Entomologist Dr. Michael Stout checks a sticky trap for rice water weevils. Stout is trying to identify replacements for Icon, which was found to be toxic to crawfish.

Distributed 04/23/04

Rice farmers concerned about the loss of the seed treatment Icon have reasons to be hopeful.

LSU AgCenter entomologist Dr. Michael Stout is studying three chemicals that could be used as seed treatment replacements for Icon to fight rice water weevils.

In addition, Stout is studying two proposed granular chemicals aimed at the weevils.

The projects, under way at the LSU AgCenter Rice Research Station near Crowley, are funded by the Louisiana Rice Research Board.

Among those efforts, two new chemicals are being tested for Syngenta. One seed treatment is thiomethoxan, Stout said, and the other is a proprietary chemical being kept under wraps.

"I am really excited about this proprietary chemical, because it worked really well last year," he said.

The LSU AgCenter scientist said he’s not sure if the proprietary formula will be toxic to crawfish. A class-action lawsuit was settled recently by crawfish farmers who sued Aventis, maker of Icon, and the litigation resulted in a $45 million settlement with Bayer CropScience, which acquired Aventis’ pesticide division.

Bayer announced earlier this year it would no longer make Icon because of lagging sales, but that remaining stocks would continue to be sold until they are depleted.

Karate also is being tested a second year as a seed treatment, although last year’s results were not promising, Stout said.

Weevil larvae feed on the roots of aquatic plants, not just rice, Stout said. But in the case of rice, yield is reduced considerably.

Stout said he is testing two granular products for application after flooding, and they seep into the soil to kill weevil larvae. They would fill a void created by removal of the granular chemical Furadan in 1997, he said.

Little is known about the basic biology of weevils, Stout said. It’s possible that Furadan was so effective that entomologists didn’t need to research weevils, he said.

Currently, foliar pyrethroid chemicals, such as Karate, Mustang Max, Prolex and Proaxis, are approved for application to kill adult weevils before they lay eggs in rice fields.

"It makes timing critical for those products," Stout explained.

Prolex and Proaxis recently were approved for rice farming, and they are expected to be available in May.

Stout said many farmers chose the foliar chemicals because they have been cheaper than Icon.

Dr. Boris Castro, also an LSU AgCenter entomologist, said he fears weevils could become resistant to pyrethroids.

In addition, the foliar chemicals can drift to nearby crawfish ponds and devastate a crop of the crustaceans, Stout said, but a granular chemical wouldn’t be as much of a problem.

Stout has an ongoing project, funded by the U.S. Department of Agriculture, to find out exactly what attracts weevils to a rice field.

Many farmers already have been hit with adult weevils in their fields this year, but so far at the LSU AgCenter’s Rice Research Station near Crowley, few weevils have been found in the fields and in traps.

Stout said he suspects cool, breezy weather may be keeping the weevils in their wintering areas – usually wooded areas with plenty of leaf litter for food and shelter.

Recent windy conditions have made it difficult to find weevils in flooded fields, Stout said, because they usually swim to the bottom when strong breezes blow across the water.

One project that Stout has under way is aimed at determining whether planting early helps plants better endure a weevil infestation. Test plots in that study are planted two weeks apart.

"That is a pretty easy management practice," Stout said.