Description
Corn rootworm continues to adapt to the tools used to control it, and Ontario and Quebec have become leading hot spots for resistance in North America.
In this episode of RealAgriculture's Corn School, Ontario Ministry of Agriculture, Food and Agribusiness entomologist Tracey Baute explains why resistance is increasing in continuous corn production systems and what growers can do to protect the effectiveness of both existing Bt traits and newer technologies, including RNAi.
According to Baute, Ontario and Quebec recorded the highest corn rootworm populations in North America in 2025, particularly in regions where corn is grown year after year.
"We're continuing to see these hotbeds where there is repeated corn-on-corn," says Baute, pointing to areas of Huron, Perth, Middlesex, and Oxford counties where populations continue to flourish despite Bt corn.
The reason is straightforward: corn rootworm is highly adaptable, and repeated use of the same management strategy creates selection pressure for resistant populations. Baute says many growers have relied heavily on Bt corn to manage the pest, but emphasizes that "the best management tool for corn rootworm is rotation."
Growers following a three-year crop rotation generally aren't experiencing the same level of resistance. In contrast, continuous corn production allows surviving rootworm populations to multiply and spread, making additional control measures less effective over time.
For 2026, Baute expects another high-risk year for corn rootworm and encourages growers to monitor fields with traps to better understand their risk.
She also stresses the importance of alternating management strategies rather than relying on a single tool. Crop rotation remains the foundation of an effective management program and will also help preserve the lifespan of newer technologies, including RNAi, as they become available.
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