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Entomologist on hunt for what’s bugging rice

When there’s something bugging rice farmers, a large segment of the world’s population is likely to find out.

Americans each eat about 20½ pounds of rice yearly. But globally, people annually eat about 126 pounds each. And insects are consuming rice, too.

One of the worst, the rice water weevil, is a southeast Texas native measuring less than a quarter-inch long. But its gray snout has made a big dent in the size and quality of global rice supplies.

A Texas researcher is making great strides — many of them by splashing through rice paddies to scour grassy pinnacles and seed heads with his net — in controlling the menace.

Key Points

• Rice is an important crop on the global scene.

• Rice water weevil devours much rice in Texas and world.

• Texas A&M scientist makes it his quest to wipe out weevil.


“I’m looking for ways to integrate a variety of treatments to manage pests efficiently and economically,” says Michael “Mo” Way, Texas AgriLife Research entomologist at Beaumont, who has been working with rice and soybeans there since 1982.

Rice water weevils are among the most serious pests in causing lower yields and grain quality, Way says. And they don’t just stop in Texas. The weevils have become a global pest — making it to California by the 1950s, to Japan in the 1970s, then China, Taiwan and, more recently, Italy.

In Texas, farmers can lose 500 to 1,000 pounds per acre as this weevil swims, crawls and flies through the field, laying eggs underwater so the larvae can grow by gnawing on rice plant roots, the research states.

Way was patient in this quest to see no weevil. He spent six years sweeping through fields, looking for water weevil damage to determine the level justified for a farmer to spend money controlling the pest.

Farmers have been referring to old data, he says. Many new rice varieties are being grown with newer cultural methods, and it was not apparent whether these changes had really made any difference on rice weevil control.

Real world

Armed with many seasons of field data from test areas grown like true farm situations, Way and then graduate-student Luis Espino compared protected vs. unprotected plots with those planted on a variety of dates. The protected were treated with various insecticides.

“What we found is that if farmers plant during the optimum planting window, then they can expect the greatest yield losses due to water weevil,” he says. “And since we don’t recommend planting outside that optimum time, it behooves them to control for the weevil.

“Usually, our highest-management-level farmers plant during that optimum time — from the end of March to mid-April — and that enables them to produce a ratoon or second crop as well,” he adds. “So it makes good economic sense to control the weevil.”

To sample for weevils, Way and team take a 4-by-4-inch plug that contains about three plants, plus the soil around the roots.

“For every one larva per core, yield is reduced about 1%,” Way says. “So the economic injury levels [number of insects it takes to cause significant loss] are very low — much lower than we thought.”

Control usually means an insecticide, Way notes. But scientists also are developing products that are not as toxic to the environment as in the past.

“One of these is a seed treatment with Rynaxypyr, a chemical that is far less toxic to mammals and wildlife than previous compounds,” Way notes. “Reports from the field this year, where this product was used, are very, very encouraging.”

Because seed treatment is a preventative measure, it has to be applied to seed before planting. So Way recommends farmers rely on their field history with weevils. “Certain areas are more prone to water weevil damage,” he says.

Farmers also should make the decision to use seed treatment based on planting date, variety, seeding rate, typical plant stand and time of flood.

“Based on these parameters, they can decide for themselves whether they will need the seed treatment,” Way suggests.

Way’s study also notes a couple of secondary benefits from seed treatment — all of the chemical stays with the seed rather than drifts in the air, and it has the ability to control other rice pests, such as stalk borer, fall armyworm and South American rice miner.

“So this reduces the pesticide load in the environment,” he says. “And farmers have another tool in their toolbox.”

And people have more rice on their plates.

Phillips is with Texas A&M Agriculture Communications, College Station.

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SEE NO WEEVIL: Mo Way, Texas AgriLife Research entomologist, examines a rice plant in his lab.

This article published in the February, 2010 edition of THE FARMER-STOCKMAN.

All rights reserved. Copyright Farm Progress Cos. 2010.