Cercospora remains slight threat for 2009

Frances Gould, Schultz, Bruce  |  6/25/2009 8:08:25 PM

LSU AgCenter pathologist Dr. Don Groth advises farmers at the Southwest Louisiana Field Day on strategies for treating and preventing diseases in their rice crops. (Photo by Bruce Schultz)

The threat of Cercospora will remain a slight possibility for the 2009 crop, even though it hasn’t been a widespread problem since 2006, according to Dr. Don Groth, LSU AgCenter pathologist at the Rice Research Station.

Groth said he received only two reports of severe pressure from this disease in commercial fields in 2008, and he had no success at getting the disease to emerge on his research plots at the station.

"Even on the most susceptible variety (Cheniere) I grew here on the station, it didn’t develop," he said.

The 2006 growing season was prime for Cercospora because of the preceding warm, wet winter, which allowed the fungus to overwinter, and the following wet summer weather. Even more, the proper fungicide choices were not established then, Groth said.

That hurdle has been overcome, however, and the LSU AgCenter researcher says using Stratego and Quilt is a good strategy to treat rice for sheath blight – with the added benefit of protection against Cercospora. Both materials have propiconazole to fight Cercospora and strobilurin for sheath blight.

Timing for application is best at a 4- to 6-inch panicle in the boot stage, he said, when it provides good treatment for Cercospera and sheath blight. "It’s a good time to control both diseases," he said.

Groth said he is concerned that he has seen more blast in 2008, adding, "That has us worried."

Some farmers choose to delay the flood until tillering to control water costs, Groth said, but that could open the door for blast if soil conditions are dry. "Flooding the field is the best control method for leaf blast," Groth cautioned.

Groth said blast is adapting to some varieties, particularly Cocodrie and CL161, and could be more of a problem with CL151.

Sandy soil, fields surrounded by trees and late planting can promote blast development, he said.

Strobilurin fungicides have activity against blast when applied at 50-70 percent heading, he said, but the late timing could diminish effectiveness against Cercospora and sheath blight.

"However, you treat for your worst problem and that would be blast in these situations," Groth stressed.

The LSU AgCenter scientist said he is testing new versions of Stratego and Quilt that are tailored for rice. "The new formulations have the proper ratio of propiconazole and strobilins for rice, and they are more effective than the current formulations we have," he said. –Bruce Schultz

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