Managing disease can be a frustrating proposition. This Guide can help you identify which disease is damaging your crop.
American Wheat Striate Mosaic Virus
The initial symptoms on susceptible varieties are very thin white to yellow striations or lines on the undersurface of the lower leaves.
Anthracnose Stalk Rot
Water-soaked areas on the surface of the lower internodes, developing brownish linear streaks, turning black later in the season, larger oval black areas may develop.
Common Bunt (Stinking Smut)
Infected heads remain green longer than uninfected heads, glumes may be spread apart, infected seeds appear dark, internal tissues replaced by masses of black fungal spores.
Partial to complete replacement of the normal tassel by a large, bushy mass of small leaves. No pollen is produced.
Affected leaves are covered with numerous small round spots. Spots are ~ 1/8 inch in diameter, oval to circular and appear water-soaked.
Fusarium Stalk Rot
The leaves turn from a healthy green color to a dull green and the lower stalk becomes yellowed..
Gibberella Stalk Rot
Stalks that are split open have a disintegrated pith with pink discoloration. The vascular bundles will appear reddish in color.
Gray Leaf Spot
Early lesion produced on the corn leaves by Cercospora zeae-maydis are yellow to tan in color and look similar to those produced by other diseases except they have a faint watery halo which can be seen when held up to the light.
The disease cannot be easily detected in plants growing in the field: the grain must be removed from the head and examined.
Infected heads are blackened with a dry, powdery mass of fungal spores. Entire seed is replaced by black fungal spores. These spores are soon blown away, leaving the rachis of the head bare.
Maize Dwarf Mosaic
Early infection results in chlorotic spots or flecks that elongate in young leaves in the whorl. Flecks merge into chlorotic streaks along the leaves.
Northern Leaf Spot
Narrow, small, linear to oval shaped leaf lesions Race 1 lesions are tan, oval to circular with concentric zones and are commonly 1/2 inch in width and 1 inch in length.
Rhizoctonia Spring Blight
Large, irregular lesions on dormant leaves. If plants are dormant or stressed after infection, the fungus may develop into crown tissue and plants may die.
The seed rots prior to germination.
Southern Corn Rust
Similar to common rust except pustules occur almost exclusively on the upper leaf surface, rarely on lower.
Stewart's Bacterial Disease
his disease has two phases and primarily is a problem on sweet corn and susceptible inbreds, although resistant hybrids may be affected if flea beetle populations are very high in the spring.
Long stripes of small yellowish orange pustules appear on the leaves. These pustules consist of masses of rust spores.
Tan-brown, flecks on upper and lower leaf surfaces expanding to blotches 12 mm long (often with yellow borders).
Wheat Spindle Streak Mosaic Virus
Yellow-green mottling, dashes, and streaks on lower leaves. Reddish streaking and necrosis at leaf tips sometimes occurs.
Anthracnose Leaf Blight
Anthracnose of corn may appear as a leaf blight, stalk-rot, top-kill of the stalk, and kernel rot. But most damage results from the stalk rot and leaf blight phases.
Barley Yellow Dwarf Virus
The primary symptoms of the disease are stunting, and leaf tip yellowing, reddening, or purpling of leaf tips.
Common Corn Rust
Initial symptoms are chlorotic flecks on leaf surfaces. Flecks develop into oval to elongate reddish brown powdery pustules on upper and lower leaf surfaces.
Diplodia Stalk Rot
Leaves turn grayish-green and eventually brown. Dark brown lesions extend in either direction from the node. Pith is disintegrated and discolored, stalks break easily.
Fusarium Ear Rot
Seldom involves whole ear, rot usually occurs at tip of ear or in scattered areas on ear, color of mold around infected kernels varies from white to pink to reddish brown.
Gibberella Ear Rot
Reddish or pink mold that usually starts at the tip of the ear. Husks may adhere tightly to the ear (hybrid dependent).
Glume Blotch Complex
The initial symptoms are small brown spots on the glumes (outer chaff), lemmas (inner chaff) and awns. The spots are most common at the tips of the chaff parts.
High Plains Mosaic Pathogen
Severe stunting, yellowing, and a strong mosaic. Discoloration is variable. Some leaves have green and yellow stripes at the leaf tips similar to wheat streak mosaic.
Leaf rust causes very small (about 1/32 inch long by 1/64 inch wide), orange pustules that erupt through the leaf surface. In some cases, pustules are surrounded by a narrow yellow or white halo.
Maize Chlorotic Dwarf
MCD symptoms include yellowing of youngest leaves in the whorl and a distinct fine yellow striping, or vein clearing of the smallest veins visible between the larger veins.
Northern Corn Leaf Blight
Long cigar-shaped gray-green or tan lesions. As the disease develops, the lesions spread to all leafy structures, including the husks.
White or gray-brown powdery or cottony patches of mycelium (fungal threads) on the upper surface of lower leaves.
Scab (Fusarium Head Blight)
Spikelets appear bleached often with a pale pink tint, tombstone kernels, seed light weight, sometimes infected spikelets are barren and can produce mycotoxin, seedling blight.
Southern Corn Leaf Blight
Corn growing areas of the world. Infections are most serious in warm, temperate and tropical areas.
Stem rust causes dark orange pustules on the stems and also on the leaves. It is similar to leaf rust, but leaf rust does not attack the stems.
Strawbreaker (foot rot)
Early spring symptoms of strawbreaker are elliptical or eye-shaped lesions on the leaf sheaths near the soil line.
Take-all Root Rot
Detectable around jointing time, affected plants are stunted and yellow compared to healthy plants.
Wheat Soilborne Mosaic Virus
Mild green to yellow mosaic with parallel streaks on lower leaves. Yellow-green mottling, dashes, and streaks.
Wheat Streak Mosaic Virus
Initial spring symptoms of wheat streak mosaic virus usually show up in April on edges of fields near volunteer wheat.