News Release Distributed 08/14/14

BATON ROUGE, La. – LSU AgCenter entomologist Jeff Davis is working with redbanded stink bugs to see which soybean varieties have resistance to what has become the crop’s worst insect pest.

Last year, the study used 10 different varieties. Six varieties showed as much as a 20-bushel difference with spraying, while four varieties showed little or no difference, Davis said. This year, the study is testing 20 varieties.

Davis also is studying the redbanded stink bug’s resistance to acephate.

“If we lose acephate, we’re not going to have anything that gives us more than five days of control,” he said.

The alternative is Endigo, but it tends to kill beneficial insects that control soybean loopers, increasing that pest’s population.

In another project, Davis is trying to determine whether harvest aids used in fields with heavy stink bug populations will cause the insect to feed heavily on seed pods, damaging the beans.

It’s possible that a farmer could justify mixing an insecticide with a harvest aid to prevent potential pod damage and to stop stink bugs from moving into an unharvested field, he said.

“I get asked questions about this issue every year, and we hope this study will provide some answers,” Davis said.

Another project is aimed at soybean loopers and whether they feed on the weed Palmer amaranth more readily than soybeans. He said results last year showed the insects preferred soybeans.

This year, the study is focusing on adult loopers to see if they are attracted to flowering Palmer amaranth more than soybeans.

David Kerns, LSU AgCenter entomologist at the Macon Ridge Research Station in Winnsboro, is looking at the efficacy of soybean seed treatments to see if the neonicotinoid seed treatments are worth the expense. “It takes a number of years to figure that out,” he said.

The project is a regional endeavor with researchers from Mississippi, Tennessee and Arkansas.

The seed treatments are aimed at thrips and below-ground pests such as grubs. Kerns said the seed treatments sometimes also seem to promote an unexpected yield boost for no apparent reason.

Another of Kerns’ projects involves the economic threshold for spraying for bollworms in soybeans. A cage project is being used to determine a correlation between bollworm populations and yield effects.

“Depending on the stage of a soybean plant and the size of the bollworms, the amount of damage they cause will vary greatly," he said. “We’re still in the early stages of pulling this data together.”

Healthy soybean plants can compensate and develop new pods after bollworms have taken their toll on existing pods, but stressed or matured plants may not be able to do that, Kerns said.

This project also is in collaboration with researchers in other states.

A new soybean pest, the kudzu bug, which made its first appearance in Louisiana in 2013, also is on Kerns’ radar. Higher numbers of the insect have been reported in 2014 in northeast Louisiana. “Next year, we should have an even higher number,” he said.

The threshold for spraying for the insect is an average of one immature bug for every net sweep, he said. Yields may be reduced as much as 60 percent from kudzu bug feeding.

The Louisiana Soybean & Grain Research & Promotion Board supports research at the LSU AgCenter.

Bruce Schultz