| Key to Major Corn Diseases in Ohio | ||||
|---|---|---|---|---|
| Disease | Symptoms | Environmental Conditions Favoring Disease | Method of Infection & Transmission | Management |
| Seed rots Seedling blights |
Poor emergence; killing of embryo before germination; rotting of seedling roots; yellowing, wilting, and death of seedling leaves. | Disease prevalent in poorly drained soil during periods of cold, wet weather: soil temperatures below 50°F to 55°F favor seedling blight. | Fungi persist in soil. | Use high-quality uncracked seed; chemical seed treatment; proper seed bed preparation. |
| Stewart’s bacterial wilt and leaf blight | Leaf lesion are long, irregular in shape, with wavy margins and are yellow to pale brown in color; streaks may extend length of leaf. | Severe disease can be expected when the mean temperature for December, January,and February is above 33°F. Cold winters (mean <32°F) reduce corn flea beetle populations. | Corn flea beetle feeding on leaves; bacterium overwinters in beetle. | Resistant hybrids; seed-applied insecticide to control flea beetle may be helpful. |
| Common rust | Reddish-brown, oblong pustules on leaves; rust-colored spores rub off on fingers. | Cool temperatures (60°F to 70°F) and high humidity. | Spores are wind blown into the area; new infections, causing spread within field, occur every 7 to 14 days. | Resistant hybrids; fungicides. |
| Eyespot | Small (1/8 to 3/8 inch) circular spots with tan to gray centers; margin of spot is brown to purple and commonly surrounded by a yellow halo. | Eyespot is common in no-till fields or fields with corn residues left on soil surface. Moderate temperatures, high humidity, and abundant rainfall. | Spores produced on residues are rain splashed or wind blown onto nearby seedlings. Spots appear 4 to 10 days after infection. | Resistant hybrids; clean tillage and/or crop rotation; fungicides. |
| Northern corn leaf blight | Large leaf lesions, generally to 1 in. by 2 to 6 in., grayish-green, later becoming tan to grayish black. | Favored by temperatures of 65°F to 78°F accompanied by heavy dews. | Fungus survives on corn residues and spores dispersed by wind. Spores are air-borne long distances. | Resistant hybrids; clean tillage of corn residues; crop rotation; fungicides. |
| Southerncorn leaf blight - race 0 | Small (1/4 x 1/2 to 1 in.), tan, oblong lesions are generally parallel-sided but sometimes are spindle-shaped. Lesions usually develop reddish-brown borders. | Favored by temperatures of 70°F to 90°F accompanied by heavy dews. | Fungus survives on corn residues, and spores are spread by wind and rain. | Resistant hybrids; clean tillage of corn residues; crop rotation; fungicides. |
| Northern leaf spot | Lesions are variable in size and shape; may be circular, oval, or linear and range from flecks up to 3/4 in. long; tan to brown in color. | Favored by warm, humid conditions with heavy dews. | Fungus survives on corn residues, and spores are spread by wind and rain. | Resistant hybrids; seldom prevalent enough to depress yields except on inbreds or no-till continuous corn, fungicides. |
| Anthracnose | Leaf spots are oval to elongate, tan and 1/4 to 3/4 in. long. Some have brown or orangish borders. On resistant hybrids, lesions are smaller and yellow to brown in color. Spore bodies with black spines can be seen with a hand lens. | Favored by normal to above normal rainfall and moderate to warm temperatures (80°F to 85°F). | Fungus survives on corn residues and spores are spread by splashing rain. | Resistant hybrids; crop rotation; clean tillage of corn residues; balanced soil fertility. |
| Yellow leaf blight | Leaf spots are oval to elongate, tan and 1/4 x 1/4 to 3/4 in., buff to tan colored, often with a darker border. Dark specks (pycnidia) can be detected in the lesion center with a hand lens. | Favored by cool, wet weather. Disease is more common in no-till fields with continuous corn. | Fungus survives on corn residues and some grassy weeds. Spores are spread by wind or splashing rain. | Resistant hybrids; clean tillage of corn residues; crop rotation; good weed control. |
| Holcus bacterial | Spots at first are dark green and water soaked, later turning brown or whitish with reddish-brown borders and are round, oval, or irregular in shape. | Warm temperature (75°F to 85°F), wet, windy weather early in season. | Bacteria survive on crop residues and are spread by splashing rain, blowing soil particles, and cultivation during heavy dews. | Resistant hybrids; clean tillage of corn residues; crop rotation. |
| Gray leaf spot | Leaf lesions are pale brown or gray, parallel-sided and 1/8 to 1/4 x 1/4 to 2 in. Usually occurring late in the season. | Warm, humid weather; July through September. | Fungus survives on crop residues and on barnyard grass and johnsongrass. Spread by wind and splashing rain. | Resistant hybrids; clean tillage of crop residues; crop rotation; fungicide application on susceptible hybrids. |
| Common smut | Galls form on all plant parts; first appear as shiny grayish green raised areas which enlarge forming gray galls containing black powdery spore masses. | Smut is favored by dry conditions and injuries caused by hail, machinery, etc. Excessive nitrogen increases susceptibility. | Smut spores overwinter on soil surface; infection caused by wind-blown spores. | Avoid mechanical injuries; use balanced soil fertility, resistant hybrids. |
| Crazy top | Excessive tillering, rolling of leaves; tassels may develop ears; proliferation of husks. | Disease develops where soils have been saturated for 24 to 48 hr. before plants reach the 4th leaf stage. | Fungus survives in soil; new infections from soil-borne spores. | Avoid planting in low, wet areas; improve soil drainage. |
| Maize dwarf mosaic | Mottling or mosaic of light and dark green in young leaves and slight shortening of internodes. | Primarily in river-bottom fields where johnsongrass is a problem. | Several species of aphids vector MDMV and transmit it from overwintering johnsongrass to corn. | Virus-tolerant hybrids; eradicate johnsongrass. |
| Maize chlorotic dwarf | Primary symptom is the presence of very fine chlorotic strips adjacent to the small veins on the underside of leaves. Older plants become yellowed and reddened with severe stunting. | Primarily in river bottom fields where johnsongrass is a problem. | A leafhopper transmits MCDV from overwintering johnsongrass to corn. | Virus-tolerant hybrids; eradicate johnsongrass. |
| Root rot | Small yellowish-brown areas on primary roots and later on secondary roots. Affected roots later become black and die. Plants may show wilting, stunting, and yellowing. | Severe root rot usually occurs in heavy soils that are poorly drained; saturated soil conditions early in the season favor root rot development. | Fungi that cause root rot persist in the soil. | Improve drainage; avoid tillage when too wet. |
| Nematodes | Feeding on roots can cause stunting, yellowing, and/or wilting. Roots are small with proliferation of secondary rootlets near tips of larger roots. Affected plants are usually in patches. | Corn is more prone to damage when young. Nematodes are generally more active in light sand soils that are well drained than in heavy clay soils. | Nematodes live in the soil and feed on numerous plant species. | Crop rotation; proper weed control. |
| Gibberella stalk rot | Sudden onset of grayish-green leaf color; lower stalk turns light tan; pith inside stalk becomes soft; pith has reddish or pinkish discoloration. | Stress; leaf diseases; insect feeding; extreme weather; unbalanced soil fertility; high plant populations. | Fungus survives on corn residues. | Hybrids with good standability and resistance to leaf blight; control insects; balanced fertility; proper plant populations; crop rotation; early harvest; incorporate crop residues. |
| Anthracnose stalk rot | Shiny black streaks, specks, or large blotches discolor the stalk surface; pith decays and turns brown. Stalks weaken and lodge. | Favored by high temperatures and extended periods of cloudy rainy weather. | Fungus survives on leaf and stalk debris left on the soil surface. Spores are spread by splashing rain. | Resistant hybrids; crop rotation; clean deep tillage of crop residues; balanced soil fertility. |
| Fusarium stalk rot | Lower internodes of stalk prematurely turn brown. Internodes soften and pith shreds. A light pink discoloration of pith may be evident; stalks weaken and lodge. | Present primarily in drier regions or during seasons of below normal rainfall. | Fungus survives on stalk residues. Spores are spread by wind or splashing rain. | Hybrids with good standability and resistance to leaf blight; control insects; balanced fertility; proper plant populations; crop rotation; early harvest; incorporate crop residues. |
| Diplodia stalk rot | Lower internodes become brown near the nodes; internal pith darkens and disintegrates; stalks weaken and lodge. Small black bodies (pycnidia) develop near nodes and scattered over internodes. | Excessive rainfall in late summer with warm temperatures extending into early fall. | Fungus survives on stalk residues. Spores are spread by wind or splashing rain. | Hybrids with good standability and resistance to leaf blight; control insects; balanced fertility; proper plant populations; crop rotation; early harvest; incorporate crop residues. |
| Diplodia ear rot | Thick white mold begins at base of ear, becomes grayish-brown over husks and kernels; ear may be shrunken; kernels appear glued to husks; infected ears are lightweight; small raised black fruiting bodies on moldy husks later in the season. | Wet weather and mild temperatures from late whorl through early ear development; corn borer injury can cause entry wound. | Fungus overwinters on corn residue; spores spread by splashing rain. | Plant resistant hybrids; crop rotation; fall tillage; dry harvested grain to 15% and below. |
| Gibberella ear rot | A conspicuous pink to reddish mold starting on the ear tip and progressing toward the base of the ear. | Average temperatures below 72°F and 7 or more days of rain during the 3-week period after silking. | Infection from wind-borne spores usually follows injury to the ear from corn borer, earworm, birds, etc. Fungus survives in soil on crop residues. | Resistant hybrids; ears that dry in a declined position and those well covered with husks generally have less ear rot. |
| Fusarium kernel rot | Pinkish or discolored caps of individual kernels, sometimes with a pinkish mold growth. | Warm wet weather 2 to 3 weeks after silking. | Infection from wind-borne spores usually follows injury to the ear from corn borer, earworm, birds, etc. Fungus survives in soil on crop residues. | Resistant hybrids; ears that dry in a declined position and those well covered with husks generally have less ear rot. |
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