces.uiuc.edu/iah/.

If you use preplant ammonia, be sureto wait at least 5 days before planting.The greatest risk of ammonia damageoccurs when ammonia is applied to awet soil that dries rapidly. Insertion ofa knife into wet soil creates a compac-tion zone along the knife track. Theammonia is then held in this zone,reducing the rate of conversion ofammonia to ammonium. When soilsdry, the ammonia moves up the crackthat is formed along the injection knifetrack. If the corn row is directly overthe knife track, ammonia damage willoccur.—Robert Hoeft

Extension center educators, unit edu-cators, and unit assistants in northern,west-central, east-central, and south-ern Illinois prepare regional reports toprovide more localized insight intopest situations and crop conditions inIllinois. The reports will keep you upto date on situations in field and for-age crops as they develop throughoutthe season. The regions have beendefined broadly to include the agricul-tural statistics districts as designatedby the Illinois Agricultural StatisticsService, with slight modifications:

• North (Northwest and Northeastdistricts, plus Stark and Marshallcounties)

• West central (West and West South-west districts, and Peoria,

Woodford, Tazewell, Mason,Menard, and Logan counties fromthe Central district)

• East central (East and East South-east districts [except Marion, Clay,Richland, and Lawrence counties],McLean, DeWitt, and Macon coun-ties from the Central district)

• South (Southwest and Southeastdistricts, and Marion, Clay,Richland, and Lawrence countiesfrom the East Southeast district)

We hope these reports will provideadditional benefits for staying currentas the season progresses.

Northern Illinois

Field activity was very limited duringthe past week, as most of northernIllinois received rainfall on April 24and 27. Total precipitation rangedfrom 0.5 inch to 1.5 inches. Some cornplanting did occur but on a limitedbasis. Generally over the past fewweeks as fields approached being dryenough to plant, another storm frontentered the area. There have been afew reports of corn emergence, butvery few reports north of Interstate 80.

Black cutworm moths were caught ina trap located in Lee County, but todate there have been no reports of anintense moth capture.

West-Central Illinois

Wet soil conditions continue to existthroughout the region, with little, ifany, planting this past week. Sinceweather and soil conditions are notpromising for the next few days, plant-ing will likely be delayed even more.

Many cornfields planted the week ofApril 15 are emerged, with seeminglygood populations, except for theponded areas. Those spots will beevaluated when it dries up, with re-planting a definite possibility. A lightgreen to yellow plant color indicates anutrient availability problem at thistime. That condition will probablyimprove as soon as growing condi-tions become more ideal.

No pest problems have been reportedin corn at this time.

Alfalfa weevils are a major problem inmost fields. Fields in the southern partof the region are well beyond thethreshold levels of three or more perstem and 25% plant skeletonization.Insecticide applications are beingmade in those fields; be sure to checkfor the preharvest interval when usingany insecticide.

Wheat fields have progressed rapidly,with many fields in the GS 8 stage andflag leaf visible. So far this is littleevidence of disease, but that couldchange quickly if wet weather contin-ues.

Fields with fall-applied herbicideshave remained fairly weed free, whileothers with no herbicide are greeningup and will probably require moretillage when it dries up.

Contributing Authors

Aaron Hager (hager@uiuc.edu),Extension Weed Science, (217)333-4424

Robert G. Hoeft(hoeftr@mail.aces.uiuc.edu), CropSciences, (217)333-4424

Dean Malvick (dmalvick@uiuc.edu),Extension Plant Pathology, (217)265-5166

Jim Morrison(morrisonja@mail.aces.uiuc.edu),Extension Crop Systems, (815)397-7714

Emerson Nafziger (ednaf@uiuc.edu),Crop Sciences, (217)333-4424

Terry Niblack(tniblack@staff.uiuc.edu), Crop Sci-ences, (217)244-5940

Christy Sprague(lsprague@staff.uiuc.edu), ExtensionWeed Science, (217)333-4424

Kevin Steffey (ksteffey@uiuc.edu),Extension Entomology, (217)333-6652

Pest Management & Crop Development Bulletin • No. 6 / May 3, 2002

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