Corn earworm survived three correctly timed pyrethroid sprays in Wisconsin fields last summer, and 87% of fields sampled afterwards carried a resistance gene from the Old World bollworm. University of Wisconsin-Madison entomologist Emily Bick delivered the finding as a warning to corn growers who assume last year's spray program will hold up again.

"I got a report from a stakeholder that some of the fields that this particular crop consultant was monitoring had been sprayed correctly with pyrethroids — three sprays over the three weeks of silking, completely adequately — and yet there seemed to be a lot of corn earworm on the crop," Bick said. "We collected some of those insects, and across these three fields, 87% of those fields had that Old World bollworm gene, which is a problem."

Why is corn earworm resistance so variable?

Southern U.S. states have reported pyrethroid resistance in corn earworm for more than 10 years, driven by repeated exposure and by the resistant gene CYP337B3 transferred from the Old World bollworm (Helicoverpa armigera). That European species arrived in the U.S. around 2014 and interbred with local corn earworm populations, producing insects with a genetic makeup that tolerates insecticides better.

Because corn earworm migrates north each season and does not overwinter in Wisconsin, resistance levels shift depending on where the source populations originate. Bick cautioned growers against assuming last year's control program will perform the same way this season. Insects carrying the resistant gene may not even show up in 2026, meaning farmers could escape the pyrethroid failures seen a year ago.

The pest itself is recognizable in the field. Larvae run 1.5 to 2 inches long, colored green, pink or brown with dark stripes and a rough, microspined texture. The adult moth is tannish brown with a 1.5-inch wingspan and often a dark spot on each olive-gray forewing.

Treatment thresholds are concrete: act when traps catch five to 10 moths and 10% of the corn crop is silking. After spraying, Bick said, growers should assess control levels and confirm the strategy is working rather than assume it.

How close is soybean gall midge?

Soybean gall midge has devastated crops in Nebraska, Iowa and South Dakota and is moving steadily north. First detected in Minnesota in 2018, it spread across that state and, in 2025, was reported in Dakota County, Minnesota — directly across the river from Wisconsin.

"Last year, in 2025, soybean gall midge was reported in Dakota County, right across the river from us, which means that it may or may not, but likely will be, in our fields," Bick said.

No case has been confirmed in Wisconsin. "There hasn't been a single instance of it yet in Wisconsin," she said. "Once it's here, it's going to be a big deal. I just want farmers to be aware of its movement and what to look for in fields."

The midge attacks along field borders, laying eggs in stem cracks and fissures that form around the V2 growth stage. Plants are not susceptible before V2; after that point they become vulnerable. Scouting is difficult because the pest resembles other insects. Bick's diagnostic method: walk the field edge, take a small paring knife and peel back the skin of the soybean stem. Larvae are tiny and either bright orange or white depending on stage.

The work is labor-intensive, but Bick said it remains the only way to confirm a problem. This year she is bringing in experts from neighboring states to help scout.

"Since it's now across the border from us, maybe these experts can actually help us locate this pest in our state, which would then allow us to give better information to you all," she said. Researchers are already developing biological control options and management strategies for the pest.

What tools can growers use right now?

Three resources are available to Wisconsin growers:

• Insect Pest Text Alerts. Each week, University of Wisconsin Extension and the state Department of Agriculture, Trade and Consumer Protection (DATCP) report statewide insect findings to Bick's team, which sends text alerts with links to short articles covering identification, scouting, thresholds and control options. "That early warning heads-up is where it really, really helps," Bick said.
• Crop Pest Trap Networks. DATCP has trapped pests for more than 30 years. Its 2026 interactive maps show locations and counts for black cutworm, true armyworm, western bean cutworm, corn earworm and fall armyworm, plus black light traps monitoring moth flights.
• UW Extension Pest Management page. Longer-form news, tools, training and educational guides for managing individual pests. "We've spent a considerable amount of time putting these resources together," Bick added. "We're hoping you use them."

Growers should watch trap counts through silking, scout field borders for stem damage after V2, and expect Bick's cross-state scouting effort to confirm whether soybean gall midge has crossed into Wisconsin this season.