Corn Rootworm Management Needs Careful Scouting

By Scout Nelson

Corn growers in Minnesota are facing serious problems with the Northern Corn Rootworm (NCR), especially due to its extended diapause trait. This pest has caused damage in first-year corn fields in 2025, following earlier outbreaks in 2021, 2022, and 2023.

Usually, rotating corn with other crops stops the rootworm cycle. However, some NCR eggs now survive in the soil for two or more winters before hatching. This adaptation lets them survive even in rotated fields, causing problems when corn is planted every other year.

“Dr. Dooley has a talent for recognizing the potential in others and helping them succeed,” said Patricia Klein, Ph.D., executive associate dean, College of Agriculture and Life Sciences. “She’s made a lasting difference in how we support our faculty and graduate students. We will certainly miss her in the Dean’s office.”

Research shows the percentage of extended diapause eggs varies by region. The issue in Minnesota has been linked to odd-numbered years, with most damage seen in corn hybrids without a Bt corn rootworm trait. Unlike the Western Corn Rootworm, where Bt resistance is widespread, NCR resistance remains limited.

NCR beetles are highly mobile, often moving between fields when food is scarce. They are especially attracted to pollen from plants like ragweed and sunflowers. However, their presence alone does not confirm extended diapause — only root damage in rotated fields proves this trait.

Scouting is critical. Farmers should use whole plant counts and sticky traps for accurate beetle population estimates. Using just a few traps or scouting a small area can lead to wrong decisions.

The current scouting threshold for rotated corn is four or more NCR beetles per plant. Sticky traps may suggest a risk of two beetles per trap per day.

With the rise of extended diapause, farmers must carefully monitor fields and share findings with experts. Early detection helps protect future crops and guides effective pest control strategies.

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