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Corn rootworm pressure high in Ontario

August 24, 2020  By Top Crop Manager

The 2020 growing season has seen increased pressure from corn rootworm (CRW), a significant corn pest in Canada. So much so, the Canadian Corn Pest Coalition has issued a warning about potential resistance development to Bt corn rootworm hybrids.

According to a recent post on Ontario Ministry of Agriculture, Food and Rural Affairs’ (OMAFRA) Field Crop News, high CRW pressure in Ontario in 2020 is challenging current Bt corn rootworm hybrids and several growers of Bt rootworm hybrids are reporting unexpected injury by CRW to trait providers and research and extension scientists.

Corn rootworm resistance to Bt traits is widespread in the U.S. and resistance may be a factor contributing to unexpected injury on Bt corn rootworm hybrids in Canada. While most of the injury by CRW larvae has already occurred by August, growers should still scout their fields as soon as possible to determine whether root injury, lodging, goose-necking or high levels of adult CRW beetles are present. Scouting will help determine if these fields need to be managed differently next year to reduce the risk or spread of resistant populations.


Tracey Baute, OMAFRA field crop entomologist and creator of the Baute Bug Blog, has compiled a list of tips and best practices for scouting corn rootworm. Above all, she highly recommends scouting fields before early September, while rootworm adults are still active.

For farmers who depend on silage corn for livestock feed, Christine O’Reilly, OMAFRA forage and grazing specialist, has created a resource detailing alternative forage crop options. According to O’Reilly, the best management practice to reduce resistant CRW populations is to rotate out of corn for at least one year. Corn rootworm beetles typically lay their eggs in corn fields. If that field is rotated to a non-host crop the following year, the larvae will die after hatching and the population will be eliminated.

Growers are encouraged to use alternative forage options to replace silage corn for a minimum of one year, but ideally for the next two to three years, O’Reilly writes.


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