Zonate leaf spot (Gloeocercospora sorghi) is a conspicuous disease of Sudangrass, Johnsongrass, and sorghums. It has been reported also on sugarcane, corn, and pearlmillet. The mature spots are large and composed of alternating bands of reddish-purple and tan or straw-colored tissue, forming a zonate pattern. Spots near the leaf margin are semicircular. Those nearer the center of the leaf are nearly circular with irregular, wavy margins. Black sclerotia of the fungus develop within the tissues of the older leaf lesions and the fungus spores are borne in salmon-colored gelatinous masses (sporodochia) in and around the necrotic areas. In some seasons the disease is rather common in the lower Mississippi Valley.

Rough spot (Ascochyta sorghina) attacks Sudangrass, Johnsongrass, and sorghums. It has round or oval spots, which are yellowish brown or reddish Purple and are covered with small black fruiting bodies. The bodies usually are so abundant that the affected areas feel rough when rubbed between the fingertips.

Gray leaf spot, caused by the fungus Cercospora sorghi, is found commonly on Sudangrass, Johnsongrass, and sorghums in the Gulf States. When small, the reddish-purple to tan spots areindistinguishable as from other leaf spots, they elongate they become covered with a grayish-white fuzz, composed of fungus conidiophores and conidia. The conidia, spread by wind and rain, cause new infections.

Sooty stripe, caused by Ramulispora sorghi, occurs in the Southern States on Sudangrass, Johnsongrass, and sorghums. Mature lesions are elongate-elliptical, have a straw-colored center surrounded by a purple border, and usually are covered by numerous black sclerotia. In moist weather, fungus spores are produced in light-pink, gelatinous masses (sporodochia) on the lesions. The sclerotia function primarily in overwintering the fungus and the conidia produced by them are the chief source of infection in the spring.

Rust, caused by Puccinia purpurea, frequently attacks Sudangrass, Johnsongrass, and sorghums in the humid Gulf States. It causes the leaves to dry and break off, thus reducing the forage value. Rust pustules occur on both the upper and lower surfaces of the leaf. They are covered at first by a brownish coating. This soon breaks open and allows the chestnut-brown rust spores to escape. Purplish-red or tan areas develop around the rust pustules and the functional efficiency of large areas of leaf tissue is eventually destroyed.

Nonparasitic leaf discoloration caused by environmental conditions or hereditary factors also occur commonly on Sudangrass, Johnsongrass, and sorghums in the South. These lesions lack bacterial exudate and show no evidence of fungus fruiting structures, which serves to differentiate them from the parasitic disorders I have discussed.

SEED TREATMENT and crop rotation help check the diseases of Sudangrass, but the most feasible control measure is the development of disease-resistant varieties.

Tift Sudan, a variety resistant to leaf blight, anthracnose, bacterial stripe, and bacterial streak, was developed through cooperative work by the Department of Agriculture and the Georgia Coastal Plain Experiment Station.

The origin and early testing of this improved variety is described by Glenn W. Burton in Georgia Circular 11, published in April 1943.

Tift Sudan has become popular in the South because of its disease resistance. Plant breeders use it in attempts to improve Sudangrass still more.

Pearlmillet is susceptible to three of the diseases that attack Sudangrass; bacterial spot, zonate leaf spot, and the leaf spot caused by Helminthosporium rostratum. Eyespot, caused by Helminthosporium sacchari, also occurs on pearl-millet. The fungus infects and blackens the seed and causes a conspicuous leaf spot. Species of Curvularia have also been reported from leaf spots and seed of pearlmillet.

A more common leaf disease than any of those is caused by a species of Cercospora, which had not been named in 1953. That fungus causes a small, circular to elliptical spot with gray center and reddish-brown border. Both the improved variety Starr and commercial pearlmillet are susceptible to it. The disease usually develops rather late in the summer, however, and so the damage is not great during the pasturing season.

HOWARD W. JOHNSON is a graduate of Ohio State University. He has a doctorate in plant pathology from the University of Minnesota. He has been engaged in work on diseases of forage crops since i93o. He is employed jointly by the division of forage crops and diseases and the Mississippi Agricultural Experiment Station with headquarters at the Delta Branch Experiment Station, Stoneville, Miss.