It is favored by warm, humid weather. Yield losses can be as high as 36 percent. Spots develop on leaves and leaf sheaths at all stages of plant development. Lesions are round to oblong, with a definite margin varying in size. The spots may continue to enlarge and coalesce to form blotches that cover large areas of the leaf.
Older lesions are olive-colored because of sporulation of the fungus.
Spot blotch is best controlled by resistant varieties. The use of pathogen-free seed or a fungicide seed treatment can reduce seedborne or soilborne inoculum. Powdery Mildew Powdery mildew is caused by the fungus Erysiphe graminis . The pathogen attacks barley, rye, and triticale. With fall rains, spores are released from cleistothecia, and they infect nearby plants.