Rotation, rotation and more rotation.
That’s the top priority many experts will give corn growers grappling with corn rootworm or European corn borer, although new tools are coming to replenish farmers’ depleted toolbox against the issue.
WHY IT MATTERS: Farmers have long been told to take steps to protect the efficacy of Bt genetics, such as ensuring that a variety has multiple Bt traits.
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Corn rootworm and European corn borer are problems.
In recent years, the latter has been a problem held back less and less by the Bt genetic traits that Canadian farmers have come to rely on, Manitobans included.
Nova Scotia was the first province in Canada to realize there was an issue, after varieties with protection based on the Cry1F protein started to slip in their control. By 2020, Cry1F resistance had also been detected in Quebec and Manitoba.
Western corn rootworm was found in Manitoba for the first time in 2021, although northern corn rootworm has been hanging around since 2015.
Expert response to the challenge of corn-burrowing insects has ranged from on-the-ground farm practice changes — like longer rotation or shredding stalks, both of which interrupt the lifecycle of the pests — to newer solutions developed in the genetics lab.
Bayer, for example, is hanging hopes on RNAi, or RNA interference — a process in which RNA is used to control or silence gene expression. In this case, targeting a specific gene of rootworm larvae after they get munching, killing the pest.
Hybrids developed through that technology were on display during Canada’s Outdoor Farm Show 2025 near Woodstock, Ont., earlier this month.
Tools new and old
Producers are already warned to rotate their mode of action, not just their crops. That should include below-ground protection, if their production system and conditions warrant it, said Bayer researcher Annemarie Van Wely.
That’s one of the promises made by the company’s new VT4Pro trait, built into two released varieties this year. The company’s website cites three above-ground (Cry1A.105, Cry2Ab2 and Vip3Aa20) and two below-ground (Cry3Bb1 and the RNAi-based DvSnf7 dsRNA) anti-insect modes of action that come with the trait, along with Roundup Ready 2 herbicide tolerance.
Along with European corn borer and corn rootworm, the company says the trait is effective against fall armyworm, black and western bean cutworms, and corn earworm. It will be “a versatile product with a broad geographic fit, helping to provide farmers the protection they need,” according to a fact sheet published by Bayer Crop Science Canada.
Another note on the website, outlining the trait’s below-ground protection, says it will “help farmers with low-to-moderate corn rootworm pressure defend their roots.”
“You’re getting all that above-ground control, as well as the below-ground control,” said Phil Nadalin, a Guelph-based agronomist and customer solutions lead with Bayer.
The two hybrids are DCK094-94 and DC100-01.
The former has been a “real rock star” over the past couple years of testing under Ontario conditions when it comes to yield, Nadalin said.
The latter hybrid hits the 100-day window and similarly seems to be an adaptable crop with solid yield, he said.
