Encyclopedia - Corn

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Head Smut of Corn

Head smut of corn forms on the tassels and ears, galls are at first covered with a thin layer of tissue that breaks open to expose the black spore masses and threadlike remains of the vascular bundles. Leaf-like proliferations develop on the tassel and ears. Ears may be aborted and replaced with a proliferation of leafy tissue. Plants als... Read More

Holcus Leaf Spot of Corn

Holcus leaf spot usually does not cause major losses. Leaf spots are initially oval to irregular, dark green, water-soaked at the margins, and may have a light brown border. Later, lesions dry out and turn light tan, usually without a border. The dry lesions have a papery texture. Holcus leaf spo... Read More

Maize Dwarf Mosaic of Corn

Maize dwarf mosaic is caused by the Maize dwarf mosaic virus. Infected plants have a stippled (small, discolored specks) mottle or mosaic of light and dark green that may develop into narrow streaks on the youngest leaves. There may be a shortening of internodes causing a stunted, bunchy appearance of the plant. As plants mature and temperatures rise, mosaic symptoms oft... Read More

Nematodes that Feed on Corn

Multiple plant-parasitic nematodes feed on corn roots. Although prevalent, they rarely cause economic damage. Symptoms of nematode damage can occur any time during the season and include poor or uneven stands, chlorosis, stunting, and small or poorly filled ears. Often, symptoms occur... Read More

Northern Corn Leaf Blight of Corn

Northern corn leaf blight (NCLB) symptoms usually appear first on the lower leaves. Leaf lesions are long (1 to 6 inches) and elliptical, gray-green at first but then turn pale gray or tan. Under moist conditions, dark gray spores are produced, usually on the lower leaf surface, which give lesions a "dirty" gray ap... Read More

Northern Corn Leaf Spot of Corn

Northern corn leaf spot, also known as Carbonum leaf spot, is occasionally seen in the lower canopy during periods of high humidity and moderate temperatures. There are five known races of this fungus. Races 2 and 3 are the most common in the Midwest. Race 2 causes oblong, somewhat rectangular, brown spots (¼ to ½ by 1... Read More

Penicillium Ear Rot of Corn

Penicillium ear rot of corn is characterized by green or blue-green powdery mold growing between kernels, usually at the tip of the ear. Infected kernels can appear bleached or streaked. This rot occurs primarily on ears damaged mechanically or by insects, and it is more common in non-Bt corn because of the greater potential for insect... Read More

Physoderma Brown Spot of Corn

Symptoms of Physoderma brown spot usually appear on mid-canopy leaves. Leaf lesions are numerous, very small (approximately ¼ inch in diameter), round to oval, yellowish to brown in color, and usually occur in broad bands across the leaf. Alternating bands of infected and noninfected tissues are common.... Read More

Physoderma Stalk Rot of Corn

Physoderma stalk rot is caused by the same fungal pathogen that causes Physoderma brown spot. It is not usually an economic problem. Stalk rot symptoms are first noticed when plants break at the first or second node. These nodes are black and some pith rot may be present. Infected nodes snap easily if gently pushed. Microscopic examination of symptom... Read More

Pythium Stalk Rot of Corn

Pythium stalk rot of corn can occur any time during the season, particularly if conditions are very wet. It causes decay of the first internode above the soil. The rind and the pith become soft, brown, and water-soaked. The stalk typically twists and falls over, but the plant may remain green for several weeks because the vascu... Read More

Root Rots of Corn

Corn root rots are very common and are caused by several soilborne pathogens. Root rots occur to some extent in every field, causing economic losses under wet conditions. Aboveground symptoms include stunting, uneven growth, chlorosis, small or poorly filled ears, or wilting. In saturated conditions, effects of root rot are difficult... Read More

Seed Decay and Seedling Blight of Corn

Many pathogens cause seed decay and seedling blight of corn. The first symptom may be an area of the field with poor or no stand. Decayed seeds are very soft and may be covered with fuzzy fungal growth; seeds can be difficult to find if badly rotted. Postemergence damping off appears as yellowing a... Read More

Southern Corn Leaf Blight of Corn

The pathogen that causes southern corn leaf blight has two races. Race O normally attacks only leaves. Lesions are tan, somewhat rectangular in shape, and have reddish-brown margins. Race T attacks leaves, husks, stalks, leaf sheaths, shanks, ears, and cobs. Race T lesions are rectangular to elliptical (¼ to ½ inch wide by... Read More

Southern Rust of Corn

Although southern rust is generally considered a tropical disease, it can occur in important corn production areas of the United States and Canada. Symptoms are similar to common rust, but pustules are smaller and occur almost exclusively on the upper leaf surface. Pustules are usually circular or oval, very numerous, a... Read More

Stewart's Disease of Corn

Stewart's disease lesions spread from flea beetle feeding scars (a tiny scratch on the leaf) and are initially pale green to yellow streaks, later becoming brown as tissue dies. The margins of the streaks are usually wavy but generally follow leaf veins. If... Read More

Tar Spot of Corn

Tar spot can cause severe yield loss on susceptible hybrids when conditions are favorable for disease. Tar spot appears as small, raised, black spots scattered across the upper and lower leaf surfaces. These spots are ascomatum (fungal fruiting structures). If viewed under the microscope, hundreds of sausage-shaped asci (spore cases)... Read More

Trichoderma Ear Rot of Corn

Trichoderma ear rot of corn appears as dark green mold growing on or between kernels, often covering the entire ear. Kernels may sprout on the cob if disease is severe. It is primarily found on scattered plants under severe stress and is associated with injury to developing ears. Typically, it is not economically damaging. Grain sh... Read More