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Research Highlights

Research Highlights
Exploring and Combating Pests in Kentucky Soybeans

Ground beetle preying an immature slug. Photo: Josey Tolley

By Carol Brown

At the University of Kentucky Research and Education Center at Princeton, Assistant Professor Raul Villanueva has a full schedule. The only entomologist at this Extension site, he helps farmers identify and combat insects and other pests invading crops, focusing on his work on soybeans, corn, and wheat. 

He has been conducting several research projects to assess the pests that impact soybean plants in the state. 

“With projects supported by the Kentucky Soybean Promotion Board, I’ve been looking at slugs, the brown marmorated stink bug, the bean leaf beetle, and the Dectes stem borer,” Villanueva says. “Some are common pests in Kentucky, and some are relatively new, such as slugs, and increasing in soybeans every year.”

Each of Villanueva’s research projects has a different emphasis but also similar goals. For instance, he is measuring pest populations in all projects, which can help determine their invasiveness, impact, and movement within the state. Additionally, he is conducting research on the efficacy of different insecticides on the bean leaf beetle, the brown marmorated stink bug, and other pests. Another project is looking into improving soybean resistance to the Dectes stem borer.

Figure 1. Species composition of stink bugs that feed on soybeans in several counties in Western and Central Kentucky between 2020 and 2021.

“In general, the stink bug is probably the most important pest of soybeans across the U.S., as they feed on the soybean pods. We have seen the expansion of the brown marmorated stink bug in western Kentucky soybean fields,” Villanueva says. “This insect has been present in eastern Kentucky since 2010, but for unknown reasons they hadn’t moved to the large areas of soybean acres in the western part of the state.”

But by 2021, the species composition changed greatly, he says, with the brown marmorated stink bug populations rising to 40.6 percent of recorded stink bugs in western and central Kentucky counties. When compared to the previous year, among the different species counted, only 14.6 percent were brown marmorated stink bugs (Figure 1).

“Last year we focused on population expansion of the brown marmorated stink bug,” Villanueva comments. “This year we are going to pinpoint the efficacy of certain pesticides on this particular pest. We will be isolating plants in the fields using nets and comparing them to soybean plants without protection. We will be looking at soybean seed quality, the effectiveness of different pesticides and more.” 

Figure 2. Soybean median (line in box) yields on 40 cultivars grouped in 5 categories depending on Dectes percentage infestation. Numbers below each category indicates the number of cultivars (CVS) per group. (Whiskers show the upper and lower range, box shows the upper and lower quartile.)

With the Dectes stem borer project, Villanueva and his research team compared soybean varieties, also known as cultivars, that should be more resistant to lodging with cultivars that may lodge easier. The Dectes stem borer larvae tunnels and eats its way through the pith in the soybean stem, causing the stems to weaken. Weakened soybean plants can more easily become lodged or bent, particularly after high winds or rains, which causes yield losses and harvest difficulties. Results from this project showed that of the 40 commercial cultivars planted, 13 did not have any damage by Dectes, and 27 cultivars had between 5 to 33 percent of the plant infested. However, yields were not affected by the infestation patterns (Figure 2).

The bean leaf beetle research project entailed studying the efficacy of single and double modes-of-action insecticides. Villanuevae and his research team tested Leverage® or Hero® (double mode-of-action) and Baytrhoid XL, Warrior II with Zeon technology, and MustangMaxx (pyrethroids) on replicated research plots at Princeton. They also conducted laboratory tests with MustangMaxx, Hero, and Lorsban, which caused 90 percent or higher population mortalities. Whereas Warrior, MustangMaxx, Hero, Leverage, and Lorsban completely deter bean leaf beetles from feeding on soybean leaves for 48 hours.

Left: Dectes larva in soybean stem. Center: Dectes adult feeding on foliage. Right: Plug of fiber that seals overwinter next near base of the plant.

For the 2022 season, Villanueva will continue working with the stink bug pest and slugs. Slugs were a sporadic pest in the past, he says, but are now a more frequent pest affecting soybean seedlings and have forced farmers to replant in recent years in many states. He will evaluate molluscicides (pesticides that kill mollusks, like slugs) and ground beetles, which are slug predators.

There are numerous pests wanting to lunch on the soybean plant in Kentucky and across the country. By conducting the research to find out which pests are present and what works to reduce their damage, researchers including Raul Villanueva are valuable assets to the farmer and to the soybean industry.

Other checkoff research projects:

Evaluating the presence of the Dectes stem borer in soybean

Assessing the management of bean leaf beetles and pod mottle virus infections in soybeans

This project was funded by the soybean checkoff. To find research related to this research highlight or to see other checkoff research projects, please visit the National Soybean Checkoff Research Database.