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Sheath blight is present in a few Missouri rice fields, and it is causing damage. It is not spreading rapidly in these fields due to the dry weather. However, farmers should scout their rice fields weekly for this disease from internode elongation to beginning bloom to determine if the field should be sprayed with a fungicide. Yield loss may be severe if this disease persists and eventually attacks the flag leaf and head. Varieties such as Clearfield 161, Cocodrie, and Cybonnet are very susceptible to this disease; Wells is susceptible; Francis, XP723, and XP730 are moderately susceptible; and XP710 is moderately resistant.

Fungicides should be applied when the disease threshold is reached for the variety growing in the field. Stratego, Gem, Quadris, Quilt, and Moncut are labeled fungicides for control of this disease. University of Missouri Extension Regional Agronomist can supply information about sheath blight thresholds, or you can call me at the Delta Center. More information about sheath blight identification, control, and thresholds for treatment of fields with fungicides is available at aes.missouri.edu/delta/muguide/mp646.stm

Sheath blight lesions on rice stems. Photo courtesy of Allen Wrather.

Here's the situation. Sheath blight is caused by a fungus that most often infects rice plants soon after the flood is applied. Sheath blight lesions develop first on the stem near the water line. These lesions are circular to oblong (1 inch long and 0.5 inch wide), with grayish-white centers and purple-brown borders. Infection and spread of the disease is more severe when humidity is high, rain is frequent, and average daily temperatures are around 82 degrees. As the disease progresses, entire leaves may be killed and the disease may spread to rice heads. Damage can range from partial infection of the lower leaves to premature plant death. When the disease is severe, yield and milling quality of kernels can be reduced.

Following these suggested procedures will give rice farmers a better chance to produce high yields and profit in 2007.

Allen Wrather, Professor
Division of Plant Sciences