The “billion-dollar bug” is sharpening its teeth for 2026. Bayer CropScience reports corn rootworm pressure could be significant this year across major corn growing areas.
Based on 2025 beetle capture data from 555 monitored fields, the company projects medium to high rootworm pressure for the upcoming growing season in much of the Midwest:
- 31% of the corn fields sampled in 2025 had counts exceeding the economic threshold of 2 beetles/trap/day, which was 2% higher than 2024 fields (29%), 22% less than 2023 and 2022 fields (53%), and 7% less than 2021 fields (38%).
- 46% of the continuous corn fields sampled in 2025 were above the economic threshold, which was up 3% from 2024 (43%), down 25% from 2023 (71%), down 28% from 2022 (74%), and down 6% from 2021 (52%).
- 17% of the first-year corn fields in 2025 were above the economic threshold, which was 1% higher than 2024 (16%), 3% higher than 2023 (14%), up 7% from 2022 (10%), and equal to 2021 (17%).
On a broad scale, Bayer reports that rootworm larval populations — and consequently the risk potential from all CRW species this season — are likely to be elevated in fields in northern Illinois, south central Illinois, western Iowa, eastern, southeastern, and southwestern Nebraska, eastern and southeastern Wisconsin, and northern Colorado. Read the full report here.
Rootworm larvae feeding on corn roots compromise the plants’ structural integrity and can slice yields in affected fields by as much as 45%.
How Two CRW Variants Beat The Corn-Soybean Rotation
“CRW beetles are very, very adaptable to many of the things that we throw at them,” says Ashley Dean, Iowa State University Extension field crop entomologist.
She says CRW is forcing many row-crop growers to rewrite their management playbooks to address the pest better, especially variant populations.
Dean reports that the “variant” label describes two distinct genetic adaptations of corn rootworm:
- Northern Corn Rootworm (Extended Diapause): These small green beetles have learned to hit the “snooze” button. Instead of hatching the following spring, their eggs remain dormant in the soil for two or more years—sometimes up to five. This allows larvae to emerge exactly when a field rotates back to corn.
- Western Corn Rootworm (The Soybean Variant): These yellow-and-black striped beetles have developed a behavioral shift. Instead of staying in cornfields to lay eggs, females migrate to soybean fields to deposit them. When that field is planted to corn the next season, the larvae are already waiting in the soil. “These variants have essentially lost their fidelity to corn when they’re laying eggs,” Dean notes in a webinar.
A Multi-Pronged Management Strategy
Addressing corn rootworm effectively requires farmers use a localized, field-by-field strategy, says Jim Robinson, chief technology officer for Rob-See-Co. Because geography, soil, and history vary, growers should work with agronomists to tailor traits and stewardship practices to their specific acres rather than relying solely on regional forecasts, he advises.
Here are four additional recommendations Extension and industry advise farmers use in areas with expected high populations of CRW this season:
- Make Root Scouting Non-Negotiable: Dig and rate roots in every field—continuous or rotated—to understand your baseline pressure. For assessing damage, use the interactive node-injury scale from Iowa State available here.
- Consider Longer Rotations: In areas with heavy Northern corn rootworm extended diapause, adding a third crop like oats can break the cycle, Dean says.
- Strategic Use of Bt and Insecticides: While Western corn rootworm has shown resistance to all four Bt traits in some areas, these tools still have a place. However, Iowa State suggests choosing either a Bt hybrid or a soil-applied insecticide rather than using both as “insurance” unless pressure is extreme.
To help farmers make informed decisions, Chris DiFonzo, professor & field crops entomologist at Michigan State University, provides the Handy Bt Trait Table for U.S. Corn Production, a valuable resource that outlines available Bt traits, their targets, and other key information.
- Leave a Check Strip: When testing a new transgenic hybrid or insecticide in first-year corn, leave an untreated strip. This is the only way to verify if the treatment provided a return on investment.
