Wheat Diseases

8/2/2019 Wheat Diseases

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WHEAT DISEASE NOTES 2007-2008

Alfredo Martinez, Assistant Professor and Extension Plant Pathologist.Plant Pathology Department.Dewey Lee, Professor and Extension Agronomist. Department of Cropand Soil SciencesUniversity of Georgia

1. WHEAT DISEASE INCIDENCEON 2006-2007 GROWINGSEASON.Drier than expected environmentalconditions, during the 06-07growingseason rendered an overalldecrease in disease incidence.Puccinia recondita (leaf rust) was

present in low amounts. Blumeriagraminis f. sp. tritici (powderymildew) incidence was moderatebut weather conditions and earlyspray of fungicides helped to avoidan epidemic. Dry conditionsimpacted other diseasesappearance. Fusarium spp. (causalagent of fusarium foot rot) andGaumannomyces graminis var.tritici (take-all) were found incentral and southern Georgia and

may have contributed to the earlydecline of some fields.Stagonospora (Glume blotch onheads and leaves) incidence waslow during the season. However, anincrease on calls to specialists andsamples submitted to the Plantdisease clinic were observed inlocalized areas on diseases such asloose smut caused by Ustilagotritici, and black point caused by

Alternaria spp. Loose smut

incidences can be attributed tountreated seed plantings. Barley Yellow Dwarf Virus (BYDV) wasvariable throughout the state, withlow amounts observed in SouthGeorgia. From the Piedmont andnorth, the damage was moderate.Sporadic samples with soilborne

wheat mosaic virus symptoms wereobserved last season.Disease dynamics observed duringthe past growing season canprovide important information onpossible disease scenarios and toimplement scouting activities on atimely manner during this growingseason. More educated decisions on

disease prevention andmanagement can be made.

2. DISEASE IDENTIFICATIONAND MANAGEMENT FOR THE2007-2008 SEASONDisease data for all therecommended varieties for Georgiaare found in the current 2007Georgia Wheat Production Guide orGeorgia Small Grain VarietyPerformance Test Bulletin. As

indicated in an earlier UGA wheat

management update, seed supplywas extremely short in 2007. Therewere many varieties currentlyoffered for sale in Georgia that arebetter adapted for the mid-south(Missouri, Arkansas, Tennessee, etc)and they may have variable diseaseresponse compared to thoseadapted to Georgia. Therefore isimperative to remain vigilant and

contact your local county Extensionoffice at the first sign of disease.Begin scouting fields when the plantreaches GS 32-37 (Feekes GS 7-8).In general, powdery mildew andstripe rust will likely appear first. Ifno disease is present by GS 58(Feekes 10.5) but expected, due toconducive environmental


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conditions, then apply the properrate of Quilt, Stratego, Headline

or Quadris to maintain the highyield potential and test weight. Seethe Georgia Pest Control Handbookor Wheat Production Guide for rate

and timing information. Rememberfungicides do not increase yield.

They only help you to preserve theyield and test weight.

3. DISEASES OF WHEAT UNDERWARM, LOW RAINFALLENVIRONMENTAL CONDITIONS

DRYLAND FOOT ROTThis disease is also called Fusariumfoot and root rot, common foot rot,

brown root rot, and crown rot.

CauseFusarium graminearum and F.culmorum are most commonFusarium species associated withwater-stressed wheat. These twospecies can survive in the soil andwheat debris as thick-walled,asexual resistant spores calledchlamidospores

Symptoms and SignsFusarium cause the root, crown andlower nodes and internodes ofwheat plants to turn brown androtted and a purplish discolorationof the stem is readily observed.Foot rot tends to be most severe onridges and slopes where soils aredrier. Plants that are severelydiseased mature early producemostly shriveled seed, appearbronzed, bleached or/and havewhiteheads. In the early stages ofdisease development and under theright conditions, a pinkishdiscoloration may appear inside theleaf sheaths.

Disease Cycle The fungi responsible for dryland

foot rot are ubiquitous. They aregood saprophytes in tissues theypreviously parasitized, and canmultiply rapidly on infested wheatresidues. Chlamydospores maypersist in soil for months. Primary

infections occur on coleoptiles,subcrown internodes and primaryand secondary roots. Drought andwarm temperatures predisposewheat to dryland foot rot. Plantsstressed by freezing or Hessian fliesare also subject to attack. Thedisease can be severe in wheatreceiving too much fertilizer for theamount of rainfall available,especially in areas receiving lessthan 16-18 inches per year.

ControlSeedling infections are reduced byusing clean or chemicallydisinfected seed. Also, late-autummseeding is recommended todecrease seedling exposure towarm soil temperatures. Reducedseedling infection, is not guaranteeagainst infection at later stages.Establish nitrogen application rateson soil tests for residual nitrogen,

and avoid excessive use of nitrogenfertilizer. Clean cultivationdiscourages development of grassweeds and speeds breakdown ofinfested crop residues. Crop rotationis advised to limit alternative hosts.

This practice help limit the buildupof pathogen populations in the soil.


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ReferencesWiese, M. V. 1987. Compendium ofWheat Diseases. APS Press.Maloy, O. C., and Inglis, D.A.1993. Dryland foot rot.http://pnw-

ag.wsu.edu/smallgrains/Dryland%20Foot%20Rot.html

4. WHEAT DISEASE REVIEWIf favorable environmental

conditions are present(irrigated wheat or rainfallevent, combined withproper temperatures), leafrust con be problematicearly in the season.

Leaf Rust - Puccinia reconditaf.sp. tritici

Disease Symptoms:Small pustules about one-sixteenthinch in diameter with flaky redspores develop rapidly on leaves.Pustules may be found early in thegrowing season on lower leaves, butthey usually appear in large

numbers on the upper leaves afterflowering.

Signs:Pustules with red, flaky sporesbreak the leaf surface. Theurediospores are round to slightlyoval, slightly rough, and easilydislodged.

Conditions Favoring Disease:Leaf rust is favored by temperatures

from 60 to 80F. Because infectionoccurs quickly, brief showers orovernight dew are sufficient forinfection to begin.

Disease Management:Leaf rust is best controlled byplanting resistant cultivars. Because

the disease develops quickly andnew races can develop frequently, itis important to know thesusceptibility of a cultivar (seeannual CAES Small GrainsPerformance Tests Research Report

or the Wheat Production Guide).Plant several resistant cultivars toreduce the risk of severe disease.Control volunteer wheat which canbecome infected in late summerand serve as a local source ofspores. Avoid early planting toreduce fall infection. Foliar-appliedfungicides are very effective for useon susceptible cultivars (see GAPest Control Handbook). Applyfungicide when the uppermost leaf

has emerged for best control.

SHAPE \* MERGEFORMAT

2. Barley Yellow Dwarf Virus.Warmer temperatures can initiateaphid activity earlier in the season,therefore increasing the potentialfor Barley Yellow Dwarf Virusincidence.Barley yellow dwarf virus (BYDV) is
http://www.ent.uga.edu/pmh/http://www.ent.uga.edu/pmh/http://www.ent.uga.edu/pmh/http://www.ent.uga.edu/pmh/


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probably the most widelydistributed virus in wheat. It isestimated to reduce yields by 5 to25% each year. The symptoms arevariable and resemble nutritionalproblems or frost damage. Usually

the discoloration is characterized byvarious shades of yellow orreddening from the tips to the baseand from the leaf margin to themidribs of the leaves. Somevarieties have more yellowsymptoms whereas others havemore red to purple discoloration.When infection begins early in theseason, after heading theuppermost leaf is often veryupright. Severe infection usually

causes some stunting and reductionin numbers of seeds per head.BYDV is transmitted by severalaphid species. Aphids acquire thevirus by feeding on infected plantsfor very short periods and thenmove to other uninfected plants.Infection can occur any time whenviruliferous aphids multiply andmigrate in fields. Crop rotation isless effective for barley yellowdwarf because aphids can transmit

the virus between fields, and manygrasses on which the aphids feedalso harbor the virus.Barley yellow dwarf can causesevere losses in many Georgiafields, most often following a mildfall and winter which allows aphidsto be active and transmit the virusearly in plant development. BYDV ispresent in nearly all fields eachyear. Disease severity depends onaphid populations and theproportion of aphids that cantransmit the virus. Control ofvolunteer wheat and grassy weedsduring the summer and along theedges of fields may slow initialinfection. Planting during the latterpart of the recommended periodcan delay fall infection. Resistant

varieties and insecticide applicationto control aphids can reducedamage from barley yellow dwarf(see Insect Management).

5. WHEAT DISEASE RESOURCES

For more information on wheatdisease identification andmanagement resources you can useor visit

1. Field Crops Disease Library athttp://plantpath.caes.uga.edu/extension/DiseaseLibrary.html#field

2. Buntin, G. D., and Cunfer, B.

2000. Southern Small GrainsResource ManagementHandbook. UGA Bulletin 1190

3. 2007-208 Wheat ProductionGuide. Lee, D. et al 2007. CSS-05-10 September 2007.
http://plantpath.caes.uga.edu/extension/DiseaseLibrary.html#fieldhttp://plantpath.caes.uga.edu/extension/DiseaseLibrary.html#fieldhttp://plantpath.caes.uga.edu/extension/DiseaseLibrary.html#fieldhttp://plantpath.caes.uga.edu/extension/DiseaseLibrary.html#fieldhttp://plantpath.caes.uga.edu/extension/DiseaseLibrary.html#fieldhttp://plantpath.caes.uga.edu/extension/DiseaseLibrary.html#field

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Wheat Diseases