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Colder temperatures delay disease incidence in South Louisiana rice

Last winter’s colder-than-normal temperatures may have been uncomfortable at the time, but they appear to have resulted in less disease pressure in Louisiana rice fields this summer.

“We’re having a fairly light disease year compared to normal,” says the Rice Research Station’s Don Groth. “We had a very cold winter that killed a lot of the stubble crop that grows down here. Pathogens usually overwinter on that stubble crop.

“We’re just now seeing some blast and cerscospera starting to develop, which is much later in the season than normal. Sheath blight is in some fields, but in others you can’t find any sheath blight. But where it is it is growing very rapidly. These hot humid conditions are favorable for its development.”

Groth, plant pathologist at the LSU AgCenter station, was one of several speakers at the Station’s annual field day June 25. The traditional tours during the field day, which annually attracts several hundred rice producers and industry specialists, had to be moved indoors because of the threat of rain for only the second time in at least 30 years.

Bacterial panicle blight, which has been a problem in some rice-growing states some years, has been absent, Groth noted. “Unless it gets a lot hotter than it already is, we’re not going to see much. We’re not anticipating a lot of bacterial panicle blight.

“Where we have sheath blight and blast, we’re recommending farmers go ahead and spray because the potential is they could develop to eipidemic levels in a short period of time, and fungicides are justified in those conditions.”

Groth talked about the rhizoctonia solani or sheath blight pathogens that have developed resistance to the strobilurin fungicides, such as Quadris, Quilt, Stratego. “Basically, we have lost the strobilurin technology in these resistance areas. They have no activity against this fungus.”

Growers should be alert to areas in the field that aren’t being controlled when those fungicides are applied. Because of the potentisal for resistance, producers should switch to other modes of action such as Sercadis, a new fungicide that received federal registration for application on sheath blight in rice earlier this year.

“We also have Convoy and the propiconazoles have different activity,” he noted. “But the idea is to start using some of these alternate fungicides before you have resistance because if you lose the strobilurins, you’ve lost such a major tool. We’re not going to recover from that.”

Cercospora is another disease that should be on growers’ radar. After favorable environmental conditions – and a lack of effective fungicides – contributed to a major outbreak of the disease in 2006, farmers have had to include the disease on their scouting lists.

To read more about cercospora, visit



TAGS: Management
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