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Sorghum Diseases
William S. Gazaway, Extension Plant Pathologist
Paul L. Mask, Extension Agronomist
Diseases of grain sorghum reduce both seed quality and yield. Losses to disease have increased in recent years. Descriptions of the diseases found on grain sorghum are listed below.
Anthracnose
Anthracnose can be a serious problem in fields where grain sorghum has been grown continuously. This disease attacks both foliage and stalks. It forms red to maroon lesions with tan centers along the mid rib of lower leaves. As the lesions increase in size and number, affected leaves become severely blighted and die. Rapid blighting can occur during wet, humid weather. Stalk rot can be identified by the appearance of red to purple tissue on the stalk's surface and in its pith just below the seed head. Anthracnose develops most rapidly after flowering as the grain matures.
Zonate Leaf Spot
Zonate Leaf Spot is a common disease of grain sorghum that occurs primarily on the lower leaves and leaf sheaths. Spots on the leaves are circular, reddish-purple bands separated by tan-colored areas which form a concentric or zonate pattern ranging up to several inches in diameter. This disease develops mainly during wet weather. It rarely has a significant effect on grain quality or yield.
Rough Spot
Rough Spot develops as elliptical, reddish lesions with well defined margins on the leaves. Leaf spots are rough to the touch due to hard, raised, black fruiting bodies of the causal fungus. The spots merge, killing areas of the leaf. This disease is common but is rarely a serious problem.
Gray Leaf Spot
Gray Leaf Spot is a late-season disease of grain sorghum. Small red spots on the leaves enlarge into dark red to purple rectangular areas bordered by leaf veins which may merge to form elongated stripes. The spots produce a gray cast as the causal fungus sporulates during moist, humid weather.
Maize Dwarf MosaicVirus (MDMV)
Maize Dwarf MosaicVirus (MDMV) is a disease of corn and grain sorghum spread by aphids. This disease forms a mosaic of fine, yellow-green and dark green streaks that are most apparent on the younger leaves in the whorl. Red leaf, characterized by red streaks, may appear on the foliage of some sorghum varieties exposed to cool night temperatures. The disease is most common on early grain sorghum planted in johnsongrass-infested fields.
Fusarium Head Mold
Fusarium Head Mold occurs following periods of humid, hot weather at or shortly after bloom. The fungus invades the panicles and the rachis of the seed head and then the seed stalk. Red to purple spots are found on the diseased panicles and rachis. A white to pink cotton-like growth may be seen on infected seed heads. Tissues of the infected seed stalk are a solid dark red. Diseased stalks may lodge. Swine are highly sensitive to toxins produced by causal fungus on diseased grain.
Charcoal Rot
Charcoal Rot develops during times of severe drought. Plants are infected at the soil line as the grain begins to mature. Soft tissues of the pith quickly disintegrate, leaving only the string-like vascular bundles. Extremely small black fungal bodies cover the vascular bundles, giving the pith its characteristic salt and pepper appearance. Diseased plants usually lodge.
Nematodes
Nematodes feed on roots of grain sorghum. Plants attacked by nematodes are chlorotic, slow growing, and stunted. Symptoms resemble those of nutritional or moisture stress. Roots damaged by nematodes are thickened, stubby, and discolored. Nematodes can be accurately diagnosed only by nematode analysis of soil samples from the affected area. See Circular ANR-0114, "Collecting Soil And Root Samples For Nematode Analysis," for further information on sampling procedures.
