• Pest Type: Disease
• Crops Affected: Rice
• Scientific Name: Rhizoctonia solani

Symptoms
Young lesions are oblong, green-gray, about 1 cm long and appear water-soaked. They appear on sheaths near the water line, usually when plants are in the late tillering or early internode elongation stages. Lesions turn brown as they age, and grow to about 2-3 cm in length and 1 cm in width. The have an irregular purple-brown border. Advanced lesions on leaves turn light brown to white with darker margins. the entire leaf will usually die. Sclerotia appear on the outside of the stem, near infected tissue. They are white when youg and dark brown and loose when mature. Sheath blight can also infect the panicle, resulting in poorly filled grains. Sheath blight-infected rice field will show typical "blowout" pattern of disease development.

Disease Cycle
Sheath blight overwitners as sclerotia in soil or as mycelium in plant debris. These are the primary inoculum. Sclerotia is disseminated by water movement or in soil on farm equipment. At flood, sclerotia float to the surface and infect stems at the water line. Under favorable conditions, infection spreads rapidly via runner hyphae to upper leaves and adjacent plants. In fields with low disease levels, infection is spotty. It takes 6 days from infection until symptoms appear. Older plants, especially at late boot stage, appear to be the most susceptible. Hot, humid weather favors disease development. Optimum temperatures are 85-90 F during the day and 70-80 F at night, but temperatures above 95 F limit development. Optimum humidity is between 95-100%.