The Minnesota Soybean Research & Promotion Council is leading the charge and investing checkoff dollars to proactively ensure that “the dreaded unknown” has less of a devastating impact on Minnesota soybean growers. You know. The one that typically comes back to haunt you.

The soybean tentiform leafminer is one of the unknowns that MSR&PC is investigating through an agronomic research project with the objective of building the foundation for the development of management programs for the insect. 

“We don’t know how serious the situation is,” MSR&PC Director of Research David Kee said. “We need to find out exactly how big of a problem the soybean tentiform leafminer is and determine what our options for control are.” 

First discovered attacking soybeans in the U.S. in 2021, the soybean tentiform leafminer is a tiny moth native to North America and is known to feed on American hog peanut and slickseed fuzzybean. Now that the insect has broadened its palate to include soybeans, yield damage is a very real concern. 

“Since its emergence into soybeans, we’ve seen it every year and we’re finding it across a broader geography,” said University of Minnesota Professor and Extension Entomologist Robert Koch, who is the principal investigator on the project. “I’m not sure yet if it’s spreading across the soybean growing region or if we’re just getting better at finding it where it already occurs.” 

Either way, Minnesota soybean growers need to be on the lookout. In 2023, soybean tentiform leafminer was found in 77 fields across 44 counties in Minnesota and North Dakota.  

“It’s a tiny little moth that lays its eggs on the leaves of the soybean plant,” Koch said. “Then, the larvae hatch and enter the leaf, spending their lives feeding on the tissues inside the leaves, creating a tunnel and hollowing out the leaf, which inhibits photosynthesis. And, if you get enough of that happening, we’re concerned that it could cause yield loss.” 

Koch’s research has two primary goals: evaluate the efficacy of insecticides against soybean tentiform leafminer in soybean fields and assess the diversity and impacts of parasitic wasps attacking soybean tentiform leafminer populations. During the first year of the project, Koch tested the efficacy of Agri-Mek and Endigo ZCX, which have translaminar properties. This growing season, Koch is continuing his research and including additional commercially available insecticides to begin building a foundation for Minnesota soybean growers to reference. 

“We’re focusing on insecticides that have a special kind of property called translaminar activity,” Koch said. “A lot of insecticides kill what’s on the surface but with translaminar insecticides the molecules can move through the tissue of the plant, which we’re suspecting we need for this pest. So, we’re focused on a couple of different insecticides that have that property.” 

Though more testing is required before a strong recommendation can be formed, Koch has discovered important information for growers. 

“We were able to get good control when the caterpillars were very young but once they got older the insecticides weren’t very effective,” Koch said. 

As part of the research project, Koch is also investigating biological control methods to combat soybean tentiform leafminer infestation.  

“We wanted to see if there were any parasitoids associated with the soybean tentiform leafminer,” Koch said. “So, last year we started doing some sampling to see what was there and we found more than 15 different species of tiny parasitic wasps that are attacking the leafminer. With MSR&PC’s support we’re continuing that research.” 

Between elemental weather, invasive weeds, problematic diseases and damaging insects, Minnesota soybean growers must remain vigilant. With the help of MSR&PC and wise soybean checkoff investments, growers have access to the research they need to maintain an effective pest management program. Koch’s soybean tentiform leafminer research is a prime example of checkoff funded research that’s focused on future problems producers may face, aiming to have answers ready before the questions begin. 

“We found a problem and now we’re employing checkoff dollars to determine how big the problem is and what our options for control are,” Kee said. “It’s an excellent use of checkoff money.”