Corn Rootworm Outlook

Corn rootworms are the Goldilocks of the insect world -- they don’t like it too dry, they don’t like it too wet. But, they’re also very unpredictable, making it tough to get the upper hand on these destructive pests.

Jim Lappin is the crop marketing manager with AMVAC Chemical Corporation. He says beetles tend to be concentrated in hot spots around the field, but you don’t always know exactly where. This means you have to be consistent and proactive with your insect control strategy. This includes whether you’re choosing a conventional corn hybrid without an insect trait, or choosing a single trait or double trait.

"What we’ve seen over the years with our university testing, is in 10-years of testing we’re getting almost a nine-bushel advantage adding a granular or liquid insecticide on top of their trait," he says. "There’s a couple different things going on there. One, traits unfortunately have seen resistance so all four commercial BT traits have now demonstrated some level of resistance in the field, so they may be getting overwhelmed by high rootworm pressure."

Rootworms are also very adaptive with their habitat preferences. Western rootworms are now laying their eggs in proximity to soybean fields, and Lappin says part of that is due to missed weed control.

"As we have more waterhemp in soybeans, as we have more ragweed, they’re using that as a food source late season and laying their eggs close to that food source. So we’re starting to see now Westerns are laying eggs in soybeans, and in states like Iowa, we’re seeing Northern corn rootworm doing what they call ‘extended diapause’," says Lappin. "They’re laying their eggs in corn, but those eggs are lying dormant for up to 2-3 years."

It’s recommended to start scouting your fields for beetles in mid-June.

Find strategies for corn rootworm control