The current hot, dry weather in southeast Missouri, northeast Arkansas, and west Tennessee will slow the development of rice blast, but this weather pattern may change. Rice farmers in these areas should scout their rice fields or hire a professional to scout their fields for blast from boot stage until head emergence is complete. If symptoms are present on leaves at boot stage, growers should take action to manage this disease.
If blast symptoms are present on leaves at the split boot stage and the weather is predicted to be cloudy with frequent rains and heavy dew for the next 10 days, rice may be treated with a fungicide for protection against this disease developing on the rice heads. Fungicides should be applied for blast management when panicles begin to emerge from the boot (when the heads of 50% of the main tillers have emerged ¼ inch from the boot) and again 7-10 days later when panicle emergence is 75-90% complete (the heads of 50% of the main tillers have all emerged but for ¼ inch). Farmers may use Quadris, Gem, Stratego, Quilt, and Quilt Xcel for the first application and Quadris or Gem for the second application.
Blast is caused by a fungus that can infect leaves, nodes and panicles. Leaf spots are typically diamond shaped with a brown to red-brown border and a gray-white center. They may be 0.5 inches long and 0.25 inches wide, but size will vary. Yield loss will be severe when the disease develops on the nodes just below the head. This phase of the disease is called neck blast or rotten neck. The infected nodes will be discolored, the heads on these plants will turn white, and grain will not develop or develop poorly.
University Extension Regional Agronomists can supply more information about blast, or you can call me at the Delta Center. More information about rice blast is also available at the Delta Center Web Page, http://aes.missouri.edu/delta.
Following these suggested procedures will give rice farmers a better chance to produce high yields and profits during 2010.
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REVISED: February 29, 2012