Scouting for Corn Rootworms

Corn rootworm adult. (WHO-HD)

At this time of the year, crops are still growing and corn cobs are filling but farmers are still at

work checking out their fields to figure out what to do next year.

In Central Iowa, Iowa State Extension Field Agronomist Meaghan Anderson heads out to scout a field of corn plagued by Western corn rootworm.

She says this field has run corn-on-corn for six years, “The longer we’re in corn on corn, the riskier it is that we have a Western corn rootworm population. Those are the yellow beetles with black stripes.”

Western corn rootworm are notorious for developing resistance to Bt traits.

Adult corn rootworm beetles eat corn silk. Corn fields that silk later are more likely to attract the beetles, especially if the silk is brown and dry in the surrounding fields. In this field, Anderson says they do not have much left to feed on so they’re eating corn leaves.

As larvae, the rootworms eat corn roots, “Those are really bad because as they eat off the nodes in those roots, they can potentially be causing 15 percent yield loss per node that’s fed.”

Anderson says next year, the farmer has to plant soybeans, “If there’s not any corn out here in the fields, so if we manage our volunteer corn and we plant soybeans instead. We will starve the larvae and hopefully any population that lays eggs here is going to die.”

She stresses the importance of scouting fields, “Just going out and seeing if you’re seeing a lot of these beetles flying around like we’re noticing out in this field and then maybe digging up some corn roots and checking on them, seeing if there’s a lot of feeding on those. Because you may have a problem you don’t know about, so just because your corn is standing up straight doesn’t necessarily mean you don’t have an issue going on below ground, it probably means you’re lucky that you just didn’t have the weather conditions to blow your corn over.”