wheat disease identification and control -
TRANSCRIPT
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Wheat Disease Identification and Control
MELVIN NEWMAN, ProfessorPlant Pathologist
Entomology and Plant Pathology Department
UNIVERSITY OF TENNESSEE
2009
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Objectives To present detailed information on
key identification symptoms of wheat diseases.
To discuss control measures of the most important wheat disease.
To present related research data for control.
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Scab (head blight)Fusarium graminearum
Favored by warm, wet weather during and after flowering.
Bleached heads or individual spikelets Superficial pink/orange mycelium/spores Bleached heads contain scabby seed
(tombstones). Black lesions may be present at the base
of the head.
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Scab
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Head Scabcaused by the fungusFusarium spp.(pink or orangespore mass)
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Scab on wheat
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Fusarium leaf spot
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Wheat Scab Control
No resistant varieties Plant varieties that differ in flowering
times Bury crop residue Chopping corn stalks down helps Crop rotation ( not corn or grain
sorghum) Foliar fungicides are not effective
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Foliar and Head Diseases
Glume Blotch – Stagonospora (Septoria) nodorum. Found mostly on the lower leaves and then on the heads. Hard to scout for and fungus becomes more aggressive as heading occurs. Favored by frequent rains and mid-70s.
Symptoms – On glume are chocolate-brown, with small, black pycnidia and are diagnostic as seed become mature. Grain may be extremely shriveled.
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Glume blotchLeaf blotchSeptoria tritici Stagonospora nodorum
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Glume Blotch
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Leaf Blotch
Stagonospora leaf blotch with pycnidia
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Stem rust Leaf rustPuccinia graminis Puccinia recondita
Use Resistant Varieties for Control of Leaf Rust and/or foliar fungicides
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Stripe Rust of Wheat
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Stripe Rust Caused by Puccinia striiformis Symptoms appear early in the spring. Rust pustules are yellow and arranged into
long conspicuous stripes. Spores are blown in from warmer areas. Disease development is most rapid under cool,
wet weather. Varieties differ widely in susceptible. Fungicides (triazoles) are effective if applied
before disease infects upper leaves.
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Powdery Mildew
Erysiphe graminis
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Powdery Mildew on Wheat
Erysiphe graminis
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Foliar Disease Control in Wheat
Use foliar fungicides if appropriate
Rotate cropsPlow under old crop residue if
appropriateTreat seed with fungicidesUse tolerant varieties if available
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Take-all showing thewhite head symptom
This can be confused with head scab
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Take-all fungusin young wheat roots showing theblack root rot Symptom.Caused by:Gaeumannomycesgraminis
healthy infected
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Take-all
Rotted stems & roots
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Take-all
Dark hyphae in rootsGaeumannomyces graminis
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Take-All Disease Control
Later plantings are better Use Ammonium Nitrate Fertilize early Use higher rates of fertilizer Do not lime take-all infested soil Rotate with other crops, corn may
produce scab in wheat
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Barley Yellow Dwarf Virus Transmitted by several species of aphids Fall infection causes the greater yield
loss. Symptoms usually do not show up until
spring. Symptoms: Stunted, poorly tillered across
a field. Yellow, red or purple coloration of leaves after extended warm weather in April
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Barley Yellow Dwarf Virus
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Barley Yellow Dwarf VirusBarley Yellow Dwarf VirusBarley Yellow Dwarf VirusBarley Yellow Dwarf Virus
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Greenbug aphids
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BYDV CONTROL IN WHEATWith seed treatments of Imidacloprid insecticide
WTES, Jackson, TN 1993-2001Yields in bushels/acre
Gaucho 480 F
1993 1994 1995 1996 1997 1998 1999 2000 2001
Untreated 62 96 40 69 65 48 78 72 73
1.0 oz 66 99 44 68 59 60 78 75 80
1.5 oz 67 103 50 63 62 58 78 76 76
Increase 1.0 oz
4 3 4 0 0 12 0 3 7
Increase 1.5 oz
6 7 10 0 0 10 0 4 3
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BYDV Control
Avoid early plantingThere are no resistant
varietiesUse insecticide to control fall
aphids
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Wheat StreakMosaic VirusSpread by the Wheat leaf curlmite
Curl mite
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Wheat curl mite, vector of Wheat Streak Mosaic Virus
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Control of WSMV
Control the Wheat Curl miteBreak the “green bridge”Destroy volunteer wheatBurn down any grasses 2 weeks
before planting wheat.
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Wheat Spindle Streak Virus(WSSV)Spread by the soil-borneFungus Polymyxa graminis
Use resistant varieties. Damage is usually notsevere, especially when temperatures stay above65 F.
Control
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Seed Treatments for Disease Control in Wheat
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Six Reasons to Treat Wheat Seed with a Fungicide
6. To reduce loose smut5. To reduce powdery mildew4. To reduce seedling disease3. To increase germination2. To reduce scab1. To increase yield
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Seed Treatment Fungicides Seed rots & seedling diseases (Rhizoctonia,
Fusarium): Charter (Triticonazole), captan, difenoconazole (Dividend), fludioxonil (Maxim), PCNB, tebuconazole (Raxil), thiram
Damping-off diseases ( Pythium spp.): metalaxyl, mefenoxam
Smuts ( loose smut ): carboxin, difenoconazole, tebuconazole
A combination material is needed, especially for adverse planting conditions or no-till.
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aphids
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BARLEY YELLOW DWARF (BYD) SPREAD BY AT LEAST 20 APHIDS SPP. MAJOR APHIDS: OAT BIRD-
CHERRY,CORN LEAF, ENGLISH GRAIN, GREENBUG, AND RICE ROOT APHID
FIVE PROMINENT STRAINS OF BYDV: RMV, RPV, MAV, PAV, SGV
OVER 80 GRASS SPECIES ARE SUSCEPTIBLE.
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Why Should Aphids be Controlled in the Fall ?Aphids carry the Barley Yellow Dwarf
Virus (BYDV), and young seedlings are very susceptible.
Yield loss can be significant in some years.
Once aphids feed on young seedlings, it is too late to control BYD.
Scouting for aphids is difficult in the fall.
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BYD CONTROL IN WHEATWith seed treatments of imidacloprid (Gaucho) insecticideA.Y. Chambers,WTES, Jackson, TN 1993-2001Yields in bushels/acre; rate in ozs./cwt
Gaucho 480 1993 1994 1995 1996 1997 1998 1999 2000 2001
Untreated 62 96 40 69 65 48 78 72 73
1.0 oz 66 99 44 68 59 60 78 75 80
1.5 oz 67 103 50 63 62 58 78 76 76
Increase 1.0 oz
4 3 4 0 0 12 0 3 7
Increase 1.5 oz
6 7 10 0 0 10 0 4 3
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BYD ControlAvoid early planting.There are no resistant varieties.Use insecticides to control fall
aphids. Spring aphids do not cause as
much damage.
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Summary of Wheat Disease Control Practices
• Plant after Oct. 15.• Use recommended resistant varieties.• Treat seed with fungicide and insecticide to
control aphids in the fall.• Wheat after corn may provide inoculum for scab• Do not lime Take-All infected fields, acid soils
have less Take-All.• Burn down any “green bridge” 2 weeks before
planting.• Treat with foliar fungicides when wheat prices
and disease conditions warrant their use.