Research Highlights

Finding the best solutions to manage insect pests in Virginia soybeans

By Carol Brown

For soybean growers in Virginia – or anywhere for that matter – scouting fields for insect pests is the best way to find issues.  Sally Taylor, assistant professor of entomology at Virginia Tech University, is a scouting proponent.

“The best way to know what is in your fields is to scout,” Taylor said. “Knowing what pests are there, or not there, could save money on input costs and help farmers make the right management decisions.”

Taylor is conducting research at two locations in Virginia on best management practices for handling insect pests in soybeans. The research project is supported by the Virginia Soybean Board.

The project includes integrated pest management (IPM) studies in both full-season and double-cropped soybean systems in Maturity Groups (MG) 4 and 5. She is comparing no insecticide treatment with a standard tank mix and three different IPM approaches for stink bugs, corn earworm and soybean looper.

Using an IPM approach means responding to pest issues in the most effective way with the least amount of risk to profitability or the environment.

The research includes different treatments as not one insecticide kills all pests. If there would ever be a blanket insecticide, it would kill the beneficial insects as well.

“There is a bit of an overlap in time between caterpillar pests and stink bug pests,” Taylor said. “Now through mid-August is the earworm flight. We’ll start to see stink bugs usually in August. As we get toward September there will be a wave of foliage-feeding caterpillars including soybean looper.”

Taylor wants to show farmers they don’t need to spend money unnecessarily on pest management. They would see a big cost savings if they stop putting pest management inputs into the system that aren’t needed, she said, but also recognizes that producers could add an insecticide with a fungicide to take care of two issues at once.

Research results showed the MG4 soybean tank mix treatment site was the only area that had stink bug counts higher than the allowed threshold (five bugs per 15 swipes) when the site was checked on Aug. 21. The insecticide tank mix was applied on July 26 at the R3-4 growth stage. Taylor reported that after three weeks, there was little to no residual product for stink bugs. She cautioned that spraying before infestations begin could eliminate beneficial predators and worsen problems.

Non-chemical solutions

There are alternative ways beyond chemical applications to help reduce insect problems in soybeans and Taylor is looking into these as well.

“There are ways to deter pests through non-chemical strategies such as increased planting densities and narrow row spacing, where canopy closure is completed before the major earworm flight and largely avoided,” she said.

But with double-cropped soybeans, this becomes more difficult, she warned. It’s all about timing — it must work correctly to harvest the wheat crop and plant soybeans to reach canopy before the moths arrive.

Managing for maturity helps with the late-season pests, Taylor said. If farmers get the crop in the field and out of the field earlier, they won’t need to worry as much about pests in September.

Scouting aids

Farmers can use a beat cloth to help with scouting for insects, which Taylor has been giving out at field days and winter workshops.

A beat cloth is a length of material with poles attached at both ends. It is easily spread on the ground underneath the soybean plant. Taylor says to shake two soybean plants into each other above the cloth and the insects will fall onto the cloth. It’s an easy way to visualize and count the insects.

“We’ve held scouting clinics in the past in several regions of Virginia,” Taylor said. “At the meetings, farmers get disease and pest scouting lessons. They receive a free beat cloth along with a set of laminated cards that help identify bugs, provide product application rates and more. They’ve been well-received.”

After the first full year of results and this year’s research well in-hand, Taylor says that insect pressure can depend on many variables: location, planting date, maturity group and previous applications. But the best way to manage pests is to scout before making management decisions for the field.

Photos courtesy Sally Taylor

Published: Sep 9, 2020