Wheat Disease Identification Guide - University of Idaho Extension ...

ContentsDiseases affecting heads and grainCommon bunt.......................................................................... 1Fusarium head blight................................................................ 2Loose smut............................................................................... 3Sooty head molds...................................................................... 4Stagonospora nodorum blotch.................................................. 5Diseases affecting leavesBacterial streak......................................................................... 6Barley yellow dwarf................................................................... 7Leaf rust................................................................................... 8Powdery mildew....................................................................... 9Septoria tritici blotch...............................................................10Stagonospora nodorum blotch.................................................11Stem rust................................................................................ 12Stripe rust.............................................................................. 13Tan spot..................................................................................14Wheat soilborne mosaic.......................................................... 15Wheat spindle streak mosaic....................................................16Wheat streak mosaic...............................................................17Diseases affecting stem and rootsCephalosporium stripe............................................................18Common root rot.....................................................................19Fusarium root, crown, and foot rots........................................ 20Take-all................................................................................. 21

Loose smutThe normal head tissue of plants infected by loose smutis completely replaced with dark masses of fungal spores,giving the heads a black powdery appearance. It ispossible to see heads damaged by loose smut while muchof the head is still inside the boot. Only the central stemof the head is left after the spores are released.Management: Fungicide seed treatment, disease-freeseed sources.Diseases affecting heads and grain3

Disease affecting leavesBacterial streakEarly symptoms of bacterial streak include small, watersoakedareas between leaf veins. These water-soakedareas become tan streaks within a few days. Whenthe disease is severe, streaks may merge to form large,irregular areas of dead tissue. When dew is present, thebacteria causing this disease may ooze from the lesionsand dry to form a clear, thin film. This film flakes easilyand is visible when the leaf is viewed from differentperspectives.Management: Avoid highly susceptible varieties.6

Disease affecting leavesLeaf rustSmall, orangish-brown lesions are key features of leafrust infections. These blister-like lesions are mostcommon on leaves but can occur on the leaf sheath,which extends from the base of the leaf blade to the stemnode. Lesions caused by leaf rust are normally smaller,more round, and cause less tearing of the leaf tissue thanthose caused by stem rust.Management: Genetic resistance, foliar fungicides.8

Powdery mildewPowdery mildew causes white lesions on leaves and leafsheaths. Glumes and awns also can be infected whendisease is severe. Fungal growth is largely limited toouter plant surfaces and can be easily wiped away byrubbing a finger across affected areas. Mature lesionsmay have dark, reproductive structures mixed with thewhite, cottony growth of the fungus.Management: Genetic resistance, foliar fungicides.Disease affecting leaves9

Disease affecting leavesSeptoria tritici blotchThis fungal disease causes tan, elongated lesions onwheat leaves. Lesions may have a yellow margin, butthe degree of yellowing varies among varieties. Thedark, reproductive structures produced by the fungus arekey diagnostic features and can often be seen withoutmagnification. This disease is also known as speckledleaf blotch.Management: Genetic resistance, foliar fungicides, croprotation.10

Stagonospora nodorum blotchThe lesions of Stagonospora leaf blotch are normallybrown or tan, surrounded by a thin, yellow halo. Lesionscaused by Stagonospora leaf blotch are more irregularin shape and often have a darker color than those oftan spot. The presence of small, honey-colored fungalreproductive structures is diagnostic for Stagonosporanodorum blotch; however, these reproductive structuresare only visible with considerable magnification.Management: Genetic resistance, foliar fungicides, croprotation, fungicide seed treatment.Disease affecting leaves11

Disease affecting leavesStem rustStem rust causes blister-like lesions on leaves, leafsheaths, and stems. Infection of glumes and awns is alsopossible. The reddish-brown spores of the fungus causeconsiderable tearing as they burst through the outerlayers of the plant tissues. Mature stem rust lesions aremore elongated than those of leaf rust.Management: Genetic resistance, foliar fungicides.12

Stripe rustStripe rust causes yellow, blister-like lesions that arearranged in stripes. The disease is most common onleaves, but head tissue also can develop symptoms whendisease is severe. Outside the United States, this diseaseis sometimes referred to as yellow rust.Management: Genetic resistance, foliar fungicides.Disease affecting leaves13

Disease affecting leavesTan spotThe key diagnostic feature of tan spot is tan lesionswith a yellow margin. Mature tan spot lesions oftenhave a dark area in the center. Lesions may merge asthey expand, resulting in large sections of diseased leaftissue. The fungus that causes tan spot survives in thedebris of previous wheat crops and produces small, blackreproductive structures in the spring.Management: Avoid planting into wheat residue, tillagewhere appropriate, genetic resistance, foliar fungicides.14

Wheat soilborne mosaicWinter wheat infected by wheat soilborne mosaicdevelops a pale-yellow discoloration shortly after breakingdormancy in the spring. The incidence of wheat soilbornemosaic is often greater in low areas of a field, wheremoist soil conditions favor growth of the protozoa thatspread this viral disease. Leaves of infected plants oftenhave a mosaic pattern of dark green blotches on a paleyellowbackground. Symptoms normally fade when warmweather slows the viral activity within infected plants.Management: Genetic resistance.Disease affecting leaves15

Disease affecting leavesWheat spindle streak mosaicWheat spindle streak mosaic causes a yellowdiscoloration to wheat seedlings. This yellowdiscoloration is often most intense in the wettest areasof a field. Leaves of infected plants have long, yellowstreaks that are slightly wider in the middle than at theirends. Symptoms are similar to wheat soilborne mosaic,and plants often are infected with both diseases.Management: Genetic resistance.16

Wheat streak mosaicLeaves of plants infected with wheat streak mosaic havea bright yellow streaking. Symptoms are often mostsevere near the leaf tip. The virus that causes wheatstreak mosaic survives in volunteer wheat and is spreadby wheat curl mites. The disease is often most severein areas of a field that are closest to these sources ofthe disease and mites. Commonly, plants infected withwheat streak mosaic also are infected with High Plainsdisease and Triticum mosaic. The symptoms of thesediseases are nearly identical. Disease severity is greaterwhen plants are infected by more than one virus.Management: Control volunteer wheat, delayedplanting date, genetic resistance, avoid planting nearmaturing corn.Disease affecting leaves17

Diseases affecting lower stem and rootsCephalosporium stripePlants infected with Cephalosporium stripe havepronounced yellow stripes running the full length ofthe leaf blade. The center of the yellow stripe may havea long, brown streak that extends onto the leaf sheath.Splitting the stem of infected plants often reveals small,brown streaks within the node tissue. Cephalosporiumstripe also can cause areas of stunted, irregular growthwithin a field. Often, infected plants die prematurely,causing patches of white heads within a field.Management: Genetic resistance, crop rotation, controlgrassy weeds.18

Common root rotCommon root rot causes premature death of wheat,resulting in patches of white heads scattered throughouta field. Infected plants are often dark at the base andhave poor root development. A key diagnostic featureof common root rot, however, is dark-brown lesions onthe thin stem extending from the base of the plant tothe remnant of the seed. This thin stem is known asthe “subcrown internode.” Healthy subcrown internodesshould be cream colored and firm.Management: Crop rotation, control grassy weeds.Diseases affecting lower stem and roots19

Diseases affecting lower stem and rootsDiseases affecting lower stem and rootsFusarium root, crown, and foot rotsFusarium root, crown, and foot rots cause patches ofwheat to die prematurely, resulting in areas of whiteheads within a field. Infected plants are typically brownat the base and have poor root development. Duringadvanced stages of the disease, the Fusarium fungusoften produces a pink, cottony growth inside the lowerportions of the stem. Often, the disease is most severeafter prolonged periods of dry weather.Management: Crop rotation, control grassy weeds.20

Take-allThis fungal disease causes wheat to die prematurely,resulting in patches of white heads in otherwise greenfields of wheat. Plants infected by take-all normallyhave a black discoloration of the lower stem and roots.Frequently, the disease is most severe in wet areas of afield and near field edges where the fungus survives inassociation with grassy weeds.Management: Crop rotation, control grassy weeds.Diseases affecting lower stem and roots21

AcknowledgementsThis publication was developed by the multi-stateextension and research committees for small graindiseases, NCERA-184 and WERA-97. Publicationauthors: Erick De Wolf, James P. Shroyer, and BrianOlson, Kansas State University. Photo credits: ErickDe Wolf, Bill Bockus, James P. Shroyer, and Bill Willis,Kansas State University; Tim Murray, WashingtonState University; and Marcia McMullen, NorthDakota State University. The USDA-NIFA ExtensionIntegrated Pest Management program award 2009-41533-05331 sponsored development and distribution ofthis publication.For additional assistance identifying diseasesof wheat contact:Juliet MarshallCereals Cropping Systems,Agronomy and PathologyAssistant ProfessorUniversity of Idaho, Idaho Falls1776 Science Center Drive Suite 205Idaho Falls, ID 83402-1575(208) 529-8376This publication was developed and distributed with the assistance of the U.S. Department ofAgriculture (USDA). The USDA prohibits discrimination in all its programs and activities on thebasis of race, color, national origin, age, disability, and where applicable, sex, marital status,familial status, parental status, religion, sexual orientation, genetic information, politicalbeliefs, reprisal, or because all or part of an individual’s income is derived from any publicassistance program.March 2011