Unit 4: Plant Disease Management for Field Crops

Unit 4: Plant Disease Unit 4: Plant Disease Management for Field Management for Field

CropsCrops


CropsCrops Unit 4 Objectives:Unit 4 Objectives:

– Discuss some common plant disease Discuss some common plant disease problems of common field crops in ILproblems of common field crops in IL

– Awareness of possible Awareness of possible prevention/treatment methodsprevention/treatment methods

– Understanding of the types of chemicals Understanding of the types of chemicals or treatments necessary for controlor treatments necessary for control


CropsCrops Crop yield and quality is affected by Crop yield and quality is affected by

disease each year in ILdisease each year in IL Disease management strategies Disease management strategies

should be part of your IPM planshould be part of your IPM plan– Resistant or tolerant varieties of cropResistant or tolerant varieties of crop– Crop rotationsCrop rotations– FungicidesFungicides

Use in conjunction w/ other practices or as a Use in conjunction w/ other practices or as a last resortlast resort

– Appropriate agronomic practicesAppropriate agronomic practices


CropsCrops Success often depends on amount of Success often depends on amount of

scouting, stage of identification, and scouting, stage of identification, and accuracy of diagnosisaccuracy of diagnosis– Proper scouting will ensure that Proper scouting will ensure that

controls/treatments are used at the controls/treatments are used at the most effective timesmost effective times

– Can help prevent an economic lossCan help prevent an economic loss


CropsCrops Disease DiagnosisDisease Diagnosis

– Accurate diagnosis is critical first step for Accurate diagnosis is critical first step for controlcontrol

– Many diseases or nutrient deficiencies Many diseases or nutrient deficiencies can cause the same symptomscan cause the same symptoms

– Must correctly diagnose in order to Must correctly diagnose in order to prevent unnecessary applicationsprevent unnecessary applications

– Plants should be collected for Plants should be collected for identification as soon as disease is identification as soon as disease is suspectedsuspected Is this always realistic?Is this always realistic?


CropsCrops– Best to try to identify the disease while Best to try to identify the disease while

the plant is still alivethe plant is still alive– Samples can either be sent to the Plant Samples can either be sent to the Plant

Clinic at U of I or be taken to the local Clinic at U of I or be taken to the local Extension OfficeExtension Office

Read the LabelRead the Label– Make sure you understand all Make sure you understand all

restrictions associated w/ each chemicalrestrictions associated w/ each chemical– These chemicals may not be used as These chemicals may not be used as

frequently as herbicides or insecticides, frequently as herbicides or insecticides, so you may not be as up to date w/ so you may not be as up to date w/ themthem


CropsCrops– Must be purchased and applied by a Must be purchased and applied by a

licensed applicatorlicensed applicator Fungicide GuidelinesFungicide Guidelines

– Seed TreatmentsSeed Treatments Greatest benefits found when:Greatest benefits found when:

– Seed is low quality due to damage or fungal Seed is low quality due to damage or fungal infestationinfestation

– Seedbed is cool and wet delaying germination Seedbed is cool and wet delaying germination and emergenceand emergence

– Low seeding ratesLow seeding rates Should not be used as a substitute for good Should not be used as a substitute for good

quality seedquality seed


CropsCrops Low yields and economic losses will still be Low yields and economic losses will still be

realized w/ low quality or damaged seedrealized w/ low quality or damaged seed Selection is crucialSelection is crucial

– Some treatments may only control specific Some treatments may only control specific pathogenspathogens

– Foliar TreatmentsFoliar Treatments May reduce losses in corn, soybeans, and May reduce losses in corn, soybeans, and

small grainssmall grains Should only be used on fields w/ an expected Should only be used on fields w/ an expected

disease severitydisease severity If the disease is diagnosed early, and If the disease is diagnosed early, and

fungicide applied correctly, should have fungicide applied correctly, should have maximum benefitmaximum benefit


CropsCrops Fungicides applied to corn usually reserved Fungicides applied to corn usually reserved

for seed-production fieldsfor seed-production fields– Leaf blightsLeaf blights– Gray leaf spotGray leaf spot– Rust diseasesRust diseases– Generally justified only when disease is prevalent Generally justified only when disease is prevalent

within 1-2 weeks of tasselingwithin 1-2 weeks of tasseling– Infections occurring 1-2 weeks or later after Infections occurring 1-2 weeks or later after

tasseling usually not economically controlledtasseling usually not economically controlled

Foliar fungicides applied to small grainsFoliar fungicides applied to small grains– RustsRusts– SeptoriaSeptoria


CropsCrops– Leaf blightsLeaf blights– Tan spotTan spot– These tend to occur after inadequate rotations These tend to occur after inadequate rotations

and during damp weatherand during damp weather Most damage occurs from emergence to flag Most damage occurs from emergence to flag

leaf/early milk stageleaf/early milk stage– Fungicides can increase yields, seed weight, and Fungicides can increase yields, seed weight, and

qualityquality– Decisions to spray should be based on the Decisions to spray should be based on the

amount of disease at flag leaf emergenceamount of disease at flag leaf emergence

Use of adjuvants is recommended Use of adjuvants is recommended (especially for corn and small grains)(especially for corn and small grains)


CropsCrops Nematicide ApplicationsNematicide Applications

– Granular forms for corn and sorghum Granular forms for corn and sorghum should be applied as band treatmentsshould be applied as band treatments

– Should only be used when soil analysis Should only be used when soil analysis shows high numbers of parasitic shows high numbers of parasitic nematodesnematodes

– Not designed to replace crop rotation or Not designed to replace crop rotation or use of resistant varietiesuse of resistant varieties


CropsCrops Alfalfa Seedling BlightAlfalfa Seedling Blight

– Caused by soil-borne fungiCaused by soil-borne fungi– Often occurs under wet conditionsOften occurs under wet conditions– Usually the first disease stress alfalfa Usually the first disease stress alfalfa

may encountermay encounter– Often leads to poor or stunted standsOften leads to poor or stunted stands

May survive, but yields will be reducedMay survive, but yields will be reduced


CropsCrops– Easy way to suspect is if alfalfa stand Easy way to suspect is if alfalfa stand

emerges, but weeds grow quickeremerges, but weeds grow quicker Alfalfa usually grows very aggressively and Alfalfa usually grows very aggressively and

crowds out weedscrowds out weeds


CropsCrops Alfalfa Root rotsAlfalfa Root rots

– Phytophthora, Fusarium wilt, Phytophthora, Fusarium wilt, AphanomycesAphanomyces

– Causes poor seedling stands, as well as, Causes poor seedling stands, as well as, root damageroot damage

– Identified by lesions on the taproot, Identified by lesions on the taproot, subsequent disintegration of root tissue, subsequent disintegration of root tissue, and deathand death

– Control w/ resistant varietiesControl w/ resistant varieties


CropsCrops Corn Gray Leaf SpotCorn Gray Leaf Spot

– Early symptoms are signified by 1/16” olive Early symptoms are signified by 1/16” olive spots on the leaves w/ a yellow halospots on the leaves w/ a yellow halo

– At two weeks the spots are their signature gray At two weeks the spots are their signature gray or tan coloror tan color ¾ to 2 ½” long¾ to 2 ½” long Run parallel to leaf veinsRun parallel to leaf veins Begins on lower leaves and can spread upwardBegins on lower leaves and can spread upward Entire leaf may appear gray under extreme Entire leaf may appear gray under extreme

conditionsconditions

– Moist conditions and 70-85 degrees are idealMoist conditions and 70-85 degrees are ideal


CropsCrops Corn Stalk RotCorn Stalk Rot

– FusariumFusarium Leaves turn from healthy green to dull greenLeaves turn from healthy green to dull green Lower stalk yellowsLower stalk yellows Stalk easily collapses and will cause lodgingStalk easily collapses and will cause lodging Inside of the stalk may be pinkInside of the stalk may be pink Favorable conditionsFavorable conditions

– Dry earlyDry early– Above avg. rain midseasonAbove avg. rain midseason– Temps 80-100 degreesTemps 80-100 degrees

– Many other types of stalk rot are knownMany other types of stalk rot are known


CropsCrops Soybean Brown Stem RotSoybean Brown Stem Rot

– Soil borne disease that becomes visible Soil borne disease that becomes visible late in the seasonlate in the season

– Survives on plant material that may be Survives on plant material that may be buried >1’ deepburied >1’ deep Infects the roots and stem early in lifeInfects the roots and stem early in life Grows w/ the plantGrows w/ the plant Often infects the xylem tissue and restricts Often infects the xylem tissue and restricts

nutrient and water passage as the plant nutrient and water passage as the plant maturesmatures


CropsCrops– SymptomsSymptoms

Typically not visible until late reproductive Typically not visible until late reproductive stagesstages

May not be visible at allMay not be visible at all Internal browning of vascular tissue in stem Internal browning of vascular tissue in stem

and/or leavesand/or leaves Leaves may have appearance similar to high Leaves may have appearance similar to high

temperature scorchingtemperature scorching May occur in circular patternsMay occur in circular patterns

– Favorable weather conditionsFavorable weather conditions Cool wet conditions either in early Cool wet conditions either in early

development or at reproductive stagesdevelopment or at reproductive stages Development inhibited above 80ºDevelopment inhibited above 80º


CropsCrops Soybean Phytophthora Root RotSoybean Phytophthora Root Rot

– Spores reside in the soilSpores reside in the soil Germinate under wet conditions to form Germinate under wet conditions to form

more sporesmore spores Mobile w/ soil waterMobile w/ soil water Encysts on soybean rootsEncysts on soybean roots

– SymptomsSymptoms Stand reduction either pre or Stand reduction either pre or

postemergencepostemergence Leaves may wiltLeaves may wilt Water soaked lesions on stem and/or rootsWater soaked lesions on stem and/or roots


CropsCrops– Favorable ConditionsFavorable Conditions

>60º temps>60º temps Very wet soilsVery wet soils

– Poorly drainedPoorly drained– Low areasLow areas– Compacted soilsCompacted soils– High clay soilsHigh clay soils– Not restricted to these areas onlyNot restricted to these areas only


CropsCrops Soybean Cyst NematodeSoybean Cyst Nematode

– Very similar symptoms to many other Very similar symptoms to many other diseasesdiseases Can go undetected as the cause of economic Can go undetected as the cause of economic

loss for many yearsloss for many years

– Will often occur in circular/oval shaped Will often occur in circular/oval shaped patternspatterns Infected plants will be less vigorous and Infected plants will be less vigorous and

somewhat yellowsomewhat yellow May be slow to fill foliageMay be slow to fill foliage


CropsCrops– Severity of symptoms can vary greatly Severity of symptoms can vary greatly

from nonexistent to very visiblefrom nonexistent to very visible– Infections cause dwarfed and stunted root Infections cause dwarfed and stunted root

systemssystems Can reduce the number of nitrogen-fixing Can reduce the number of nitrogen-fixing

nodesnodes Roots may be susceptible to other diseasesRoots may be susceptible to other diseases

– True identification can only be done by True identification can only be done by root examinationroot examination White/yellow oval shaped eggs on the rootsWhite/yellow oval shaped eggs on the roots Nodes are much smaller than the nitrogen Nodes are much smaller than the nitrogen

nodesnodes


CropsCrops Asian Soybean RustAsian Soybean Rust

– Severe foliar damageSevere foliar damage Destroys photosynthetic tissueDestroys photosynthetic tissue Early defoliationEarly defoliation Early maturationEarly maturation

– Yield losses can be 10-80%Yield losses can be 10-80%– 6 hours of wet conditions and temps 59-6 hours of wet conditions and temps 59-

82º ideal for germination82º ideal for germination Dry conditions will restrict itDry conditions will restrict it


CropsCrops– Spores penetrate cells directly instead Spores penetrate cells directly instead

of wait for another opening in the leafof wait for another opening in the leaf 9-10d from initial infection to next stage of 9-10d from initial infection to next stage of

spore productionspore production

– Common hosts include kudzu, vetch, Common hosts include kudzu, vetch, yellow sweet cloveryellow sweet clover

– Spreads w/ wind patternsSpreads w/ wind patterns


CropsCrops Wheat Septoria Leaf BlotchWheat Septoria Leaf Blotch

– Recognized by oval shaped lesions on Recognized by oval shaped lesions on the leavesthe leaves Centers of the lesions may be grayishCenters of the lesions may be grayish May ooze when squeezed under high May ooze when squeezed under high

humidity conditionshumidity conditions

– Spores only mobile by splashing Spores only mobile by splashing raindropsraindrops

– Also infect stems and headAlso infect stems and head Head become purple-streakedHead become purple-streaked


CropsCrops– Can result in low test weight and Can result in low test weight and

shriveled seedsshriveled seeds– Usually survives on straw and inoculates Usually survives on straw and inoculates

the following crop yearthe following crop year– Favorable conditions:Favorable conditions:

Splashing rainsSplashing rains Temps between 68-82ºTemps between 68-82º


CropsCrops Wheat Fusarium Head Blight (Scab)Wheat Fusarium Head Blight (Scab)

– Caused reduced yield and grain qualityCaused reduced yield and grain quality– May also contaminate grain w/ mycotoxinsMay also contaminate grain w/ mycotoxins

Vomitoxin – not extremely toxic when fed, but Vomitoxin – not extremely toxic when fed, but will decrease consumption and feed efficiency will decrease consumption and feed efficiency (non ruminants most sensitive)(non ruminants most sensitive)

– Favorable conditions:Favorable conditions: Humid during floweringHumid during flowering

– Identified by bleached spikelets of the Identified by bleached spikelets of the headhead May even kill the developing seed in the dough May even kill the developing seed in the dough

stagestage


CropsCrops Unit 4 Assignment:Unit 4 Assignment:

– Create a treatment protocol for each of Create a treatment protocol for each of the discussed diseasesthe discussed diseases Product and active ingredientProduct and active ingredient Application rateApplication rate Application methodsApplication methods Time of applicationTime of application

– Bring an article on a plant diseaseBring an article on a plant disease One page written summaryOne page written summary

– 20 points -- Due next time!20 points -- Due next time!

Documents

Unit 4: Plant Disease Management for Field Crops