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The Sunflower Production Guide
DISEASESEARLY SEASON DISEASESDowny Mildew
Downymildewiscapableofkillingorstuntingplants,reducingstandsandcausingsevereyieldlossesduringwetyears.
Host Crops
Sunflower
Biology
Downymildewiscausedbyasoil-borne,wind-borneandseed-bornefungiPlasmopara halstedii,whichcansurviveforupto10yearsinsoil.Undercool,water-saturatedsoilconditions,thesporesgerminateuponcontactwithsunflowerroots,enter,andspreadthroughouttheentireplant.Thisissystemicinfection.Systemicinfectionoccursonlywhentherootsarelessthan2incheslongwhentheycontactthefungi.Sunflowerplantssurvivingtheinitialinfectionwillproducewhitesporesontheundersideofcholoroticareasonleaves.Thewhitesporesareair-borne,anduponlandingonsunflowerleavesmaycausesecondaryinfections.Secondaryinfectionsaremostcommonwhensunflowerleavesremainwetforprolongedperiodsoftime.Plantsaresusceptibletosecondaryinfectionsforamuchlongerperiodoftimeversussystemicinfectionsviarootinfection.Asinfectedplantsrotandaretilledintothesoil,thefungusformstherestingstagewhichwillgerminateduringfavorableconditionsinsubsequentyears.
Figure 38. Seedling Sunflower with downy mildew.
Figure 39. Downy Mildew causes stunting and heads to face straight upwards.
Diseases|37
The Sunflower Production Guide
Symptoms
Symptomscanvaryconsiderablydependingonamountofinoculum,theageandhostorganattackedandenvironmentalfactors.Symptomscanbebroadlyclassifiedasthosecausedbysystemicorlocalizedinfections.Rootinfectionofseedlingsoryoungplantsresultsinsystemicinfection.Severelyinfectedplantsmaydiebeforeorshortlyafteremergenceorintheseedlingstage.Typicalsystemicsymptoms(Figure38)inseedlingsincludedwarfing,yellowingoftheleavesandtheappearanceofwhite,cottonymassesonthelowerandsometimesupperleafsurfaceduringperiodsofhighhumidity.Whenseedlingsareinfectedseveralweeksafteremergence,orafungicideseedtreatmentinhibitsratherthanpreventsinfection,theplantsstartshowingsymptomsatthefour-,six-,oreight-leafstage;thisistermed‘delayedsystemicinfection’.Theseplantsmayormaynotdeveloptypicaldownymildewleafsymptoms,butaretypicallystuntedwiththickened,clublikeroots.Theheadsofthefewplantsreachingmaturityfacestraightupwardsandseldomproduceviableseed(Figure39).Airbornedownymildewsporescancauselocalizedsmall,angularfoliarlesionswiththewhitefungalgrowthontheundersideoftheleaf.Theseinfectionsgenerallyhaveminimalimpactonyield.
Yieldlossesmaybesubstantial.Ifinfectedplantsaredispersedrandomlythroughoutthefield,yieldlossesprobablywillnotbeobservedunlessinfectionexceeds15percent.Neighboringplantscancompensateforseverelyinfectedplantsbygrowinglargerheads.Whenthediseaseisinalocalizedarea,suchasalowspotinafieldandallplantsareinfected,yieldlosscanbesubstantial.
Scouting Techniques
Infectedplantscanmostoftenbefoundaloneorinstandingwater.
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CONTROL TIPS
Resistantvarietiesareavailable;however,duetothedevelopmentofnewraces,resistancemaynotbeasufficientmanagementtoolinallfields.Fungicideseedtreatmentscanbeaneffectivemanagementtoolfordownymildew,butaswithgeneticresistance,thepathogenhasdevelopedresistancetometalaxylandmefanoxam,twoofthemostcommonlyusedfungicides.Otherseedtreatmentoptionsareavailableandmorewillbelabeledinthefuture.RefertothecurrentissueoftheGuidetoCropProtectionforupdatedinformationonproductsandratesforapplication.Othermanagementproceduresaretocontrolweedhostswhichincludewildandvolunteersunflowerstohelpreduceinoculum.
The Sunflower Production Guide
FOLIAR DISEASESRust
Earlyinfectionofsusceptiblevarietiescandecreaseheadsize,seedsize,oilcontentandyield.Confectionhybridsaremoresusceptiblethanoil-seedtypes.
Hosts
Wildsunflowerandcultivatedsunflower
Biology
SunflowerrustiscausedbyPuccinia helianthi.Infectioncanoccuratanytimeduringthegrowingseason,dependingontheinoculumsourceandenvironmentalconditions.Conditionsfavorableforinfectionarefreewaterontheleaves,eitherfromrainfallordew,andwarmtemperatures.Aminimumoftwohoursofwetleavesissufficientforrustinfection;sixtoeighthoursofleafwetnessresultsinthemaximumamountofinfection.Sunflowerrustsporesoverwinteronthedebrisfrominfectedsunflowerleavesandstemsofpreviouscrops.Inthespringsporesgerminatetoinfectvolunteerseedlings,wildsunflowerornewyoungplantsinnearbyfields.Underfavorableconditions,sporeproductionandinfectioncanoccurcontinuouslywithinayear.The‘repeatingstage’isthemostdamaging,asmultiplewavesofsporesarespreadbywindtootherfieldsasconditionsallow.Asthecropripens,thesporesformtheoverwinteringstagewhichcanthenre-infectfollowingsunflowercrops.
Symptoms
Thefirstsignsofrustusuallyappearwhensunflowersareatorpastbloomasenvironmentalconditionswithinthecropcanopyaremorefavorableforinfection.Theaecialstage(Figure41)ofrustappearslatespringtosummerasclustersoforangecups.Themostcommonstageofrust(uredinia)(Figure 42)isoftenobservedwithintwoweeksoftheaecia.Thesepustulesaresmall(0.1to1mm),cinnamon-brown,canberubbedofeasilyandoccuronboththeupperandundersidesofleaves.Asthediseaseprogresses,urediniamaybefoundontheupperleaves,stemandbractsofthesunflowerplant.Inresponsetotemperature,theurediniaconverttotelia(blackspotsontheuppersurfaceofleaves)attheendoftheseasonwhichdonotruboffandaretheoverwinteringstructures.
Economic Threshold
Rustseverityontheupperfourleavesis3percentorgreater.
Diseases|39
0.5% Leaf Area Infected 1% Leaf Area Infected 2% Leaf Area Infected 5% Leaf Area Infected
Figure 40. Leaf area infected by rust.
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CONTROL TIPS
Themosteffectivewaytoavoidlossfromrustisbyplantingrust-resistanthybrids.Mostoilseedandconfectionaryhybridshavegoodtoexcellentresistancetomostracesofrust.Rotationtoothercropsisalsoausefultooltominimizeinfections,assunflowerrustonlyinfectssunflowers.Ifpossible,avoidplantingnexttoafieldthathadsunflowerslastyear;managewildsunflowersorvolunteersunflowersastheyarehostsforthedisease.Earlyseedingandshortseasonhybridscanalsohelpminimizediseaseseverity.Anyculturalpracticewhichfostersadensecanopy,suchashighplantstandsandhighnitrogenfertilization,whichtrapsdew,increaseschancesofasevererustinfectionandshouldbeavoidedifrisksarehigh.Foliarfungicidesareregisteredforrust.ConsultthecurrenteditionofGuidetoCropProtectionfor products.
Figure 41. Aecia cups on the underside of sunflower leaf.
Figure 42. Rust uredinia develop on the under-and upper-leaf surfaces.
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The Sunflower Production Guide
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The Sunflower Production Guide
Alternaria Leaf and Stem Spot
Alternarialeafspotisaubiquitousdiseaseonsenescingleavesandgenerallyoflittleconcern.Underwarmandhumidconditions,itcanhoweverbecomeaseriousdefoliatingandyieldreducingdisease.
Host Crops
Sunflower,safflowerandcocklebur
Biology
Alternariafungioverwinterondiseasedstalksandmaybeseed-borneatlowlevels.SeedlingblightscausedbyAlternariamaydevelopwhensunflowerplantsemergeinrainyweatherinAlternaria-infestedsoil.Alternariasporesarespreadbywindandsplashingwater.Thefungirequirefreewaterfor4hoursforinfectiontooccur.Leafsymptomsaremostfrequentlyobservedafterfloweringasthedensecanopyisconducivetoinfection.Onceestablished,thediseasecandevelopquicklyunderfavorableconditions.InwesternCanada,climateisnottypicallyconduciveforAlternariaepidemicsandgenerallyonlythelowersenescingleavesareaffected.
Symptoms
Darkbrownirregularspotswithdarkbrowntopurplebordersandagraycenterdeveloponleaves(Figure43).Thespotsonyoungplantsmayhaveayellowhalo.Leaflesionsmaycoalesce,causingleavestowither.Stemlesionsbeginasdarkflecksthenenlargetoformlong,narrowlesions.Thestemlesionsoftenjointoformlargeblackenedareaswhichmayresultinstembreakage.Thelesionsarelocatedrandomlyalongthestemandnotassociatedwithapetiole.
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CONTROL TIPS
Croprotationandburyinginfestedcropresidueto hastendecompositionhelpsminimizeAlternaria infection.
Figure 43. Alternaria leaf lesions close up.
Diseases|41
The Sunflower Production Guide
Septoria Leaf Spot
Septoriaiswidelydistributedonsunflowersbutusuallycauseslittledamage.Insevereinstancesitcancausedefoliationofthelowerleaves.
Host Crops
CultivatedandWildSunflower
Biology
SeptoriaiscausedbythefungiSeptoria helianthi.Thefungisurviveoninfectedcropresidueandcanalsobeseed-borne.Thediseasecanappearanytimeduringthegrowingseasonwithinitiationfavoredbymoderatelyhightemperaturesandabundantrainfall.
Symptoms
Septoriadevelopsfirstonthelowerleavesandspreadsupwardsthroughthecanopy.Thelesions(upto15mmindiameter)beginaswater-soakedareaswhicharegreasygreeninappearance.Thespotsbecomeangulartodiamondshaped,withtancentersandbrownmargins.Youngspotsareoftensurroundedbyanarrowhalothatgraduallymergeswiththesurroundinggreentissue(Figure44).Maturespotscontainsmallblackspecksorfruitingbodies.ThisisthebestwaytodistinguishAlternariafromSeptoria.Thelesionsmaycoalesceinlaterstagesandtheleafmaywitheranddie.
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44 CONTROL TIPS
Croprotation,incorporationofsunflowerresidueanduseofcleanseedarethebestmanagementpracticestomanageSeptoria.
Figure 44. Septoria lesions contain small black fruit bodies.
STALK AND ROOT-INFECTING DISEASESSclerotinia Wilt and Basal Rot
Infectedplantsdierapidly,andiftheplantdiespriortoseedmaturityitresultsinyieldloss,lowertestweight,andloweroilcontent.
Host Crops
Sclerotiniahasaverywidehostrangeofover360species,whichincludessunflowers,canola,mustard,drybeans,fieldpeas,lentilsandpotatoes.
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The Sunflower Production Guide
CONTROL TIPS
Managementofsclerotiniaisdifficultbecauseofthewidehostrange,butrotationtocerealsandcornisthemosteffectivetominimizesclerotiniainthesoil.Sunflowerhybridswithsomelevelsofresistanceareavailable.TheuseofamycoparasiteswhichfeeduponotherfungihasshowntoattackSclerotinia.OnecommerciallyavailableisConiothryium minitans(Contans).Thismycoparasitecankillsclerotiainseveralmonthsratherthanyears.
Figure 45. Sclerotinia wilt.
Figure 46. Sclerotinia Basal rot lesion.
Biology
SclerotiniaoverwintersasSclerotinia sclerotioruminthesoiloronplantdebris.Sclerotiaareirregularlyshapedstructureswhichrangeinsizeandshapefromsphericaland1/8inchindiametertoY-shapedandupto1inchinlength.Thesclerotiabodiescansurviveinthesoilfor5ormoreyears.Assunflowerrootsgrownearsclerotiniainthesoil,thesclerotiaarestimulatedtogerminateproducingmyceliumwhichinfectsthelateralroots.Sclerotiaforminthedecayedstempithandontherootsastheplantdies.Thesclerotiaarereturnedtothesoilduringtillageoperationsandserveassourcesofinoculumforthenextsusceptiblecrop.
Soilmoistureandtemperatureduringthegrowingseasonarenotcriticalfactorsaffectingtherateofincidenceofsclerotiniawilt.
Symptoms
Wilt(Figure45)canappearatanytimebetweenemergenceandmaturity,butismoreprevalentaroundflowering.Suddenwiltoftheplantoccurswheninfectedrootscannotuptakeadequatewatertomeetthedemandsoftheplant.Examinationofthestem-rootareawillrevealatan-brown,watersoakedlesionatthesoilsurface(Figure46).Thestalksandrootsmaybecomecoveredwithwhitemyceliaandhardsclerotiabodiesdevelopunderverywetsoilconditions.
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The Sunflower Production Guide
Sclerotinia Mid-Stalk Rot
Mid-stalkrotisthediseaseleastoftencausedbySclerotinia.Lodgingcancausecompleteyieldlossonaperplantbasis.
Biology
Underwetsoilconditions,thesclerotiainthesoilcangerminatetoformsmallmushroomscalledapotheciathatproduceair-bornespores.Thesporescanoriginateinthesunflowerfieldorcanbeblowninfromadjacentfields.Sporescanmovebyrainsplash,variousinsectcarriersandupto1kmbyair.Thesporesrequirefreewaterandsenescingplanttissuetogerminateandinfectplants.Mid-stalkinfectionmayresultfromleafinfectionorinfectionattheleafaxil.
Symptoms
Infectioncanoccuranytimefromseedlingtomaturitydependingonthepresenceofinfectingsporesandfavorableenvironmentalconditions.Mid-stalkrotbeginswithinfectionoftheleaf,andthefungusprogressesinternallythroughthepetioleuntilitreachesthestem.Theleaflesionsarenotuniqueenoughtoidentifythefungus,butthestemlesionsareidenticaltothatformedbyrootinfection;tancoloredandwater-soaked(Figure47).Thesclerotiacandevelopwithinthestemorontheexteriorofthestem.Leavesabovethelesionwilt,andthestalkeventuallydisintegratesbecomingshreddedasonlyvascularcomponentsofthestemremain(Figure48).
CONTROL TIPS
ThecommentsmadeaboutSclerotiniawiltalsoapplytomid-stalkrotmanagement.Culturalpracticestoavoidhighplantdensitiesbyreducingpopulationsandhighnitrogenfertilizationhelplowertheincidenceofinfection.Shalloworzero-tillagepracticesmayaidinfasterdeteriorationassclerotiaareleftonthegroundsurfaceandsubjecttoincreasedenvironmentaldeterioration.Resistancegeneshavebeenthemosteffectiveapproach,andbreedingforhighertolerancecontinues.
Figure 47. Sclerotinia mid-stalk rot lesion
Figure 48. Sclerotia bodies develop within the stem tissue or on the surface of the stem.
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The Sunflower Production Guide
Phoma Black Stem
PhomaisthemostwidespreadstalkdiseaseinthenorthernGreatPlains,but yieldlossesareconsideredminimal.
Host Crops
Cultivatedsunflower
Biology
Thefungus(Phoma macdonaldii )overwintersininfecteddebris.Phomainfectionoccursthroughoutthegrowingseason;however,itisnotusuallynoticeduntilthestemlesionsbecomeobviouslaterinthesummer.Leavescanbeinfectedbywindcarriedspores,rainsplashedsporesorsporestransmittedbyinsects.Stemweevilsaresuspectedintransmittingthefungiinternallyandexternally.Adultweevilsfeedingontheleavescauseleaflesionswhereascontaminatedlarvaespreadthefungusastheytunnelthroughoutthestem.LeaflesionsarenotdistinctiveandcanbeconfusedforAlternaria.Theleafinfectionsprogressdownthepetioletothestalk.Underfavorableconditions,theleafwilts,thepetioleturnsuniformlyblack,andthestemlesionsexpand.
Symptoms
Large,jetblacklesionsdeveloponthestem(Figure49),sometimesreachingabout4to5cminlength.Thelesionsareuniformlyblackandshinywithdefiniteborders.Smallcircularfruitingbodiesofthefungusareproducedonthesurfaceofthestembuttheserequireahandlenstosee.Thefungusmayalsoproducelesionsonthebackofthehead,ontheleaves,andatthebaseofthestalk.Stemlesionsdonotresultinpithdamageorlodgingandaregenerallyregardedassuperficiallesions.IfstemweevillarvatunnelingspreadsPhomasporeswithinthepith,extensivepithdegenerationcanoccur.
CONTROL TIPS
CulturalpracticestominimizePhomaincludesafouryearrotationtominimizetheinoculumloadinthesoil,delayedplantingandavoidinghighplantpopulationsandhighnitrogenfertilization.Controlofstemweevilscanhelpreducetransmissionofthefungusbutinsecticideapplicationisrarelyeconomicallyjustified.Somehybridsaremoretolerantthanothers,butnoneareimmunetothe disease.
Figure 49. Phoma black stem lesion
Diseases|45
The Sunflower Production Guide
Phomopsis Stem Canker
InrecentyearsPhomopsishasbecomeaveryprevalentdisease.Yieldlossesresultfromsmallerheads,lighterseedandlodgingduetoweakenedstems.
Hosts
Sunflower
Biology
Thefungi(Phomopsis helianthii)overwinteroninfectedplantdebrisandsporesarerainsplashedorwindblownontoleaves.Theinfectioninitiatesatleafmarginsoflowerleaves,developingintoabrownnecroticareaborderedbyachloroticmargin.Theinfectionspreadsdownthroughtheveinstothepetioleandfinallytothestem.ThesymptomsaresimilartothoseofVerticilliumleafmottle;however,withVerticilliumveinsremaingreen.Stemlesionsusuallydonotappearuntilflowering.Thediseaseismostsevereunderconditionsofprolongedhightemperaturesandhighrainfall.
Symptoms
Firstsymptomsinitiateonlowertomiddleleavesafterfloweringasnecroticspotswithachloroticborderonleafmargins.Thestemlesionsbeginasasmallbrownsunkenspotbutenlargesrapidlybecomingalargetantolightbrownlesionorcankercenteredonaleafpetiole.LesionsaremuchlargerthanPhomablackstem,sometimesreaching6inchesandbrownratherthanblack.Blackfruitingbodies(pycnia)formoninfectedtissue.Phomopsiscausesextensivepithdegradationandthestalkcanusuallybecrushedundermoderatethumbpressure.PhomopsisinfectedplantsaremorepronetolodgingthanPhomainfectedplants.
50CONTROL TIPS
Thoroughincorporationofthesunflowerstalksintothesoiltoburyresidueandcroprotationcanreducediseaseincidenceandseverity.CropresidueleftonthesoilsurfacefostersdevelopmentofPhomopsis.HybridsresistanttoPhomopsis,developedusingparentallinesfromEuropewherethediseaseisparticularlysevere,arecommerciallyavailable.
Figure 50. Phomopsis Stem Canker
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The Sunflower Production Guide
Verticillium Leaf Mottle
Verticilliumcansignificantlyreducesunfloweryieldespeciallyonlightersoils.Qualitymayalsobeaffectedthroughdecreasedoilcontentandseedsize.
Host Crops
Variousplantspeciescanbeinfectedincludingsunflowers,potatoes,alfalfaandsweetclover
Biology
Thefungus(Verticillium dahliae)isseed-andsoil-borne.Itsurvivesasverysmall,black,restingbodies(microsclerotia)indiseasedsunflowerdebrisandbroadleavedweeds,persistingfor5to10years.Themicrosclerotiagerminateinresponsetorootexudates.Theroottipsofsunflowerplantsareinvadedand,eventually,allpartsoftheplantbecomeinfected.Thefungusproducestoxinswhicharetranslocatedthroughouttheplantcausingthechloroticandnecroticareasbetweentheveins.Whentheplantdies,thefungusproducesblackfungalbodiesthatreturntothesoilwiththeplantdebris.
Symptoms
Symptomsusuallyarenotobserveduntilflowering,butmayappearatthesix-leafstageundersevereconditions.Initialsymptomsbeginastinychloroticflecksthatincreaseinsizewithtimedevelopingintoextensiveinter-veinalyellowing(Figure51).Symptomsbeginonthelowerleavesandprogressslowlyuptheplantandmayeventuallyinfectallleaves.Affectedleavesquicklybecomedry.Thevascularsystemmaybediscoloredbrown,apparentasaringaroundthepithincrosssection.Inseverelyinfectedplants,thepithisblackenedwithalayeroftinyblackfruitingbodies.
CONTROL TIPS
Mostoil-seedhybridscontainresistancetoVerticilliumwhereasconfectionhybridsaregenerallymoresusceptible.However,anewstrainhasrecentlybeenidentifiedinCanadaandtheU.S.whichisabletoovercomethesourceofresistanceinthesevarieties.Thediseaseismoresevereonlighterlandwithahistoryofsunflowercroppingthanonheavy,claysoil.Rotationisimportantonlightersoilwithahistoryofsunflowercroppingtoreduceinoculumloadinthe soil.
Figure 51. Verticillium Leaf Mottle
Diseases|47
The Sunflower Production Guide
HEAD ROT AND DISEASES OF MATURE PLANTSSclerotinia Head Rot
Head-rotisconsideredthemostimportantdiseaseaffectingsunflowerproduction,causingyieldandqualityloss.
Hosts
Sunflower,canola,mustard,drybeans,fieldpeas,lentils,potatoes
Biology
Sclerotiniahead-rot(Figure52)isquitevariable,usuallyoccurringlateintheseasonandinfluencedprimarilybytheamountofrainfallfromfloweringthroughtoharvesting.Aswithsclerotiniamidstalkrot,head-rotiscausedbyair-bornesporesproducedbyapothecia(smallmushrooms)eitherwithinthefieldorblownfromaneighboringfield.Thesporesrequirefreewaterandafoodbasesuchasdeadorsenescingplanttissuetogerminateandinfect.Ascosporescolonizethedeadfloretsandpollenonthefaceofthehead.Afterinfectionittakesseveralweeksuntiltheappearanceofbrownlesionsonthebackofthehead.
Symptoms
Thefirstsymptomsofheadrotusuallyaretheappearanceofwater-soakedspotsorbleachedareasonthefleshybackofthehead.Thefunguscandecaytheentirehead,withtheseedlayerfallingawaycompletely,leavingonlyableached,shreddedvascularsysteminterspersedwithlargesclerotia.Thebleached,skeletonizedheadsresemblestrawbroomsandareveryobviousinthefieldevenfromadistance.
Yieldlossfromheadrotonanindividualplantcanrangefromminimaltototallossiftheheaddisintegratesanddropsalltheseedtothegroundpriortoharvest.Intactbutdiseasedheadswillhavelightandfewerseeds,withloweroilcontentandwillshatterduringharvest.
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CONTROL TIPS
Sunflowerhybridsexhibitvariablerangeofsusceptibilitytoheadrot,butnohybridsarecommerciallyavailablewithadequateresistance.Fungicidesmayhelpreducetheincidenceofheadrot,withapplicationsmadepreventivelysinceseveralweekslapsefrominfectiontosymptomdevelopment.ConsultthecurrenteditionoftheGuidetoCropProtectionforproductinformation.
Figure 52. Sclerotinia Head Rot
The Sunflower Production Guide
Rhizopus Head Rot
RhizopusisaverywidespreaddiseaseinthecentralGreatPlains.Affectedheadswillhavealightertestweight,loweroilcontentandreducedseedyields.
Host Crops
ManyhostsforRhizopusincludingsunflower,beetsandtobacco
Biology
Susceptibilityoftheheadincreasesfromthebudstageuptothefullbloomandripeningstages.Sporesaredisseminatedbywind,rainandinsects.Rhizopusenterstheheadthroughwoundscausedbyhail,birds,insectsandhasbeenassociatedwithsunflowermidgedamage.Rapiddiseasedevelopmentoccursinwarm,humidweather.Oncetheheadisfullycolonizedandalltissuekilled,theheaddriesupandbecomes‘mummified’.
Symptoms
Initialsymptomsaresimilartootherheadrotdiseases;brown,sunken,watersoakedlesionsonthebackofthehead.Asthelesionsenlarge,theinterioroftheheadbecomesmushy(Figure53).Theinterioroftheheadbecomesfilledbymyceliuminterspersedwithblackfruitingbodiesresemblingpeppergrains.Oncetheheaddriesupitischaracterizedbyadarkbrown,pepperyappearanceoftissuesinthereceptacleandbecomesveryhard.
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CONTROL TIPS
ControllingheadinsectsisthemostefficientmethodtominimizeincidencesofRhizopusheadrot.Geneticresistancehasbeenidentified,butseverityofthediseasehasnotwarrantedintensiveresearch.RotationdoesnothelpreducetheincidenceofRhizopusduetothenumberofRhizopusspecies.NofungicidesareregisteredforcontrolofRhizopusheadrot.
Figure 53. Rhizopus Head Rot
Diseases|49
