Mild winter means increase in soybean pests

LSU AgCenter entomologists and graduate students are conducting two research projects to determine ways to improve the economics of soybean farming.

Jeff Davis, AgCenter entomology professor, is looking at insecticides that do a good job of controlling redbanded stink bugs as well as insecticide resistance.

“We are monitoring soybeans to stay on top of what’s happening in the fields, and we are prepared to get out there and determine problems so we can advise growers on what they should do,” he said.

The current work on pests in soybeans should cause a decrease in the amount of money growers must pay for pest control.

“After the mild weather we had this winter, we are expecting the numbers of redbanded stink bugs to be higher and earlier,” he said.

Davis and his student are collecting stink bugs from every parish to determine their tolerance to insecticides.

“We are focusing on three products that are being used to control the stink bugs — neonicotinoids, pyrethroids and organophosphates,” he said. “We know that most of these products work well against stink bugs, but some cause increased feeding.”

When looking at the economics of the products, the question becomes, “do we kill the insects or protect our soybean yields?” he said.

Weather has been a major factor for growers over the past few years, which allows stink bugs to feed on the beans and cause injury and yield decrease.

“If we could control the weather, that would be the ideal way to control stink bugs. But the next best way is through host-plant resistance,” he said. “This means having plants that are able to protect themselves against pests.”

The project is in the third and final year, with results coming soon, as Davis’ student will soon be graduating.

Davis’ second research project is the control of soybean loopers, which is closely connected to stink bug control.

“Sometimes when we find an effective control for stink bugs it causes the loopers to flare, and their feeding increases,” Davis said.

What is happening in fields across the South is soybean loopers are now showing resistance to the chemicals that had been effective.

“We have been documenting over the past few years the resistance to insecticides by soybean loopers,” Davis said.

He said his colleagues from across the South are sending him soybean loopers, and he is testing them for resistance.

The loopers are not a problem during the early part of the growing season but are known to start showing up in high numbers in July.

Growers need to find better timing schedules for sprays, he said. The problem is when the numbers are at their highest is the same time that the beneficial insects are also in the field.

“So there is the problem of killing pollinators while trying to decrease the redbanded stink bug population,” he said.

During the period when the soybeans are in the R2 and R5 stages, the female ratio is much higher than the males.

“Our question is, can we time our sprays to target the females?” Davis said. “The problem is at R2 there are more beneficial insects in the fields.”

Davis said at this time of the year the female redbanded stink bugs outnumber the males nearly two to one. However, anything that kills the redbanded stink bugs will also kill a lot of the other insects, he said.

Another approach is to use parasitoids to help in the control of soybean pests.

This story is featured in the Louisiana Soybean and Grain Research and Promotion Board 2020 Report.

Soybean IPM Looper Tachnid Flyjpg

The tachnid flyis a parasitoid used to help in the control of soybean pests. Photo by Ilgoo Kang
9/16/2020 4:24:36 PM
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