Entomology graduate assistant Chancy Sibakwe sweeps a soybean plot searching for insects at the LSU AgCenter Botanic Gardens at Burden. Photo by Avery Williams

When it comes to managing insects, soybean producers have to control an insect complex. It’s not just one main insect. It’s stink bugs, three-cornered alfalfa hoppers, corn earworms and other caterpillars.

So, LSU AgCenter entomologists are taking a multipronged approach to integrated pest management in soybeans starting with understanding insecticide resistance, which remains one of the greatest challenges for growers.

LSU AgCenter entomologist Jeff Davis’ research shows that redbanded stink bugs exhibit behavioral resistance by avoiding insecticide exposure.

“This insect feeds in the lower canopy. It lays its eggs lower in the canopy,” Davis said. “It avoids the insecticides because when we spray in a field, the insecticide reaches about the top third, and it pretty much lives in the bottom two-thirds.”

These insects also seem to have metabolic resistance. They can break down insecticides faster than our native stink bugs. He is also trying to understand if the redbanded stink bug’s exoskeleton protects it more from insecticides.

“We don’t know if it has a tougher exoskeleton or more waxes that protect it. So that’s some research we’re doing, trying to understand the actual mechanisms around that,” he said.

Davis and entomologist James Villegas are looking at new insecticide options and insecticidal seed treatments.

Villegas is evaluating the efficacy of insecticidal control strategies, including different application rates, combinations and timing, targeting key insect pests, specifically redbanded stink bugs, soybean loopers, corn earworms and fall armyworms.

Redbanded stink bugs continue to be the major pests of soybeans in Louisiana. Villegas said the state has the highest incidence of redbanded stink bugs in the Midsouth. He is evaluating a new insecticide, Vertento (isocycloseram), to help manage this and other pests. He said it seems promising and can last longer in the field.

“It has a lot longer residual than other products that we have in the market,” Villegas said. “If you time it right later in the season, you can eliminate a spray before harvest.”

Costs can be prohibitive with some of the new insecticides. Villegas’ research focuses on the importance of aligning management decisions such as seed treatments and insecticide applications with historical pest pressure in specific fields so farmers can make the most economically sound decisions.

The researchers are also looking for products that won’t harm pollinators but are active against stink bugs. They are testing experimental compounds and combinations of available insecticides to extend control.

With insecticides, there is also the question of how best to apply them. Villegas is researching the use of sprayer drones for insecticide applications on soybeans. He is working with LSU AgCenter engineer Randy Price. They established field plots at the Dean Lee Research and Extension Center, and trials have shown drones can be as effective as traditional application methods such as sprayer rigs and planes.

“There is an increasing number of producers that also use sprayer drones in their field,” Villegas said. “The idea for this is for us to really look at what would be the best way to put out the products to control your target insects in soybean.”

The researcher is looking at optimal flight heights, nozzle types, spray rates (GPA), and insecticide classes. He has found flying between 10 to 15 feet above the canopy and higher GPA is where you see a lot better control.

“Our goal is to continue building baseline data on drone-based application strategies and their effectiveness in managing insect pests.”

Another project is looking at how production practices can affect pest pressure. Davis is researching how the use of paraquat as a harvest aid may influence insect damage. He found that as the soybean plants dry down, pods may become more appealing to insects.

“You’re breaking down that physical barrier, and the plant is no longer actively defending itself,” Davis said, adding that it could increase sugars in the plant. “If paraquat mobilizes sugars, we could actually be making those soybeans more attractive to insects.”

Davis is also investigating the unintended consequences of insecticide use at the system level. His research suggests that some insecticides used to control caterpillar pests may actually stimulate stink bug populations, increasing reproduction and survival under certain conditions.

The phenomenon known as hormesis may show that when an insect is exposed to a stressful situation, such as a low nonlethal dose of an insecticide, the insect may actually produce more progeny.

“Think of it as that which doesn’t kill us, only makes us stronger,” Davis said.

Davis noted that he is always thinking broadly in a whole-system-levels approach to integrated pest management to get the best results for soybean growers.

A sprayer drone flies over a soybean field at the LSU AgCenter Dean Lee Research and Extension Center. AgCenter researchers are investigating the use of sprayer drones for insecticide applications on soybeans. Photos by James Villegas

LSU AgCenter entomologists are taking a multipronged approach to manage soybean pests such as the redbanded stink bug.