Crop Diseases in Corn, Soybean, and Wheat Karen Rane and Gail Ruhl Department of Botany and Plant Pathology Purdue University West Lafayette, IN 47907 Email: rane@purdue.edu, ruhlg@purdue.edu Page 2

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SEED and HEAD DISEASES

WHEAT Disease Name: Common Bunt (Stinking Smut) Pathogen: Fungus. Tilletia caries, T. foetida Symptoms: Infected heads remain green longer than uninfected heads, glumes may be spread apart, infected seed appear dark and have a fishy odor; internal tissues replaced by masses of black fungal spores. Conditions: Disease is favored by cool temperatures and moist conditions. Therefore, more common and severe in wheat sown in the fall. Inoculum Survival: Seedborne and soilborne spores. Inoculum Dispersal: Seedborne and airborne spores. Management: Pathogen-free seed, fungicide seed treatment, resistant cultivars.

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WHEAT Disease Name: Loose Smut Pathogen: Fungus. Ustilago tritici Symptoms: Infected heads are blackened with a dry, powdery mass of fungal spores. Entire seed is replaced by lack fungal spores. Conditions: Disease is favored by cool to moderate temperatures and humid conditions. Infections only occur during flowering. Inoculum Survival: Internal seedborne mycelium. Inoculum Dispersal: Airborne spores. Management: Pathogen-free seed, systemic fungicide seed treatment, resistant cultivars.

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WHEAT Disease Name: Septoria Glume Blotch Pathogen: Fungus. Leaf and glume blotch: Septoria nodorum (Leptosphaeria nodorum), and leaf blotch: S. tritici (Mycosphaerella graminicola) Symptoms: Chlorotic (yellow) water-soaked flecks becoming dry, yellow, then red-brown lesions. S. nodorum lesions are round. S. tritici lesions are blocky with tiny black specks (pycnidia) visible in rows in mature lesions. Conditions: Cool, wet, windy weather favors S. tritici development. Warm wet weather favors S. nodorum. Inoculum Survival: Infected crop residues, seed, voluteer wheat, some grassy weed hosts. Inoculum Dispersal: Seedborne spores. Management: Pathogen-free seed, fungicide seed treatment, resistant cultivars, crop rotatation, foliar fungicides. Destruction of infested straw, stubble, and volunteer wheat.

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WHEAT Disease Name: Scab (Head blight) Pathogen: Fungus. Fusarium graminearum Symptoms: Spikelets appear bleached often with a pale pink tint, tombstone kernels, seed light weight, sometimes infected spikelets are barren, can produce mycotoxin, seedling blight. Conditions: Disease development is favored by warm, moist conditions during and shortly following flowering, may be more severe where wheat follows corn because the pathogen also causes Giberella ear and stalk rot. Inoculum Survival: Infected residues, seed, and soil. Inoculum Dispersal: Airborne spores. Management: Crop rotation, seed treatments for seedling blight phase, burying infected residues by plowing.

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VIRUS DISEASES

WHEAT Disease Name: Barley Yellow Dwarf Pathogen: Virus. Barley yellow dwarf virus (BYDV) Symptoms: Stunting, mosaic, yellowing tip and margins inward and downward. Flag leaf yellowing with spring infection. Conditions: Cool, dry conditions that favor aphid vectors. Fall infection more damaging than spring infection. Inoculum Survival: Infected plants and weed hosts. Inoculum Dispersal: Vectors (aphids). Management: Tolerant wheat cultivars, planting after fly-free date.

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WHEAT Disease Name: Soilborne Wheat Mosaic Pathogen: Virus. Soilborne wheat mosaic virus (SBWMV) Symptoms: Mild green to yellow mosaic with parallel streaks on lower leaves. yellow-green mottling, dashes, and streaks. Reddish streaking and necrosis at leaf tips sometimes occurs. Stunting can be moderate to severe. Conditions: Favored by long periods of fluctuating temperatures in early spring. Inoculum Survival: Soilborne fungal vector (Polymyxa graminis). Inoculum Dispersal: Soilborne fungal vector (Polymyxa graminis). Management: Resistant cultivars, planting after fly-free date.

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WHEAT Disease Name: Wheat Yellow Mosaic (Wheat spindle streak mosaic) Pathogen: Virus. Wheat yellow mosaic virus (WYMV) Symptoms: Yellow-green mottling, dashes, and streaks on lower leaves. Reddish streaking and necrosis at leaf tips sometimes occurs. Fewer tillers, seeds, and heads. Mild stunting. Conditions: Long periods of fluctuating temperatures in early spring. Inoculum Survival: Soilborne fungal vector (Polymyxa graminis). Inoculum Dispersal: Soilborne fungal vector (Polymyxa graminis). Management: Tolerant cultivars.

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