Zonate leaf spot of millet is caused by the soil-borne fungus Gloeocercospora sorghi. Contaminated seed or soil-borne sclerotia (dormant resting structures) initiate epidemics during warm, wet weather. Spores (conidia) produced in lesions are disseminated within and between fields by wind and splashing water. The pathogen likely survives in the soil for several years in the absence of a host.
Zonate leaf spot symptoms initially appear as water-soaked spots that later develop tan centers with dark brown borders. Lesions enlarge with time, and become somewhat circular in shape and cover half or more of the leaf width. Concentric and alternating dark brown and light tan rings are often apparent, but may be absent from narrow-leafed varieties. During moist weather, small, salmon-colored spore masses are visible lesions when viewed under magnification. Black sclerotia are apparent on dead tissues.
No biological control strategies have been developed for zonate leaf spot.
Cultural controls are not necessary for zonate leaf spot because the disease is of minor concern in the High Plains region. Crop rotations of four-years or longer, avoidance of overhead irrigation, and thorough incorporation of crop residues may reduce disease incidence and severity, should it become a problem.
Chemical controls are not available.
Categories: Millet, Disease, Zonate Leaf Spot
Date: 03/22/2005