Warm winter likely set stage for blast epidemic

Frances Gould  |  10/3/2013 1:26:57 AM

A microscopic view reveals blast spores. The disease decreased yields for many south Louisiana rice farmers in 2012, and scientists believe the warm winter set the stage for the epidemic. (Photo by Dr. Don Groth)

Photo By: LSU AgCenter

Dr. Don Groth just thought he had seen bad years of blast disease. Then along came 2012.

"I learned a new respect for blast," Groth said.

The LSU AgCenter plant pathologist said the disease appeared earlier and more severe than he’s ever seen, and it threatened major varieties such as CL151.

"We knew they were susceptible, but we’ve been growing them for years, and they’ve never been affected like this," Groth said.

Groth surmises the warm winter allowed the disease to thrive throughout the offseason on rice and weeds that survived the mild temperatures.

"There was already a lot of blast when we started planting," he explained.

Those conditions set up the perfect disease triangle of a susceptible host, a virulent pathogen and a favorable environment. "This is exactly the same scenario we had in 2006 with Cercospora," Groth said.

The LSU AgCenter scientist said blast was especially bad at the Rice Research Station, and it became apparent on CL151.

"We saw the early blast in our fields here, and we were able to warn people," Groth said.

He said farmers were able to shift their emphasis from sheath blight to blast, spraying fungicides at the head ing stage instead of applying too early at boot or late boot stages.

Groth said the disease usually started on leaves and then moved up the plant as rotten-neck blast that killed panicles. "We even had some fields that didn’t have leaf blast that had rotten-neck blast," he said.

If there was a silver lining, Groth said that might have been that the heavy blast pressure helped with variety development, because the heavy disease occurrences gave breeders a good idea what rice lines are and aren’t blast resistant.

"We had big differences," he said. "It was not unusual to have 100 percent blast in one row next to a row with no blast."

Some plots had severe infestations of blast, sheath blight and bacterial panicle blight. "The material we planted late (May) was attacked by every disease imaginable," Groth said.

He said the new fungicide Sercadis worked well against sheath blight that had become resistant to fungicides. Groth also said work continues on several experimental fungicides and that he was encouraged by the results – although he can’t talk about those yet because of nondisclosure agreements regarding the potential new material.

"With this resistant sheath blight, we now have new materials being developed," he said.

(This article was published in the 2013 Louisiana Rice Research Board Annual Report.)

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Please click on the links above to go to the Rice Research Board Reports home page, to go to the 2012 report, and to go to the PDF version of the 2013 report.

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