Croplink

A new website includes an interactive map of rootworm sticky trap results for both Northern and Western corn rootworms. It provides a public spot for researchers, farmers and companies to report and monitor rootworm population movement. Visit cornrootworm.extension.iastate.edu.

Rootworm populations have begun to increase again in the Corn Belt after flooding in 2015 drowned many larvae. That's concerning, especially since growers must increasingly manage rootworm resistance to Bt traits.

Another concerning trend is Northern corn rootworms appear to be venturing deeper into the I-states, says Nick Seiter, University of Illinois entomologist.

Northern corn rootworms feed similarly to Western corn rootworms but bring a different rotation-resistant variant to the field. In Western corn rootworm, rotation-resistant variants survive by adult beetles venturing beyond corn fields to lay their eggs in surrounding rotated crop fields, such as soybeans, which allow the eggs to hatch into a corn field the following year.

Rotation-resistant Northern corn rootworms prefer to wait out crop rotation entirely by hibernating for one to three extra years before hatching into a field that may have returned to corn, a habit known as "extended diapause."

Knowing which type of rootworm you have in your area is important to management and of great interest to entomologists, Seiter notes.

"That's a big motivation for us to track changes in population trends over time in addition to just the typical motivation of understanding what your rootworm pressure is like and whether or not you need a treatment for it," he explains.

Rootworm trapping extends well into August. Bt-resistant rootworms take longer to develop on Bt corn and, thus, emerge a little bit later than their Bt-susceptible counterparts, which emerge from refuge plants faster, says Erin Hodgson, Iowa State University entomologist. Peak activity later in the season could be a sign resistance is an issue.

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-- Iowa State University Corn Rootworm Extension: cornrootworm.extension.iastate.edu

-- Emily Unglesbee contributed to this article.

-- Follow the latest from Pamela Smith, Crops Technology Editor, by visiting the Production Blogs at dtnpf.com or following her on Twitter @PamSmithDTN.

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