guidelines-to-identification-and-management-of-pla

PP248GuidelinestoIdentificationandManagementofPlantDiseaseProblems:PartI.EliminatingInsectDamageandAbioticDisorders1MonicaElliott,KenPernezny,AaronPalmateer,NikolHavranek21.ThisdocumentisPP248,oneofaseriesofthePlantPathologyDepartment,FloridaCooperativeExtensionService,InstituteofFoodandAgriculturalSciences,UniversityofFlorida.OriginalpublicationdateFebruary2008.ReviewedApril2011.VisittheEDISwebsiteat(REC)--BelleGlade,FL;AaronPalmateer,assistantprofessor,PlantDiagnosticClinic,TropicalREC--Homestead,FL;NikolHavranek,biologicalscientist,EvergladesREC--BelleGlade,FL;FloridaCooperativeExtensionService,InstituteofFoodandAgriculturalSciences,UniversityofFlorida,GainesvilleFL32611.TheInstituteofFoodandAgriculturalSciences(IFAS)isanEqualOpportunityInstitutionauthorizedtoprovideresearch,educationalinformationandotherservicesonlytoindividualsandinstitutionsthatfunctionwithnon-discriminationwithrespecttorace,creed,color,religion,age,disability,sex,sexualorientation,maritalstatus,nationalorigin,politicalopinionsoraffiliations.U.S.DepartmentofAgriculture,CooperativeExtensionService,UniversityofFlorida,IFAS,FloridaA.&M.UniversityCooperativeExtensionProgram,andBoardsofCountyCommissionersCooperating.MillieFerrer-Chancy,InterimDeanIntroductionBeginningmastergardenerscanbeintimidatedbythedauntingtaskofcorrectlydiagnosingthecauseofaclient'splanthealthproblem.However,withexperienceandthedevelopmentofasystematicapproachtodiagnosis,mastergardenerswillbecomeconfidentandsuccessfulplantproblemdetectives.Planthealthproblemsresultfrom:1)plantpathogenscausingdiseases;2)insectsdamagingtheplant;or3)environmentalfactors,oftenreferredtoasabioticdisorders.Unfortunately,thesymptomsforthesehealthproblemsareoftenverysimilar.Agoodapproachtoidentificationofplantdiseaseistobeginbydeductivelyeliminatinginsectdamageandabioticdisordersaspossiblealternativecauses.InsectDamageOneofthereasonstoconsiderinsectsearlyintheidentificationprocessistherelativeeasewithwhichtheycanbefound.Manyinsects,suchascaterpillarsandbeetles,arefairlylargeandeasytospot.Evensmallerinsectslikescales(Fig.1)andrelatedparasitessuchasmitescanbereadilyseenwitha10xpowerhandlens.Insectdamageisalsoconspicuous,oftenconsistingofholesinleavesorfruit,leaveswitharaggedappearanceduetoinsectschewingalongleafmargins,ordeformedleaves(Fig.2).Figure1.OleanderScale.Signsthatinsectsareorhavebeenpresentincludefrass--thedarkcoloreddroppingstheyleaveGuidelinestoIdentificationandManagementofPlantDiseaseProblems:PartI.....2Figure2.Caterpillardamage.behind--andsootymold,associatedwithsuckinginsects.Sootymoldistheblacksuperficialgrowthofafungusonthehoneydeworothermaterialexcretedbysuckinginsects,suchasaphidsormealybugs(Figure3).Thefungusgrowingontheexcretionisnotharmfultotheplant.Whensootymoldisfound,theMasterGardenershouldexaminetheplantmorecloselyforthepresenceofinsectssuchasaphids,usingahandlensifneeded.Figure3.Sootymold.Everyeffortshouldbemadetoobservedefinitiveevidenceofinsectinvolvementwiththeplanthealthproblem.Ifathoroughsearchconsistentlyyieldsnegativeresults,thenthenextstepintheprocessofeliminationistoconsideranabioticcausefortheplanthealthproblem.AbioticDisordersInPartIIofthisseriesonplantdiseaseproblems,wewilldescribeindetailthestepstofollowinsearchingforplantpathogens(e.g.,fungi,bacteria,viruses)asthecausesofplantdisease.However,becauseconfirmationofaplantdiseasecanbetimeconsumingandmayrequiresendingthesampletoaplantdiagnosticclinic,eliminatingabioticdisorders(usuallyenvironmentalfactors)shouldbedonebeforesearchingforapathogen.Becausemostplantpathogensrequirespecificenvironmentalconditionsinorderforadiseasetodevelop,informationcollectedtodeterminewhetherthereisanabioticdisorderwillalsobeusefulformakingadiseasediagnosis.Moreover,someplantsaremorelikelytosufferfromabioticdisordersratherthanplantdiseases,sotakingabioticcausesintoconsiderationfirstmaymaketheidentificationprocesslesstime-consuming.Abioticliterallymeanswithoutlife.Abioticplantdisordersarenonbiologicalfactors,usuallyassociatedwiththeplant'senvironment,thataffectplantsadversely.Theseenvironmentalfactorsincludetemperature,moisture,soilpH,airquality,lightregime,andnutrition.Ifoneormoreofthesefactorsgoesaboveorbelowtheoptimumrangeforagivenplantspecies,plantgrowthmightbeabnormaloradverselyaffected.Abioticdisordersmayalsobecausedbyhumanactivities,suchaspesticideandfertilizerapplications.Oneimportantindicatorofanabioticcauseforaplanthealthproblemisthedistributionofthedamagewithintheenvironmentalunit.Plantsgenerallygrowindistinctenvironmentalunitssuchasvegetablegardens.Environmentalproblemsaremuchmorelikelytoaffectmostplantsintheenvironmentalunituniformly.Diseaseandinsectproblems,ontheotherhand,tendtooccurinclumpsorhotspotswithintheunit,especiallyearlyinoutbreaks.Forexample,iffrostinjuryoccursinavegetablegarden,all12tomatoplantsarelikelytohaveb