Rice water weevil celebrates dubious anniversary in California

There were no balloons, parades or cheers when Larry Godfrey, University of California, Davis, rice research entomologist, pointed out the rice water weevil was probably celebrating its 50th anniversary this season as a significant pest in California.

The first publication on the rice water weevil in California was in 1958, he told attendees at the Rice Experiment Station Field Day in Biggs, Calif. Since its debut, the rice water weevil has become a persistent problem throughout the years, fading in and out on a cyclical basis, but always giving growers a cause for concern.

“The rice water weevil flight this year was fairly spread out,” Godfrey says. “We’ve had other years where we’ve had just a two or three day period when most of the weevils were flying,” This year, Godfrey said there was a flight in early April; another peak flight about April 25; and another one from about May 2 to May 16. “If you had rice that was flooded during one of those times I would guess you had a pretty severe infestation.”

In terms of weevil numbers, they were about the same this season as in 2007, Godfrey says. “In 2006 and 2007 we were in an upswing in terms of the number of weevils. In 2008 the numbers were about the same as 2007, so maybe we’ve peaked out.”

Among the materials that are registered now – Dimilin, Mustang Max and Warrior – all are still working well, according to Godfrey. “We’d like to work in some new materials and give growers some new options,” he says. “Some of the materials have some problems from a regulatory standpoint. So with that in mind we’re working with some experimental products.”

Trebon (etofenprox) is a product commercially available in the South under an emergency registration. It’s not yet available in California, although researchers have been evaluating it.

“In the South they use it primarily in environmentally sensitive areas close to crayfish ponds,” Godfrey says. “It works very well there, and we’re pursuing registration in California.”

Another experimental is the seed treatment Dermacor. It is also registered in the South under a Section 18.

“I worked with it in 2006 and 2007 here in California,” Godfrey says. “It didn’t work that well, but I think that there were possible incompatibilities with the Clorox seed soak. It seemed like that might have affected the activity of the product. When I left out the Clorox seed soak, it worked fine.”

Other experimentals include V10170 – a seed treatment from Valent. “I’ve worked with that one for a couple of years,” Godfrey says. “It’s active as a seed treatment, active as an in-the-water treatment and active as a soil applied, pre-applied treatment. It provides very good weevil control, even at lower rates.”

It’s a neonicitinoid, common in other California crops. “I think it has a lot of attributes and I’m hoping it’s something that we can put on a fast track for registration in California rice,” Godfrey says.

Some rice varieties are more susceptible to rice water weevil. “Varieties such as S-102 and Calmati – if they’re infested with rice water weevil even at low numbers – the yield loss is quite dramatic,” Godfrey says. “Other varieties, such as the medium grains – M-106 and M-202 – can have pretty high infestations of rice water weevil and the yield impact is very minimal. I’m not saying it’s due to resistance in the variety. The weevils are still there, but those two varieties are very vigorous so they just grow right through the infestation.”

Other invertebrate pests, such as tadpole shrimp, seem like they’re becoming an increasing problem. Researchers are also on the lookout for rice panicle mite which is a very severe pest in Asia and South America. It has also been identified in Texas, Louisiana and Arkansas.

“It’s a pest we certainly hope we don’t find in California,” Godfrey says.

TAGS: Rice
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