From Agronomist Brandon Hulme
Corn rootworm resistance to Bt corn is becoming a bigger issue in the U.S. Corn Belt. Increasingly more acres have been planted with Bt hybrids, which are designed to produce insect-killing proteins from Bacillus thuringiensis (Bt). But rootworms, especially western corn rootworms, have adapted. Over time, some populations have developed resistance to certain Bt traits, which means the technology isn’t working as well as it used to. And that means yield losses are more likely.
No tool stays effective forever on its own. But, understanding how resistance develops and using a mix of management strategies will help keep Bt working longer and protecting your bottom line.
How did corn rootworms become resistant to Bt corn?
When corn rootworms are repeatedly exposed to the same Bt trait year after year (especially in corn-on-corn fields), any rootworms that happen to carry resistance genes are more likely to survive and reproduce. Over time, more of the population becomes resistant because the susceptible ones are killed off. The survivors pass on their resistant traits and their offspring gradually dominate.
As rootworms become resistant, the Bt toxins become less effective at controlling them, leading to increased root damage, lodging and, ultimately, yield reductions.
According to Penn State Extension, multiple locations across the Corn Belt have seen resistance to Bt traits evolve independently. This suggests that the resistance genes were already present in rootworm populations and activated under strong selection pressure. And to compound the problem, some populations have also developed cross-resistance. This means they are resistant to multiple Bt toxins, even if they weren’t previously exposed to them.
Which management strategies can help me combat Bt-resistant rootworms?
Adopting sustainable management practices is vital to preserve the effectiveness of Bt technology and ensure the long-term viability of corn production in the Corn Belt. At Champion Seed, we recommend a mix of management strategies to help protect your fields. Here are four tips to consider:
- Crop rotation remains one of the most effective ways to keep rootworm numbers in check. Rotating corn with a non-host crop, like soybeans, breaks up the pest’s lifecycle and helps reduce the selection pressure that drives Bt resistance.
- Planting hybrids with multiple Bt traits (pyramids) can help delay resistance, but it’s not a silver bullet. As cross-resistance becomes more common, this strategy is losing some of its punch. But that means it’s even more important to rotate modes of action and integrate other control tools.
- Regular scouting matters. Keeping an eye out for adult rootworm activity and checking roots for feeding damage gives you an early read on resistance issues. This will help you make more informed decisions for next season.
- No single tactic is enough on its own. A solid Integrated Pest Management (IPM) plan brings it all together — rotation, trait selection, refuges and regular scouting — to keep rootworm pressure in check and your fields productive for the long haul.
Can you help if I’m seeing rootworm damage?
If you are seeing rootworm damage and down or lodged corn, contact your local Champion Seed dealer and they can help you through this process. If you aren’t sure which kind of corn rootworm pressure you have in your area, we have rootworm traps that can help you get an accurate count of the pressure in your fields. For the most accurate count, it’s best to place these traps at tassel.
And when it comes to planning for next year, look at these traits for your best defense against corn rootworms:
- SmartStax® Pro is our strongest trait against corn rootworm. We recommend it for areas with known issues and long-term corn-on-corn acres. It offers three modes of action against rootworm, including the ability to disrupt essential gene functions. This leads to pest mortality. Even better, this mode of action does not rely on Bt traits — which means it is effective against Bt-resistant corn rootworm. For optimal control of rootworms, we recommend using SmartStax PRO with IPM strategies.
- The 2026 Champion lineup includes six NEW SmartStax Pro hybrids, for a total of 11 hybrids with the highest level of rootworm protection.
- SmartStax® has two modes of action against rootworm. It has been on the market since 2009, so some insects are showing resistance to this protein. It’s good for first-year corn-on-corn fields and potentially for the second year.
- Duracade® has two modes of action against rootworm and is newer to the market. It does have some known insect resistance but is a solid trait for bean ground and first-year corn-on-corn fields.
Learn more about SmartStax and Duracade in managing corn rootworm.
Champion Bio Max Corn can also add a level of protection. It contains GUARD X™ bioinsecticide that helps mitigate corn rootworm damage by repelling these pests rather than killing them. Plus, you get the added benefits of early emergence and plant vigor and drought and water stress reduction throughout the season.
