Pest&Crop No. 4 April 29, 2011 • Page 1

Purdue Cooperative Extension Service April 29, 2011 - Issue 4

http://extension.entm.purdue.edu/pestcrop/index.html

I n T h i s I s s u e

Insects, Mites, and Nematodes • BlackCutwormFindingHoosierHospitality • AccumulatedHeatUnitsforAlfalfaWeevil

• BlackLightTrapCatchReport • BlackCutwormAdultPheromoneTrapReport

Weeds • PoisonHemlockControlinCornandSoybean • ColdWetWeatherandPostemergence,SpikeStage

HerbicideApplicationsinCorn

Plant Diseases • RidomilGoldSLApprovedforUseinTobaccoTrans-

plantWaterinIndiana

• MonitortheRiskofFusariumHeadBlight(Scab)inIndianaWheat

Agronomy Tips • TillageConsiderationsforDelayedPlantingofCorn

inaWetSpring

• “Safe”HybridMaturitiesforDelayedCornPlantinginIndiana

• ThoughtsonSeedingRatesforCorn

Weather Update • TemperatureAccumulations

I n s e c t s , M i t e s , A n d N e m a t o d e s

Black Cutworm Finding Hoosier Hospitality-(Chris-tian Krupke and John Obermeyer)

•Blackcutwormmotharrivalhasneverbeenhigher.•Mothsareseekingweedyfieldstolaytheireggs,plentytochoosefrom.

•Seedinsecticidesandtraited-cornmaybelittlehelpifcool,wetconditionspersistafterplanting

Lookat thisweek’s “BlackCutwormAdultPheromoneTrapReport.”Ourdutifulcooperatorshavecapturedaninor-dinatenumberofmothstheselastcoupleweeks.AsofApril15,we’vebeguntrackingheatunitaccumulationstopredictfuturecuttingbythispest,developmentalmappublishedinfutureissuesofthePest&Crop.

Thekeyquestionis:willegg-ladenblackcutwormmothsarrivinginourfairHoosierstatefindyourfieldsattractiveto

Cityfolksthinkthesefieldsarepretty...sodoblackcut-worm!

Pest&Crop No. 4 April 29, 2011 • Page 2

layeggsin?Therearesomecluesthathelpgiveusanan-swer:Barrenfieldsarenotappealing.Mothsareparticularlyattracted towinter annuals, such as chickweed andmus-tards.But theblackcutwormhasabroadhostrange,andfields thatareshowingplentyofgreen,yellow,andpurple(henbit) areathighest risk for cutwormdamage.Remem-ber,cornisoneoftheblackcutwormsleastfavoritefoods,itjustsohappensitistheonlyplantremainingbythetimelarvaehaveemergedandweedshavebeenkilled.Cutwormlarvaestarve ifweedsare treatedwith tillageorherbicide2-3weeksbeforecornemergence.Itisobviouslytoolateforthatthisyear.

Wedon’twantproducers tohavea falsesenseofse-curitywithseed-applied insecticidesandsomevarietiesofBt-traitedcorn,wherethelabelprovidesonly“suppression”andnot“control”. Checkthefineprintonthetraityouareusing!Suppressionisfineunderidealenvironmentalcondi-tionsandmoderateinfestationlevels.Thesystemicactivityoftheseed-appliedinsecticide,and/ortheproteinproductionoftheBt-cornareoptimalwhenthecornseedlingisactivelygrowing.However,underenvironmentalstress(i.e.,yellowcorn,coldandwetsoil)theefficacyofthesecontrolproductsaregreatlyreduced,leavingthestrugglingseedlingvulner-

abletoattackbyaboveandbelowgroundinsectpests.Wewillcontinuetoupdateincomingweeksandincludescout-ingandtreatmentguidelinesinfuturearticles.Fornow,wewillwaitandsee–withonly2-5%ofthecornplantedinthestate,itwillbesometimebeforeweseedamage.

Blackcutwormeggscomparedtopenny’sLincolnhead

Bug Scout says “Hey central and southern Indiana, don’t forget alfalfa weevil scouting!”

Pest&Crop No. 4 April 29, 2011 • Page 3

Black Light Trap Catch Report - (John Obermeyer)

County/Cooperator

4/19/11 - 4/25/11

VC BCW ECB SWCB CEW FAW AW VC BCW ECB SWCB CEW FAW AW

Dubois/SIPACAgCenter 0 0 0 0 0 0 0

Jennings/SEPACAgCenter 0 0 0 0 0 0 7

Knox/SWPACAgCenter 0 0 0 0 0 0 0

LaPorte/PinneyAgCenter 0 2 0 0 0 0 14

Lawrence/FeldunAgCenter 0 4 0 0 0 0 8

Randolph/DavisAgCenter 0 2 0 0 0 0 18

Tippecanoe/TPACAgCenter 0 4 0 0 0 0 21

Whitley/NEPACAgCenter 0 4 0 0 0 0 32

VC=VariegatedCutworm,BCW=BlackCutworm,ECB=EuropeanCornBorer,SWCB=SouthwesternCornBorer,CEW=CornEarworm,FAW=FallArmyworm,AW=Armyworm

Black Cutworm Adult Pheromone Trap ReportWeek 1 = 4/14/11 - 4/20/11 Week 2 = 4/21/11 - 4/27/11

County Cooperator

BCW Trapped

County Cooperator

BCW Trapped

Wk 1 Wk 2 Wk 1 Wk 2

Adams Kaminsky/ New Era Ag 21* 0 Jennings Bauerle/SEPAC 3 0

Adams Roe/Mercer Landmark 47* 18 Knox Bower/Ceres Solutions/Oaktown 17 20

Allen Anderson/Syngenta Seed 7 Knox Bower/Ceres Solutions/Vincennes 46* 7

Allen Gynn/Southwind Farms 24* 1 Knox Bower/Ceres Solutions/Frichton 0 2

Allen Hoffman/ATA Solutions 5 20* Knox Hoke/SWPAC 4 0

Benton Babcock/Ceres Solutions 28* 10* Lake Kleine/Kleine Farms 32* 75*

Clay Bower/Ceres Solutions - Brazil 6 4 Newton Ritter/Purdue CES 16 1

Clay Bower/Ceres Solutions - Clay City 1 2 Porter Leuck/PPAC 26 16

Clinton Foster/Purdue Entomology 38* 4 Putnam Nicholson/Nicholson Consulting 8 1

Dubois Eck/Debois Co. Purdue CES 7 1 Randolph Boyer/DPAC 6 0

Elkhart Willard/Crop Tech Inc. 14 14* Rush Schelle/Falmouth Farm Supply 15 0

Fayette Schelle/Falmouth Farm Supply 16* 1 Starke Wickert/Wickert Agronomy Services 3 0

Fountain Mroczkiewicz/Syngenta 11 12 Sullivan Bower/Ceres Solutions - Sullivan W 1 0

Fulton Jenkins/N. Central Coop - Kewanna 40* 18* Sullivan Bower/Ceres Solutions - Sullivan E 2 6

Fulton Jenkins/N. Central Coop - Rochester 14* 13* Tippecanoe Bower/Ceres Solutions - West Point 7 5

Hamilton Beamer/Beck’s Hybrids - Atlanta 21 11 Tippecanoe Nagel/Ceres Solutions 42* 31*

Hamilton Beamer/Beck’s Hybrids - Sheridan 18 0 Tippecanoe Obermeyer/Purdue Entomology 12 2

Hendricks Nicholson/Nicholson Consulting 49* 2 White Reynolds/ConAgra Snack Foods 10* 0

Henry Schelle/Falmouth Farm Supply 7 1 Whitley Walker/NEPAC 34* 1

Jasper Overstreet/Purdue CES 8 2

Jay Shrack/RanDel AgriServices 18* 0

*=Intensive Capture...this occurs when 9 or more moths are caught over a 2-night period

Pest&Crop No. 4 April 29, 2011 • Page 4

W e e d s

Poison Hemlock Control in Corn and Soybean –(Glenn Nice)

AlthoughPoisonhemlockhasbeentroublesomeinpas-turesandrangelandforquitesometime,ithastypicallysatbeyondthebordersofcornandsoybeanfields,beingcon-tenttowatchfromrailwaytracksandtheditch.Thismaynolongerbethecase.Theadoptionofno-tillhaspromotedaweedshiftfavoringsomeoftheperennialsandbiennials.BillandIreceivecallsregardingcontrolofhemlockinrowcrops,particularlyinsoybean.Mostoftengrowersandapplicatorswereconcernedthatglyphosatealonejustpriortoplantingorasthe1stpostemergencespraydidnotprovideadequatecontrol.Wenoticedthatpoisonhemlockisactivelygrowinginditchbanksandalongfieldedges.Sothepurposeofthisarticleistoprovidesomeguidanceonhowtomanagethisweed.

Poisonhemlockisabiennial,meaningthatittakestwoyearsforittocompleteitslifecycle.Thefirstyearitexistsasalowlyingrosette(Figure1.),thenitwillboltafteroverwin-teringandbethreetoeightfeettallatmaturity.Poisonhem-lockflowersinJuneorJulyandonceseedisproducedgen-erallydieslateJulyandAugust.Wegenerallyreceivecallsregardingthecontrolofpoisonhemlockwhenithasreachedmaturityandisfloweringout.Biennialsareoftenmoresus-ceptibletochemicalcontrolinthefirstyearofgrowthwhentheyarerosettes.

Poisonhemlockrosettesinthespring.

Control

Poisonhemlockhistoricallyhasnotbeenaproblemincornandsoybean.Becauseofthisthereisnotalargebodyof researchdoneonpoisonhemlock’scontrol incornandsoybean. Ifyouhavepoisonhemlock inyourno-tillfield itisagoodideatoaddeitherdicambaor2,4-Dinyourburn-downsandtotargetpoisonhemlockinthefirstyearsgrowth,whileitisstillarosette.Belowaresomeoftheoptionsavail-

abletosuppressorcontrolpoisonhemlockincornandsoy-beansituations.

Corn and Soybean

Burndown applications of glyphosate plus 2,4-D (1 lbai/A)inthefallcancontrolrosettesinthefallorintheearlyspring.Applicationsof2,4-Dofrateshigherthan0.5lbai/Arequire a 30 dayswaiting period before planting soybeanand 7 to 14 days before planting corn (see specific labelfordetails).Glyphosatelabelsrecommendapplicationsfrombudtoflower.

GlyphosatecanalsobeusedPOSTinRRsoybeanandcorn.

Corn

BurndownorPREapplicationsofBasis(0.5oz/A)plus2,4-DLVE(1pt/A)orBasis(0.3to0.5oz/A)plus2,4-D(1pt/A)plusatrazineat0.5to1lbai/A.Thereisa7to14dayplanting restrictionwhenusing2,4-D toplantingcorn,seespecificproduct label for details. Basiswill provide someresidualcontrolofgerminatingpoisonhemlock.

BurndownorPOSTapplicationsofdicamba (0.5pt/A)or2,4-Dcansuppresstocontrolpoisonhemlock.Dicambaprovidesgoodcontrolwhere2,4-Dcanprovidefaircontrol.Dicambacanbeappliedbeforeplantingandpostemergencefromspiketo36inchtallcornoruntil15daysbeforetasselemergence.Risksofinjuryincreasesaftercorniseightinch-estall,theuseofdropnozzlesaresuggested.Dropnozzlesshouldbeusedwhenapplying2,4-D(0.17to0.25 lbai/A)afterthecorniseightinchestallforaddedsafety.

Soybean

Burndown applications of glyphosate (1 lb ae/A) plus2,4-D(1lbai/A)etherinthefallorearlyspringonrosettesofcanprovidegoodcontrolofpoisonhemlock.Thereisa7daywaitingperiodafter2,4-Dapplicationsof0.5lbai/Aorless,buta30daywaitingperiodwithapplicationsabove0.5lbai/Atoplantsoybean.GlyphosatecanbeusedPOSTinRRsoybean.

Cold Wet Weather and Postemergence, Spike Stage Herbicide Applications in Corn–(Bill Johnson, Glenn Nice, Purdue University, and Mark Loux, The Ohio State University)

Even though a lot of cornwas planted inmid-April, itis likely that recent rainyconditionsprohibitedmanyfieldsfromreceivingsoilappliedherbicides.Sincealmostallsoilapplied chloroacetamide/atrazine premix products can be

Pest&Crop No. 4 April 29, 2011 • Page 5

appliedtoemergedcorn, itwillbetemptingtospraythesefieldsassoonastheyaredryenoughtodriveacross.Hereareafewimportantpointstokeepinmind.

1.Cool, cloudy weather and wet soils slowthe corn plants ability to metabolize(detoxify)herbicides.Cornwillbestressedaftercom-ingthroughthecool,wetperiodandwillbemoresus-ceptibletoshowingherbicideinjurysymptoms.Thisisatypicalconditionunderwhichweseeatrazineinjuryandchloroacetamideinjury.

2.Asageneralrule,donotapplychloroacetamide:atrazinepremixesinnitrogensolutionsifthecornisemerged.Nitrogensolutionsareeffectiveinpromotingherbicideuptakeandcausingnecrosisonleavesbythemselves,resultinginsevereinjury.Mostlabelsstatethatatrazinepremixesshouldonlybeapplied inwater if thecornhasemerged.Afewproductsdoallowpostemergenceapplicationsinnitrogensolutions,butconsultthelabelifyouhavequestionsaboutaspecificproduct.

3.Anothergeneralconsiderationinvolvestankmixturesof2,4-Dwithachloroacetamide:atrazinepremixandapplyingthismixturetoemergedcorn.Theacetochlor(Harness, Degree, TopNotch, Surpass, ConfidenceandVolley)labelsindicatethat2,4-Dshouldnotbeap-pliedwithin7-14daysbeforeor3-5daysafterplanting,butbeforecropemergence.Thisrestrictioniswrittenintotothelabelbecauseofcropinjuryconcerns.Appli-cationswithin7-14daysbeforeplantingcaninjurecornbybeingwasheddownintothecornseedgerminationzone (seed furrow). Applications after corn plantingcancauseinjuryifthecombinationofproductscomesinto contactwith corn foliage. If in doubt about cropinjurypotentialofaspecificchloroacetamide:atrazinepremix,consult the label tosee if it isallowedordonottankmix2,4-Dwithatrazinepremixesandapplytoemergedcorn.

4.Ifthefieldhasadenseinfestationofemergedweedsandanaggressiveadjuvantsystemwillbeneededtoincreasepostemergenceherbicideactivity,waitafewdaystoallowthecorntorecoverfromthecoldstressbeforeapplyingherbicides.

5.Treatments that contain atrazine will control manysmall, emerged broadleaf weeds. Among preemer-genceherbicides,Lexar/LumaxandmixturesofSure-Start plusatrazineprovide thebroadest spectrumofbroadleafweedcontrol,especiallyasweedsgetlarger.Emergedgrassweedstendtobemoreofanissue.At-razinehasactivityonemergedgrasses,anditismosteffectivewhenappliedathighratestoverysmall(lessthanone inch)grasses.Productswhichcontain rim-sulfuron(Resolve)willprovidesomefoliarandresid-ualcontrolofgrassweedsandResolvecanbemixedwith either the atrazine premixes or with glyphosateorglufosinateinRoundupReadyorLibertyLinkcorn,respectively. Larger grasseswill require the additionofpostemergenceherbicidessuchasOption,Equip,Steadfast,Accent,glyphosate(RoundupReadycorn)orglufosinate (LibertyLinkcorn). ImpactandLaudisalsohavesomeactivityonemergedgrassesandtheyalsocontrolmanybroadleafweeds.However,wefeelthattheywouldfitbestinsituationsweregrassdensi-ties are low since they are not quite as effective asthepreviouslymentionedgrassherbicides.ImpactandLaudisshouldbemixedwithatrazineformosteffectivecontrol.

Thereare several cornproducts that haveboth someburndowncapabilityandcanbeappliedpostearly.Foralistofproductsandratesseetablebelow.

Table 1. Corn residual products that can be applied to young emerged corn

Herbicide Timing on Corn Rate Range[1] Comment

Harness,TopNotch,Sur-pass, Degree,ConfidenceandVolley[acetochlor]

Upto11inches Degree(3.8L)-1.25to2.75pts/ASurpass,Volley(6.4EC)-2to3pts/A

ExceptforDegree,theotherproductsmustbeappliedinwaterafteremergence.Willrequiretank-mixpartner(glyphosateinRRcornorIgniteinLLcornoratrazine)forburndownactivity.Willhavepreemergenceactivityonannualgrasses,nightshadeandpigweeds.

Harness Xtra,Degree Xtra,Fultime,Keystone,Confi-dence XtraandVolley ATZ[acetochlor+atrazine]

Upto11inchesor5to6-leaf

DegreeXtra(4L)-2.9to3.7qts/AFultime(4L)-2.25to5qts/AHarnessXtra,ConfidenceXtra(5.6L)-1.4to2.75qts/Keystone,Vol-leyATZ(5.25L)-2.2to3.4qts/A

DegreeXtraandFultimecanpro-videslightlylongerresidualcon-trol.Canprovidesomeburndowncontrolofsmallweeds(2-leaf).ExceptforDegreeXtrausewaterasthecarrierforpostemergencetreatments.Tankmixingaburn-downproductisrecommended.BalanceFlexxcanimprovecontrolofsomeweeds.

Pest&Crop No. 4 April 29, 2011 • Page 6

Table1.(Con’t)

Herbicide TimingonCorn RateRanger[1] Comment

Micro-Tech,Lasso andoth-ers[alachlor]

Upto5inches Lasso(4EC)-2to3.25qts/A

Willhavesomecontrolofseedlingweedsthatare2-leaforsmaller.Donotapplyinfertilizerwhenairtemperatureexceeds85degrees.

LariatorBullet[alachlor+atrazine]

Upto5inches Lariat,Bullet-2.5to4.5qts/A

ApplyLariatinwateronlyandBulletcanbeappliedwateror28%iftemperaturesarebelow85degrees.

Balance Flexx[isoxaflutole+cyprosulfamide(Safener)]

Upto2-leaf 3to6floz/A Donottankmixwithadjuvantsorherbicidesotherthanatrazoneonemergedcorn.Cancontrolverysmallweeds(1-leaf).

Callisto[mesotrione] Earlypostemergenceto30inchesor8-leaf

3floz/A Hasburndownactivityonbroad-leaves,butlittleresidualactivityonthepostemergencerate.

Corvus[isoxaflutole+cyprosulfamide+thiencar-bazone-methy]

Upto2-leaf 3.33to5.6oz/A Willcontrolsmallemergedweeds.Mixingwithatrazinewillincreasecontrol.Donotapplywithadju-vantsonemergedcorn.

Guardsman Max[dimethe-namid-P+atrazine]

Upto12inches 2.5to4.6pts/A Donotuseliquidfertilizerasthespraycarrier.Canbeappliedwithsurfactantorlowratesofliquidnitrogen.COCmaybeincluded.

Lexar[s-metolachlor+me-sotrione+atrazine]

Upto12inches 3to3.5qts/A Donotapplywithotherbleachersinthisclassofherbicides.Seela-belforinsecticideinteractions.Donotusewithliquidfertilizer.

Bicep II Magnum,Cinch ATZandStalwart[meto-lachlorors-metolachlor+atrazine]

Upto5inches 1.3to2.58qts/A Willcontrolsmallweeds(2-leaf).

[1]Mostproductraterangesaredependentonsoiltextureandpercentorganicmatter.

P l a n t D i s e a s e s

Ridomil Gold SL Approved for Use in Tobacco Trans-plant Water in Indiana–(Kiersten Wise)

Indiana tobacco producers have been granted a spe-ciallocalneedslabel,knownasa24(c)label,tocontrolthediseaseblack shank (Phytophthora nicotianae) in tobaccotransplantwater.ThefungicideRidomilGoldSL(mefanox-am;SyngentaCropProtection) isawater-solubleformula-tionthatcanbeappliedatarateof4to8floz/A,in200gal/Aoftransplantwater.Toavoidseedlinginjury,donotapplytheproductinlessthan200gallonsofwater/A,anddonotap-plytostressedseedlings,orduringhotanddryconditions.RidomilGoldSLisadifferentformulationthanRidomilGoldECandRidomilGold2EC.Theseformulations,orgenericversionsofmefanoxam,mayinjuretobaccoseedlingsifap-

plied inwater. Thisapplicationdoescount toward the1.5lba.i./A, or3pts/A, limit ofmefanoxamproducts that canbeapplied to tobacco inasingleseason.Producersmusthaveacopyof theIndiana24(c)special localneeds labelintheirpossessionatthetimeofthefungicideapplication.Formoreinformationonmanagingblackshankoftobacco,pleaserefertothenewsletterarticlewrittenbyKennySee-boldoftheUniversityofKentucky:<http://www.ca.uky.edu/agcollege/plantpathology/extension/KPN%20Site%20Files/kpn_11/pn_110329.html>.

Pest&Crop No. 4 April 29, 2011 • Page 7

Monitor the Risk of Fusarium Head Blight (Scab) in Indiana Wheat –(Kiersten Wise)

• Monitor thewheat scab riskmap during head emer-genceandflowering:<http://www.wheatscab.psu.edu/>

• Signupforupdatesonriskofscabat<http://scabusa.org/fhb_alert.php>.

Wheat isapproachingheademergence (Feekes10.5)infarsouthernIndiana,andisinearlyboot(Feekes10)insouthern Indiana.Wheat innorthern Indiana is furtherbe-hind,andinsomeareasisjustnowjointing(Feekes6).Aswheat approaches flowering (Feekes 10.5.1, Figure 1), insouthernIndiana,itisimportanttoconsidertheriskforFu-sariumheadblight,orscab,development.

Figure1.Feekes10.5.1,orbeginningflowering

Thefungusthatcausesheadscab,Fusarium graminear-

ium, infects wheat during flowering, beginning at Feekes10.5.1.Symptomsincludebleachedspikeletsonthehead(Figure2),andsmallorshriveledgrainkernels,commonlycalled“tombstones.”Thefungusalsoproducesmycotoxins,suchasdeoxynivalenol,orDON,whichcanaccumulateintheinfectedgrain.

Rainy,warm,andhumidweatherconditions favordis-ease development. The recent rainsmay have triggeredsporeproduction,and if thewet,humidweathercontinuesasthemajorityofwheat insouthernINbeginstoflower, itispossiblethatafungicideapplicationwillbenecessarytosuppressFusariumheadblight.

Figure2.ThebleachedspikeletspresentonthewheatheadisdiagnosticofFusariumheadblight.

Nowisagoodtimetobecomefamiliarwiththeriskas-sessmenttoolavailabletoassesstheriskofFusariumheadblightinIndiana.Thismodelcanbeaccessedthroughthefollowinglink:<http://www.wheatscab.psu.edu/>.

Atthissitethereareseverallinksthatexplainhowthemodelwasdeveloped,and linksprovidingadditional infor-mation about Fusarium head blight onwheat. To accessthemodel, click on the linkmarked “RiskMapTool.” Thefirstscreenwillexplainhowtousethemodel.Thismodelrequires that you know the approximate flowering date ofyourwheatvariety,andafterreadingtheinitialscreen,clickoncalendartoinputthedatethatyourvarietyisexpectedtoflower.Next,clickonthestatemapofIndiana.CommentaryonIndianawheatdevelopmentanddiseaseriskwillbedis-playedonthisscreen,aswellasIndianaweatherstations.ClickingonaweatherstationwithinthestatewillgenerateapredictionfortheriskofFusariumheadblightdevelopmentinthatarea(Figure3).

Thismodelusesweatherinformationincludingtempera-ture,rainfall,andrelativehumiditytocalculaterisklevelsforFusariumheadblight.Althoughitisagoodtoolforpredict-ingrisk,ithasanestimatedaccuracylevelof80%.Keepinmindthatthemodeldoesnotprovideaguaranteedpredic-tionforwhetherornotscabwilloccurinindividualfields,andadditional factorssuchas the localweather forecast,cropconditions, and Extension commentary should be consid-eredwhenassessingthelevelofrisk.Producerscansignupforalerts,courtesyoftheU.S.WheatandBarleyScabInita-tive.Alertscanbesenttoacellphoneoremail,andwillbesentoutastheriskmapupdatesriskofscabinIndiana.Tosignupforalerts,visit:<http://scabusa.org/fhb_alert.php>.

Pest&Crop No. 4 April 29, 2011 • Page 8

CroprotationandselectionofpartiallyresistantvarietiescanhelpreducetheimpactofFusariumheadblightdevel-opment,buttimelyfungicideapplicationsmaybeneededtosuppress thedisease in-season. Thereareseveral fungi-cidesavailableforFusariumheadblightcontrol,andthesearelistedinthefoliarfungicideefficacytabledevelopedbytheNorthCentralRegionalCommitteeonManagementofSmall Grain Diseases or NCERA-184 committee: <http://www.ppdl.purdue.edu/ppdl/wise/NCERA_184_Wheat_fun-gicide_chart_2010_v2.pdf>.Applicationsof fungicideprior toheademergence,suchasthoseappliedatjointingorflagleafemergencemaynotreduceFHBinfection.Besuretofollow label restrictionsonhowmanydaysmustpassbe-tweenfungicideapplicationandharvest.

Figure3.IndianacommentaryandriskofFusariumheadblightdevelopmentonthewheatscabriskmodel:<http://

www.wheatscab.psu.edu/>.

A g r o n o m y T i p s

Tillage Considerations for Delayed Planting of Corn in a Wet Spring –(Tony J. Vyn)

Introduction:

Just2%ofcornwasplanted in IndianaasofApril24,2011(USDA-NASS).Mostotherlarge-acreagecornstateswere in the same situation, and nationally only 9%of theintendedcorncrophasbeenseeded.HeavyrainsovertheEasterweekendandsincehavevirtuallyassuredthatIndi-anacornplantingisgoingtobedelayeduntilMay2attheearliest.Whensoilconditionsdofinallybecomedryenoughtosupporttractorsandotherfieldequipment,Indianafarm-erswill facepossibly different tillageandplanting choicesthantheywouldhavefacedasrecentlyaslastspring(April,2010)when they had the luxury of a prolonged period ofwarmanddryweatherconditions. Thecombinationof re-cordcornpricesandplantingdelaysunderstandably fuelsfarmeranxiety,butitalsoenhancesthefinancialimplicationsofmanagementchoicesmadeinthecropestablishmentpe-riod.Sothemajorquestionthisseasonis“Howshouldmyintendedtillageprogramchangeinresponsetothecurrentrealitiesofsaturatedsoils(ifnotoutrightponds)withinfields,the weather forecast, and the calendar?” The followingguidelinesmaybehelpfultothedecisionmakingprocess.

Tillage Considerations and Associated Recommenda-tions:

1. Maintainingtillageoptionsinspecificfieldsdependsonachievingsatisfactoryweedcontrol.Asairtemperaturesgradually warm, each day brings with it more weedgrowthonfieldsthatdidnotreceiverecentapplicationsofresidualherbicides.Effectiveno-tillandmodifiedno-

till planting systems (e.g., such as thosewith shallow“vertical” tillage) rely on effective weed managementviaherbicides so that surface soil evaporation canbespeeded up when the rain stops, so that corn seedplacement is not compromised while planting, andso that early weed competition with corn seedlingsdoesn’t subtract from corn yield potential. Generallyherbicide sprayers can, and in many cases should,precede tillage and planting operations that aren’tgoing to receive intensive, full-width tillage thisspring.

Weedgrowthchallengeandpondedwaterchallenge.

2. Surface roughness left after fall tillage operations in2010(oranyspring tillageoperations in lateMarchorearly April of 2011) constrains tillage options in May.

Pest&Crop No. 4 April 29, 2011 • Page 9

The dry conditions in the fall of 2010 encouragedmore extensive, aswell as deeper, fall primary tillageoperations than are normally achieved in Indiana.Although some of the initial soil roughness will havedissipated with freeze-thaw and wetting/drying cyclessince the last tillage operation, rougher soil surfaceswillrequiredeeperandmoreintensivesecondarytillagebeforeplanting.Effectively,soilconditionsneedtobefitdowntoandatleastafullinchbelowtheintendedtillagedepth before secondary tillage is advised.So farmerswillneedtobemorepatientindelayingsecondarytillageoperations if theyhavefieldswith roughsoilsurfaces.

Wetandroughfieldswhichwillneedsecondarytillageforlevelingpurposesoncethesurfacesoildries.

3. Stale seedbed planting often reduces seedbedcompaction damage and enables earlier planting.Althoughstaleseedbedplantingisatthecoreofstrip-till systems, rain-delayed planting following full-widthtillageoperations is less frequent. Insituationswherethe soil surface is smooth enough to permit plantingcorn seed at uniform depths, and where timely weedcontrolcanbeachieved,staleseedbedplantingshouldbeconsidered.Soilswithhighclaycontent,slowdryingcapability (perhaps compounded by inadequate sub-surfacedrainage),andlowaggregatestructuralstabilityareoftenidealsoilsforstaleseedbedplanting.Thosesamesoilsarealsothoseatmostriskofexcessiveclodsandunevenseedbedmoistureconditions ifsecondarytillageis imposedtooearly.Thestaleseedbedsystempermits earlier planting because planting can startassoonas thesurfacesoildriesoutandseed furrowopeningcanoccurwithminimalside-wallcompactionintherowzone.It isunfortunatethat inadequatefundinghas constrained research on various stale seedbedplanting options (e.g., following deep ripping alone,disking,chiselplowingorfallverticaltillage)toverifytherelativecornyieldbenefitsofthissystem.Nevertheless,preliminary and unpublished results frommy programhavesuggestedcornyieldscanbeequalwithplanting

on stale seedbeds versus that following recentsecondarytillage.Ifequalcornyieldscanbeachievedwhen for stale seedbed and traditional secondarytillagewhen the planting date is similar, then there iseven more opportunity for corn yield gains with staleseedbedplantingiftheplantingdatecanbeadvanced.

4. A single, shallow, and well-timed tillage operation ispreferred if pre-plant tillage is deemed necessary. Itis crucial that secondary tillage depth be limited tothe minimum necessary for successful corn plantingbecausesoilcompactionriskanddry-clodriskincreasewhen spring tillage is at deeper depths. There isno inherent benefit to corn production from doingsecondary tillage any deeper than 3 inches.Similarly,there is very little likelihood of any yield advantageaccruingfromasecondorthirdsecondarytillagepass;ifanything furtherdelayingcornplantingwill limityieldpotential more than what can be gained by multiplesecondary tillage passes. As long as the first tillageoperation followingweeks of rain delays is done at asoilmoistureconditionwhentillagecanmakeasuitableseedbed,andwhenemergedweedscanbekilled,nofurthersecondarytillageoperationsshouldberequired.

5. No-till cornplanting remainsa viable option.Certainlyifcornwillfollowsoybeaninrotation,andthesoybeanstubble has been undisturbed since harvest, no-tillcornplanting intooptimumsoil conditionsmaybe thepreferred option. The probability of successful yieldswith no-till does not decline with later planting dates;if anything, the relative yield potential of no-till cornincreases versus corn yields likely to be achievedaftermore intensive tillage operations. Nevertheless,successful no-till planting presumes the corn farmerhas a capable planter, a soundmanagement strategy(e.g., for nutrients and pest control), adequate sub-surface drainage, and sufficiently dry soils (e.g. noside-wallsmearing)duringtheplantingoperationitself.

Wetandsmoothfieldsthatwouldbeagoodcandidateforpossibleno-tillorstaleseedbedplanting.

Pest&Crop No. 4 April 29, 2011 • Page 10

6. Verticaltillagesystemsmaybeabletospeedsurfacesoildrying.Typicallyshallowandhigh-speed“verticaltillage”operationsmayhelptospeeduptherateofsurfacesoildryingwhenthereisnon-uniformresiduecoverorrain-mattedresiduecover.Thesetools,althoughgrowinginpopularityintheEasternCornbeltforatleastadecade,havenotreceivedsufficientresearchattentionbecauseoffundingconstraints.Thelimitedcornyieldresultswithsuchsystems in trialsconductedbyPurdueUniversitytodatehavebeen inconsistent. Insomecasesyieldshave been substantially superior to no-till corn, but inothercasesequaltothosewithno-till.Therearerisksassociatedwithverticaltillage;theseincludetheriskofsoilcompactionassociatedwithtractortires(ortracks)or thecoulters themselves (evenwhenoperatedat1”or2”depths)ifthesoilconditionsarenotfitfortillage.However,verticaltillagecanhelpmakethesurfacesoilmoisture contents more uniform across sloping fieldsat the timeof planting, and thatmayhelp toadvancetheplantingdatecomparedtoacompletelyundisturbedno-till planting system (especially in fields with non-uniform drainage, and in high residue situations).

7. Spring strip-tillage operations should also be shallow.Fall strip tillage (done properly) will generally offerearlier corn planting opportunities than that which islikely following spring strip-till or undisturbed no-till.Yet,iffarmerscanwaituntilsoilconditionsarefitdownto a 4-inch or 5-inch depth, and have the equipmentoptions to do shallow strip-till in spring, there can becorn yield advantages associated with doing so. Incontrast with fall strip-till, with spring strip-till there isless need to achieved a raised berm in the intendedcorn rows, but a greater need to use rolling basketsor other firming devices to retain soil moisture atseeding depths. Spring strip-till depths should be nodeeper than 5 inches, should be timed so that cornplanting follows spring strip-tilling before excessiveseedbedmoisture lossoccurs,andshouldnot involveapplicationsofexcessive ratesofbandednitrogen(N)andpotassium(K

2O) fertilizers. Highratesof recently

applied N and K fertilizers in the strip-tilled zone will

Lakesinfieldsthatneedtodrainbeforetillagecanbecontemplated.

compromise corn seedling establishment (especiallywhen dry conditions prevail following corn planting).

8. Precise automatic guidance tools provide newopportunities to limit soil compaction in the actualcornrows.Althoughthereisaninherentriskfromsoilcompactionbythetillagetool itself, therecanbeevenbigger risks associated with wheel track compaction.Adjustments like reduced tire inflation pressures canhelp, but an even more important factor can be theuse of controlled traffic systems in any pre-plantingtillageand fertilizerapplications.Useof theRTK (realtime kinematic) steering systems enable corn farmerswith such systems to precisely control where thewheel trackswill occur prior to planting. Even thoughdiagonal secondary tillage operations are sometimespreferred for helping achieve additional soil leveling,this spring it might bemore essential to practice anyrequired tillage precisely parallel to the intended cornrows,andusingthesamewheeltracksasthatintendedfor the planting tractor. Higher soilmoisture contentsatdepth than thatexperienced inmore typicalspringspotentiallymeangreateryieldbenefitsfromlimitingsoilcompaction (especially that directly under the rows).

Seedfurrowsmearingwhileplantingcorncanaddtopoten-tialdroughtstressdamagelaterintheseason.

Conclusions:

Overall, themostessentialaspectsof tillagemanage-ment for corn planting in Indiana and surrounding statesoverthenextfewweekswillbetoexercisecaution,controlweeds,andenhanceseedbedqualitywherepossible.Theworst possible combinationwouldbedoing secondary till-agewhenthesoiliswet,andhavingthatfollowedbyhotanddryconditionsduringearlydevelopmentofcornseedlings.

Themostimportantpartoftillagesystemchoicefollow-ingperiodsofexcessivespringrain is to limitsoildamageandthecreationofanyroot-restrictingsoillayers(duringei-therthetillageorthecornplantingoperations).Itisessen-tialtoleavethesoilcondition(followingtillageandplantingoperations) with the maximum opportunity for unimpededcornrootdevelopment.Potentialcornyieldsin2011canbecompromisedmorebypoorsoilstructurefollowingpoortill-

Pest&Crop No. 4 April 29, 2011 • Page 11

agechoices(whetherthetoolitself,operationtiming,depth,and frequency) from now on than they have been by theplantingdelaysthusfar.

Eastern Cornbelt farmers can’t control the rainfallamountsorrainfalltimingontheirfields.[Iftheycould,theywould gladly have shared all of their rain from the last 2weekswithwheatandcornfarmersinKansasandTexas.]Butcorn farmersdohavecontrolover tillage/plantingsys-tems, and those choices now represent the principal soilmanagementdecisionsrequiredtogetcornplantsoff toahealthy,thoughdelayed,startin2011.

Inthelong-term,tillagesystemchoicesbycornfarmersmotivatedbybotheconomicandsoilsustainabilityconsid-erationswillhavetocontendwithkeepingsufficientresiduecovertocontainsoilerosionandimprovesoilsurfacestruc-tural stability and porosity. But short-term shifts (such asthoseoutlinedabove)fromtheoriginallyintendedtillageop-erationsmightneedtobeadoptedthisspring.

“Safe” Hybrid Maturities for Delayed Corn Planting in Indiana – (Bob Nielsen)

It seemsearly to begin fearmongering about the pos-siblenecessityofswitchingtoearlierrelativehybridmaturi-ties, but the similarities of this planting seasonwith otherlateplantingyearsismakingsomefarmersfidgetalittleastheyimpatientlywaitforfieldstodryout.Oneofthebiggestagronomic concernswith severely delayed planting is therisk of the cropnot reachingphysiologicalmaturity beforeakillingfallfreezeandtheyieldlossesthatcouldresult.Aneconomicconcernwithdelayedplanting is theriskofhighgrainmoisturesatharvestandtheresultingcosts incurredbydryingthegrainorpricediscountsbybuyers.

The tables that accompany this article list “safe” rela-tivehybridmaturitiesforcornplantedthroughoutthemonthofMaybasedontheirheatunitrequirements(adjustedforplantingdate)andanticipated“normal”accumulationofheatunits between planting and an average date (50%proba-bility) of a killing fall freeze.BecauseGDDaccumulationsaregenerallylessand“usual”fallfrostsoccurearlierinthenorthernandeastcentralareasofIndiana,delayedplantingforceshybridmaturity changesearlier thanotherareasofthestate.However,evenforthoseareasofIndiana,seriousdeparturesfrom“typical”hybridmaturitiesneednotbecon-sidereduntillaterinMay.

Thematurities listed in Table 1 are those that shouldreach physiologicalmaturity at least by theweekwhen akillingfallfreezeoccurs,whileTable2listshybridmaturitiesthatshouldmatureatleastoneweekPRIORtoakillingfallfreeze.Whenmakingadecision toplanthybridmaturitiesthatareunusuallyearlyforyourareaofthestate,maketheefforttoidentifyhybridswithgooddiseaseresistancetraits.

Table 1. Approx. “safe” relative hybrid maturities for late planting dates in Indiana with the objective that physiological maturity occurs at least by the week of the expected fall frost date.

Planting date

Crop Rpt

District

“Typi-cal” CRM

Expect-ed Fall Frost Date 1-May 15-May 31-May

Approx. “safe” relative maturity

NW 109 6-Oct 113 112 109

NC 109 6-Oct 113 112 108

NE 109 6-Oct 111 109 106

WC 112 13-Oct 118+ 118+ 118

C 112 13-Oct 118+ 118+ 116

EC 109 6-Oct 114 112 109

SW 116 20-Oct 118+ 118+ 118+

SC 113 13-Oct 118+ 118+ 118+

SE 113 13-Oct 118+ 118+ 118+

50pctfallfrostriskdate

Table 2. Approx. “safe” relative hybrid maturities for late planting dates in Indiana with the objective that physiological maturity occurs at least one week before the expected fall frost date.

Planting date

Crop Rpt

District

“Typi-cal” CRM

Expect-ed Fall Frost Date 1-May 15-May 31-May

Approx. “safe” relative maturity

NW 109 6-Oct 111 110 106

NC 109 6-Oct 111 109 106

NE 109 6-Oct 108 107 104

WC 112 13-Oct 118+ 118+ 116

C 112 13-Oct 118+ 118 113

EC 109 6-Oct 111 110 106

SW 116 20-Oct 118+ 118+ 118+

SC 113 13-Oct 118+ 118+ 118+

SE 113 13-Oct 118+ 118+ 118+

50pctfallfrostriskdate

TheCropReportingDistrictsare thosedefinedbytheNa-tionalAg.StatisticsService,USDA, for Indiana.Theacro-nym“CRM”referstoComparativeRelativeMaturityasde-finedbyPioneerHi-Bred.

Recognize thatwhile thehybridmaturities listed inei-ther table should safelymature by their respective dates,severelydelayedplantingswilllikelymatureatalatertimeinthefallwhenfurthergraindryinginthefieldtypicallyoccursataproverbialsnail’space.Thus,grainmoistureatharvest

Pest&Crop No. 4 April 29, 2011 • Page 12

fordelayedplantingsmaybeunacceptablyhighintermsofboththeeaseofharvestandthecostsofartificiallydryingthegrain.

Farmers can mitigate this aggravation somewhat byplanting even earlier maturity hybrids, but recognize thattheremaynotbeasgreatofadifferenceingrainmoisturecontentasyouthink.Typically,aone“day”differenceinrela-tivematurity ratingequals 0.5percentagepoint differencein grainmoisture content at harvest (Nielsen, 2009).Thatmeanstherewillonlybeabout2pointsdifferencebetween,say,a106-dayhybridanda110-dayhybridatharvest.

Related References

Nielsen, Bob. 2002 (rev). Estimating Yield and DollarReturnsFromCornReplanting.PurdueUniv.CooperativeExtensionServicepublicationAY-264-W.Onlineat<http://www.agry.purdue.edu/ext/pubs/AY-264-W.pdf>. [URL ac-cessedApr2011].

Nielsen,R.L.(Bob).2009.InterpretingCornHybridMa-turityRatings.CornyNewsNetwork,PurdueUniv. [online]<http://www.kingcorn.org/news/timeless/HybridMaturity.html>.[URLaccessedApr2011].

Nielsen,R.L.(Bob)andPeterThomison.2003.DelayedPlanting&HybridMaturityDecisions.PurdueUniv.Cooper-ativeExtensionPublicationAY-312-W.[On-line].Availableat<http://www.agry.purdue.edu/ext/pubs/AY-312-W.pdf> [URLaccessedApr2011].

Nielsen, Robert L., Peter R. Thomison, Gregory A.Brown,AnthonyL.Halter,JasonWells,andKirbyL.Wue-thrich. 2002. Delayed Planting Effects on Flowering andGrainMaturationofDentCorn.Agron.J.94:549-558.

Thoughts on Seeding Rates for Corn –(Bob Nielsen)

Bottom line:•MostIndianacorngrowersshouldaimforeconomicfinal stands no less than about 30,000 plants peracre.

Readthefullarticleforthegorydetails.Of all the many agronomic management decisions a

corngrowermakeseachyear,onewouldthinkthatchoiceofseedingratewouldbeamongthesimplest.Yet,thistopiccontinuestogarneralotofattentionincoffeeshops,Internetchatrooms,thefarmpress,andincropseminars.So,ap-parentlythisdecisionisnotclear-cut.

Iwilladmitthatweagronomistsarepronetore-visitingresearch topics every 10 to 20 years, partly because wewonder whether today’s genetics respond differently thanyesteryear’shybrids.Nevertheless,Itendtobecomeskepti-calwhenmyseedcompanytellsmethatIneedtoincreasemyseedingratesinordertomaximizemycornyield.

Identifyingtheoptimumseedingrateforcornisakintoa balancing act among the various yield components thatmultiply together to determinegrain yield:Plants per acreXEarsperplantXKernelsperearXWeightperkernel.Ontheonehand,moreplantsperacreshouldequalmoreearsmoreacrewhich shouldbebeneficial for optimizing yield.Ontheotherhand,kernelnumbersperplantandweightperkernel eventually decrease with increasing plant popula-tions.That’snotgoodforoptimizingyield.Consequently,theoptimumfinalplantpopulation is thatwhichbestbalancesthebenefitofmoreearsperacrewiththedisadvantageofsmallerearsandlightergrain.Furthermore,stalkhealthandintegrity often falter as plant population increases beyondsomemaximumthreshold.

CornplantpopulationshavebeensteadilyincreasinginIndianaforthepast25yearsatapproximately300plantsperacreperyear(Fig.1).In2010,theestimatedaverageplantpopulationstatewidewas justover28,000plantsperacre(ppa).Consideringanaveragepercentemergenceof95%,thismeansthattheaveragestatewideseedingrateisprob-ablyaround30,000seedsperacre(spa).

Fig.1.ChangesinreportedcornplantpopulationsinIndi-anasince1986.

Statewide increases inplantpopulationhaveoccurredasgrowershaveshiftedfromquitelowseedingratestoin-termediateandhigherseedingrates(Fig.2).In1997,near-ly 60% of Indiana’s corn acres reported final stands lessthan25,000ppaandonly8%withfinalstandsgreaterthan30,000.Whereasin2010,only19%ofIndiana’sacreswerereportedtobelessthan25,000ppaandnearly41%oftheacreswerereportedtobegreaterthan30,000ppa.Amongthechangesthathaveallowedgrowerstosteadilyincreaseplantpopulationshasbeenthegeneticimprovementinover-allstresstolerancethathasresultedina)earsizeandker-nelweightbecoming lesssensitive to thestressof thickerstandsofcornandb)improvedlate-seasonstalkhealth.

There are those who contend that an average state-wideplant populationof28,350istoolowandthatIndianacorngrowersaremissingoutonopportunitiesforincreased

Pest&Crop No. 4 April 29, 2011 • Page 13

Fig.2.PercentofIndianacornacreswithplantpopulationswithinthreerangesoflowtohigh,1987-2010.

Fig.3.GrainyieldversusharvestpopulationforwinnersintheNCGACornYieldContest,2007-2010.

grainyieldswithincreasedplantpopulations.Seedcompa-nies, inparticular,sometimes recommend to theircustom-ers thatseeding rates should be in the neighborhood of35,000 or higher tomaximize yield and furthermore showyieldresponsedatathatappeartosupportthoserecommen-dations.Resultsofsomeuniversity researchalso tends tofavor thesehigher seeding rates.Some farmersand con-sultantspointtoevidencefromhighyieldcorncontests,likethatoftheNationalCornGrowersAssociation,thatsupportsthe need for high seeding rates to achieve yields near orabove300bushelsperacre(bpa).

Giventhesteady,butsmall,annualrateof increaseinseedingratesovertheyears(300ppa/year),somegrowersquestionwhethersuddenlyincreasingtheirseedingrateby5000ppaormoreinasingleyearisawisedecision.Whatquestions should the healthy skeptic askwhen presentedwith advice and recommendations for such high seedingrates?

Yield Response to Seeding Rates: Interpretation of the Data

Ultimately,theanswercomesdowntowhattheyieldre-sponsedatatellus.Thereinliestherub,becauseoftenwearenotprivy to theactualyield responsedatabutonly totheinterpretationofthesame.Interpretationofdatainvolvestheuseofstatisticalanalysisandstatisticalanalysisinvolvesdecisionsbytheresearcherontheappropriatemathemati-calmodelstorelyontodetermineoptimumseedingrates.

Let’sbeginwiththecoffeeshopscuttlebuttthatthewin-nersoftheNCGACornYieldContestareallusingseedingratesof40,000orhigherinordertoachievethose300+bpacontestwinningentries.Whileitistruethatafairnumberofthosewinnersuseexceptionallyhighseedingrates,itisalsotruethatthereisnotmuchofarelationshipbetweengrainyield and harvest population among thoseNCGAContestwinners(Fig.3).

Let’smoveon to interpretationof yield responsedatafromseedingratetrials.Tomathematicallydescribetheyieldresponsetoplantpopulation,therearealternative“shapes”ormodelsofresponsecurvestochoosefrom(Fig.4).Fromastatisticalperspective,more thanonemodelmay “fit”ordescribetheresponsedatawell.Thispresentsachallengetotheresearchertothendeterminewhichmodelmostac-curatelydescribestheyieldresponsedata.

Fig.4.Alternativemathematicalmodelsthatcanbeusedtodescribetheyieldresponsetoquantitativevariableslike

seedingrateornitrogenfertilizerrate.

If youare still readingat this point, youmaywell ask“Whocaresaslongasthemodelisagoodstatisticalfit?”.Itmattersbecausetheequationthatdescribesthemodelissubsequentlyusedtocalculateorpredicttheoptimumrate.Differentequationscanleadtodifferentanswersandthosedifferent answersmay result in different economic conse-quences for thegrowerwho implements the resulting rec-ommendation.Anexamplemayhelpillustratethisquandary.

Figure 5 depicts the yield reponse to a range of sixseedingrates.Thegraphclearly illustrates thatgrainyieldincreaseswithhigherseedingrates,butseemstoleveloutbeyondabout30,000ppa.

Pest&Crop No. 4 April 29, 2011 • Page 14

Fig.5.Anexampleofgrainyieldresponsetosixseedingrates.

Onecould“fit”astraightline(simple linear response curve)modeltothedatasetandfairlyaccuratelydescribetheyieldresponsetoseedingrate(Fig.6).The“R2”valuedisplayed beneath the line is the statistical value that de-scribeshowwelltheequationfortheline“fits”thedataset.The closer this value is to “1”, themore accurately it de-scribes thedataset.Forsomefield research,an “R2”val-ueof0.61wouldbeprettyacceptable.Ifyouacceptedthislinearresponsemodel,youwouldconcludethatgrainyieldwouldcontinueto increaseasseedingratesincrease, i.e.,theskyisthelimit.

Fig.6.Alinearresponsemodel“fit”tothesameyieldre-sponsedata.

Figure7usesaquadratic response curvetodescribethedataset.Thecurveitselfsuggeststhatyieldincreasestoamaximum,thendecreasesatseedingratesbeyondthemaximum.The“R2”valueforthisresponsemodel(0.94)isbetterthanforthelinearresponsemodeland,frankly,mostresearcherswouldbeexcitedtoseesuchagoodstatisticalfit.

Figure8 illustratestheuseofaquadratic-plateau re-sponse curve to describe the samedata set.Themodelsuggeststhatyieldsincreasewithincreasingseedingratestoapoint,thenlevelsoutathigherseedingrates.The“R2”valueforthisresponsemodel(0.997)impliesthatthemodelalmost perfectly describes the yield response to seedingrate, although technically the simpler quadratic responsecurvewith an “R2” value of 0.94 is a perfectly acceptablestatistical“fit”tothedataset.

Fig.7.Aquadraticresponsemodel“fit”tothesameyieldresponsedata.

Fig.8.Aquadratic-plateauresponsemodel“fit”tothesameyieldresponsedata.

So, here is the quandary.Twoofthepossibleresponsemodels do an excellent job of statistically describing yieldresponse toseeding rate.Statistically,youcan’tgowrongwitheitherone.However,

• Ifyouacceptedthequadraticresponsemodel,theop-timumseedingratepredictedfromtheequationwouldbe39,000ppa.

• Ifyouacceptedthequadratic-plateauresponsemodel,theoptimumseedingratepredictedfromtheequationwould be 32,000 ppa or 7,000 fewer plants per acrethantheoptimumratecalculatedfromthesimplerqua-draticresponsemodel.

Using a fairly common seed cost of $3 per thousand($240/80kbag),followingtherecommendationbasedonthequadratic responsemodelwould translate toanadditional$21peracreinseedcostforthegrowerwithnoassurancethatyieldswouldactuallybeanyhigher than if thegrowerhadusedthelowerseedingraterecommendationbasedonthequadratic-responsemodel.

Bottom Line

The consequence of this simple example is that re-searchersbeararesponsibilitytogrowerstocarefullyana-lyzeandinterpretyieldresponsestoquantitativecropinputs

Pest&Crop No. 4 April 29, 2011 • Page 15

suchasseedingratesornitrogenfertilizerrates.Basedonmy interpretationof yield responsedata frombothuniver-sityandcommercialseedingratetrials,Iconcludethatyieldresponseof today’shybrids toseeding ratescanoftenbedescribedbyquadratic-plateaumodels.

With thatpremise, Ibelieve that thedatasuggest thatmost Indiana corn growers should be targeting final plantpopulations no less than 30,000 ppa or seeding rates ofaround33,000spa.Theprimaryexceptiontothisinterpreta-tionwouldbethosesoilsorgrowingconditionsthatseverelylimit yield potential (e.g., droughty sandy soils). For thosechallengingconditions,targetedplantpopulationsshouldbeclosertothemid-20’s.

One Last “Fly in the Ointment”

Having gone to all the trouble to discuss differencesinyieldresponsemodels,letmetossoutthiscurveballtothe story.Since 2001, I have conducted 19 field-scale tri-als throughout thestateevaluatingcornyield response toseedingrates.Thesedatarepresentsevenindividualgrow-ingseasonsandthirteendifferentlocationsaroundthestate.Some of these have been on Purdue’s outlying researchfarms,othershavebeenincollaborationwithon-farmcoop-erators.Harvestplantpopulationsinthesetrialshavemostlyranged from themid-20’s to the low 40’s (thousand ppa).Theaggregateddataforgrainyieldresponsetoplantpopu-lationare illustrated inFig.9.Across those19 trials, yieldresponsetoplantpopulationhasessentiallybeenflat.

Fig.9.Corngrainyieldresponsetoplantpopulation.Nine-teenfield-scaletrialsthroughIndianasince2001.

Technically, Ican“fit”aquadratic-plateaumodeltothedatasetthatpredictsanoptimumfinalstandof30,203ppa,butthe“R2”valueforthisresponsemodelisonly0.06whichmeansthereisnotmuchofarelationshipwiththedata.Intheabsenceofastatisticallysignificantresponsecurve,myinterpretationof thedata fromthose19trials is thatyieldsfromharvestpopulationsgreaterthan30,000ppawerenohigher thanyields fromharvestpopulationsof30,000ppaorless.

Opportunities for On-Farm Research

Thenearly flat yield response toplantpopulation rep-resentedbythese19trialsisthereasonIamencouragingfolks toconsiderparticipating incollaborativeseeding ratetrialsyet thisyearandbeyond tohelp furtherdefinegrainyieldresponsetoplantpopulation.Ifrainhaskeptyoufromplantingyetthisseason,thereisstilltimetothinkaboutanon-farmseedingratetrial.Downloadtheprotocolforthisat<http://www.agry.purdue.edu/ext/ofr/protocols/PurdueCorn-SeedingRateProtocol.pdf>andcontactmeforadditionalin-formation.

Pest&Crop No. 4 April 29, 2011 • Page 16

W e a t h e r U p d a t e

It is the policy of the Purdue University Cooperative Extension Service that all persons have equal opportunity and access to its educational programs, services, activities, and facilities without regard to race, religion, color, sex, age, national origin or ancestry, marital status, parental status, sexual orientation, disability or status as a veteran. Purdue University is an Affirmative Action institution. This material may be available in alternative formats.1-888-EXT-INF <http://www.the-education-store.com>