Crop Diseases in Corn, Soybean, and Wheat Gail Ruhl Department of Botany and Plant Pathology Purdue University West Lafayette, IN 47907 Email: ruhlg@purdue.edu Page 3

EAR ROTS

CORN Disease Name: Fusarium Ear Rot Pathogen: Fungus. Fusarium moniliforme Symptoms: Seldom involves whole ear, rot usually occurs at tip of ear or in scattered areas on ear, color of fungal mycelium around infected kernels varies from white to faint pink to reddish brown. Infected kernels vary in color from light to dark brown. Conditions: Dry, warm weather. Infection occurs through injury by insects or environmental stress. Inoculum Survival: Infected crop residue (stalks, seeds), infected seed, soil. Inoculum Dispersal: Airborne spores. Management: Resistant hybrids (avoid sowing hybrids with weak seed coats or poor husk cover), crop rotation, clean plowing, harvest grain early, dry corn to 15% moisture content and below to prevent further mold growth in storage.

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CORN Disease Name: Aspergillus Ear Rot Pathogen: Fungi. Aspergillus flavus, A. glaucus, A. niger Symptoms: Aspergillus niger appears as a black mold on infected kernels. A. flavus is a greenish-yellow mold growing on damaged kernels. A. glaucus is a greenish mold. Conditions: A. flavus is more common in Indiana following hot, dry weather, injury by drought stress and insect damage. Mold growth in storage when moisture is higher than 18%. A. flavus can produce a carcinogenic secondary metabolite known as aflatoxin. Inoculum Survival: Infected plant residue, infected seed, soil. Inoculum Dispersal: Airborne spores. Management: In storage, controlled by drying corn to a moisture content below 15% as soon after harvest as possible. In the field, avoid insect or mechanical damage to ears.

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OTHER DISEASES

CORN Disease Name: Maize Dwarf Mosaic Pathogen: Virus. Maize dwarf mosaic virus (MDMV) strain A or B Symptoms: Stippled mottle or mosaic of light and dark green on the youngest leaves (may develop into narrow streaks). Upper internodes may be shortened. Older leaves may become blotched with red streaks. Conditions: Those favorable to aphids and growth of Johnsongrass in fields. Inoculum Survival: Weeds (rhizomes of perennial Johnsongrass). Inoculum Dispersal: Vectors (several aphid species). Management: Resistant hybrids, control rhizome Johnsongrass or other overwintering weed hosts.

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CORN Disease Name: Maize Chlorotic Dwarf Pathogen: Virus. Maize chlorotic dwarf virus (MCDV) Symptoms: Fine chlorotic striping is first evident on smallest visible leaf veins. Older leaves may exhibit reddening, yellowing and marginal necrosis. Conditions: Those that favor leafhopper reproduction and growth of Johnsongrass in fields. Inoculum Survival: Weeds (rhizomes of perennial Johnsongrass). Inoculum Dispersal: Vector (leafhopper Graminella nigrifrons) Management: Resistant varieties. Sow early in the growing season to avoid large leaf hopper populations. Control perennial Johnsongrass.

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CORN Disease Name: Crazy Top Pathogen: Fungus. Scleropthora macrospora Symptoms: Partial to complete replacement of the normal tassel by a large, bushy mass of small leaves. No pollen is produced. Ear formation may also stop, causing ear shoots to be numerous, elongated, leafy and barren. Plants may be stunted or taller than average. Conditions: Saturated soil conditions for 24-48 hours. Inoculum Survival: Infected corn residue, wild grasses. Inoculum Dispersal: Waterborne spores in saturated soil. Management: Provide adequate soil drainage, control grassy weeds, avoid sowing in low, wet spots.

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