Sheath blight is now present in a few Missouri rice fields, and it is causing some damage to plants. Fortunately, this disease is not spreading rapidly in these fields due to the recent dry weather. However, farmers should scout their rice fields weekly for this disease from internode elongation to beginning bloom or hire someone to do this to determine if their fields should be sprayed with a fungicide. Yield loss may be severe especially for susceptible varieties if this disease persists and eventually attacks the flag leaf and head.
Fungicides should be applied when the disease threshold is reached for the variety growing in the field. Stratego, Gem, Quadris, and Quilt 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
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° F. As the disease progresses, entire leaves may be killed and the disease may spread to rice heads. Damage due to this disease can range from partial infection of the lower leaves to premature plant death. When this 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 2009.
REVISED: August 2, 2012