Corn rootworm findings in Ontario an early alert for rotation choices

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Results of the 2023 Ontario corn rootworm (CRW) trap sites monitored through the Adult Corn Rootworm (CRW) Trap Monitoring Network have been released, tallying up the scope and scale of rootworm issues in the province and where farmers may need to make key decisions for 2024 based on risk level.

Ontario provincial entomologist Tracey Baute has summarized the initial findings on Field Crop News. There were 59 trap sites in 2023, which showed that CRW adult activity peaked in different weeks in August, depending on the region

Even though corn rootworm populations were 60 per cent lower than last year, 12 of the trap sites still reached or surpassed the CRW trap threshold of 2 beetles/trap/day. Baute says that these sites should be rotated out of corn in 2024 to knock back resistant populations and help to maintain what durability we have left in Bt-RW hybrids.

Counties most at risk of experiencing corn rootworm issues next year including unexpected injury in Bt-RW hybrids include: Chatham-Kent, Perth and Huron (High: 2 – 4.9 beetles/trap/day); Middlesex, Oxford and Waterloo (Very High: 5 – 9.9 beetles/trap/day); and Perth and Wellington (Extreme: >10 beetles/trap/day).

2023 CRW Trap Network-InfoGraphic (Supplied)

Continuous corn production that has relied heavily on repeated use of Bt-RW hybrids is risking losing valuable management tools to resistance, she adds.

Turning to hybrids containing RNAi traits in fields with Bt resistant populations will drive resistance to RNAi more quickly since it’s the only trait left to manage rootworm, Baute says, as it becomes essentially the only mode of action working. Rootworm has a history of adapting quickly when only one tool is repeatedly used against it.

Baute says that a more sustainable corn rootworm management practice is to rotate fields out of corn for one year after three years of continuous corn to knock back rootworm populations. This results in lower risk of rootworm the following one to two years, where other management tools can be used if needed. More information on sustainable rootworm management can be found on the Manage Resistance Now website.

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