Soybean podworm starts to show up in Louisiana fields

Richard Bogren, Kerns, David L.  |  7/16/2012 8:59:09 PM

News Release Distributed 07/16/12

An uncommon pest showing up in Louisiana soybean fields is not yet much of a problem for farmers but is causing concern for LSU AgCenter entomologists.

It’s the soybean podworm, the same pest that’s called the corn earworm in corn fields or bollworm in cotton fields, said LSU AgCenter entomologist David Kerns.

“They can show up almost any time from newly emerged seedlings to those in later reproductive stages,” Kerns said of the podworm. “But it is primarily a flower, pod and seed feeder.”

The pest generally avoids feeding on leaves and attacks the fruiting structures. The result in a soybean field can be empty pods and accompanying yield reductions, he said.

“It is becoming more common with increasing soybean acreage,” Kerns said.

Kerns is working collaboratively with scientists in Mississippi and Arkansas to learn more about the soybean podworm and establish action thresholds for treating for the pest when it appears.

In other soybean work, Kerns is participating in a study to evaluate new soybean varieties that express Bt proteins and are resistant to some foliage-feeding caterpillars.

“This technology is in the stages of early development,” Kerns said.

Bt corn is on Kerns’ radar with the advent of “refuge-in-the-bag” seed. Some seed companies have received registration from the Environmental Protection Agency to mix non-Bt corn with Bt corn in the same bag. So, instead of having to plant a separate area of the field to a refuge non-Bt crop, this “refuge” is randomly scattered among Bt corn plants, Kerns said.

In this system a small portion of the plants – generally about five percent – are non-Bt. This allows farmers to comply with insect resistance management guidelines without having to plant blocks of non-Bt corn on their farms.

Current EPA policy requires corn growers to maintain a percentage of their production acres in non-Bt corn. The corn stalk-boring insects and corn rootworms that feed in those non-Bt plants will maintain susceptibility to Bt. Then, when they mate with insects that survived feeding on Bt corn, the offspring will maintain genetic susceptibility to Bt.

He’s investigating how effective the refuge-in-a-bag corn is in Louisiana.

Spider mites have become a new pest of corn in Louisiana, Kerns said. “We don’t know the damage potential of this insect, and we haven’t developed any control tactics.”

He’s evaluating miticides as well as the interaction between fungicides and spider mites.

Spider mite populations can be suppressed naturally by certain fungi, Kerns said. But using fungicides for disease management in corn may suppress those fungi that infect and kill spider mites.

“Those beneficial fungi could be taken out of the picture if they’re eliminated as a result of controlling other plant disease fungi,” he said.

Kerns also is evaluating the economic benefits of controlling earworms in corn. It’s possible, he said, that allowing some earworm damage may be more cost-effective than applying a pesticide.

“We want to see how much yield increase we get by controlling corn earworms that mainly feed on the tips of the ears,” he said.

Rick Bogren

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