ONTARIO GRAIN FARMER AGRONOMY 38 Dr. Jocelyn Smith has a favourite insect, and it’s one Ontario corn growers love to hate. As a research entomologist, Smith is drawn to the resilience of the corn rootworm. And her work to better understand it is helping farmers manage one of their most problematic pests. Last year’s growing season was an especially bad year for corn rootworm, for both the western and northern corn rootworm subspecies that are found in Ontario corn fields. Smith says this pest pressure isn’t subsiding. Between the pest’s hardiness, the high numbers of mature corn rootworm beetles found later in the 2025 growing season, and growing Bt corn rootworm resistance, this pest is becoming an increasingly serious issue. In a high-pressure year like last year, corn rootworm can result in up to a 50 per cent financial loss in fields with continuous corn. Jeanine Moyer Dealing with corn’s most persistent pest Keeping corn rootworm in check Livestock-dense counties, including Huron, Perth, Middlesex, and Oxford, are among those dealing with the heaviest corn rootworm infestation. And it’s not just the final yield loss that cuts into a grower’s bottom line. Corn rootworm can also create havoc at harvest, slowing down combines and adding extra labour hours if pest infestation is high enough to cause lodging. “Growers need to take a long-term approach to corn rootworm management, not just one year at a time,” says Smith, associate professor of field crop entomology at the University of Guelph Ridgetown Campus. “Bt resistance is on the rise, making it more important than ever that everyone, including those who grow corn for livestock feed, understand their risk and incorporate management tools.” ROTATE TO CONTROL A relatively easy solution to manage corn rootworm is to stop growing continuous corn in the same field. “I can’t stress enough that crop rotation and reducing continuous corn is the best management approach,” Smith says. Here’s why. Corn rootworm mostly lay its eggs in corn fields and its larvae can only grow on corn. So, the most effective and cost-efficient way to control it is to rotate to a non-host crop like soybeans or alfalfa. Volunteer corn can also support corn rootworm populations. Photo: Winston Beck, Iowa State University, Bugwood.org
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