Corn Rootworm: Living on the Fringe
Corn rootworm is not a new challenge for our region, but it has become increasingly problematic over the last three years. While traditionally viewed as an issue in southern areas with more corn in rotation, it spreads further north each year.
Identification of rootworm larvae can be difficult. Notice how small the worms are after hatching. These photos were taken in Pelican Rapids, MN on 6/19/24
In southern Minnesota, corn rootworm is a regular issue, but now it’s being seen much further north. Over the past three years, there has been a noticeable northward shift of about 75 miles.
In 2023, areas like Rothsay, Minn., and Hankinson, N.D., saw significant infestations. Collaboration with the University of Minnesota shows that most of these increased populations are mostly due to northern corn rootworm rather than western corn rootworm.
The northern beetles appear more tolerant of colder temperatures compared to the western beetles. Over the last few years, northern corn rootworm has emerged as the primary challenge, as it tends to travel farther and infest fields that may not have been planted with corn the previous year. This contrasts with western beetles, which are more localized to a single field.
Above is a poll of our expected traited needs for the 2026 season.
Notice the extreme variability depending on geography.
The University of Minnesota is also closely examining the role of extended diapause in northern corn rootworm populations. While extended diapause has been discussed for over 15 years, it hasn’t been a consistent concern until now. Open winters and lack of deep frost may be contributing factors. The 2025 season will be particularly revealing, especially in areas hit hardest in 2023.
I suspect the severe infestations in 2023 were largely due to drought conditions and early beetle emergence with a warm May. In contrast, the wet spring and summer of 2024 likely increased beetle mortality and allowed plants to outgrow damage, resulting in fewer issues than the prior year. As of the beginning of March 2025, the ground has been frozen since the new year and soil temperatures have finally dipped below freezing down to around 30” for most areas. The longer we can keep the ground frozen will only help kill more overwintering eggs unlike winter 2024 when the soil was only below 31 degrees at 8” for about 13 days.
What are we doing to combat rootworm?
Across central Minnesota and central South Dakota, many growers have significantly increased their use of SmartStax hybrids. In some areas, growers are now planting up to 80% SmartStax hybrids, compared to less than 5% just three years ago. Forecasting a traited product has become a challenge when thinking ahead 2 growing seasons for seed production.
Since we are in a fringe area for corn rootworm, we need to explore all available options. While I don’t see this as a long-term problem—especially if we have an old-fashioned harsh winter with temperatures dropping to -40°F—it’s critical to address the short-term challenges to protect crops. Planning ahead is the key to success.
Many growers on rotated acres chose not to use insecticides or traited products in 2024, leading to some issues, particularly with late-season standability. Steps must be taken in 2025 to prevent similar problems.
On acres with low rootworm pressure, an infurrow product containing bifenthrin, such as Capture, may suffice, though it isn’t foolproof. Under heavy pressure, these options won’t provide adequate protection.
The most reliable solution is still traited hybrids like SmartStax, which offer 100% confidence in controlling populations.
The above image shows extensive root damage from corn rootworm larvae, weakening the plant and increasing lodging risk. Management strategies like crop rotation, traited hybrids and insecticides help protect yield potential.
Key Management Strategies
1. Traited Products: For corn-on-corn acres, planting a traited hybrid like SmartStax is essential for effective population control. Pay close attention to fields with significant rootworm pressure in 2023, as these are likely candidates for extended diapause issues in 2025.
2. Adjacent Fields: Fields adjacent to problem areas in 2024 should also be considered for traited hybrids in 2025, as northern rootworm tends to travel farther.
3. Insecticides: On marginal acres, an in-furrow insecticide like bifenthrin can be helpful, though it’s not a foolproof solution. Under heavy pressure, bifenthrin may not provide adequate control, but it can still preserve up to 15 to 40
bushels of yield. Dry insecticides, while extremely effective, are generally avoided due to safety concerns and are only considered when pressure is extremely high.
4. Monitoring and Planning: Use sticky traps during the summer to monitor beetle populations and plan ahead. Spraying adult beetles during the season can reduce populations but is more of a temporary fix and not a sustainable solution.
5. Proactive Planning: The best defense is to plan ahead. Use winter downtime to create a comprehensive strategy for the upcoming season to mitigate problems effectively.
