Entomology Update: Preparing For Corn Rootworm Issues Back »

Written collaboratively by Ada Szczepaniec (former SDSU Extension Entomology Specialist) and Laura Edwards.

Low temperatures and late planting have delayed insect problems too, but it’s not too early to mention corn rootworms that will likely be a hot topic this summer.

Corn rootworms will probably cause a lot of concerns this summer owing to the increasing incidence of unexpected performance issues of certain Bt corn hybrids. Who should worry about these issues?

If you had a field in continuous corn production for at least three years, used the same Bt hybrid, noticed some evidence of corn rootworm damage such as goose-necking and lodging, and have observed significantly greater numbers of adults emerging last summer, your field is probably in the high-risk category for corn rootworm infestations. Rotation to another crop is the best management recommendations because these insects cannot survive without corn roots.

For a number of producers, rotation is not an option, and they will likely be applying soil insecticides during planting. If you are going to apply insecticides and would like to be a part of an experiment testing their effectiveness, we are teaming up with Extension faculty at University of Minnesota to collect data from producers interested in this experiment. Details of the experimental design can be found in the University of Minnesota's Corn rootworm resistance to Bt ‐RW corn publication. This collaborative effort involves leaving small portions of the field untreated to compare how the pests survive in treated and untreated plots. If you are interested, please get in touch with Ada Szczepaniec at (605) 688-6854 with questions about the protocol.

As I mentioned above, rotation is the best strategy to manage this pest. Because corn is such a profitable crop, however, we try to come up with recommendations that maximize the number of years when corn is grown. Scientists from Iowa, for example, are recommending a 5-year rotation that includes four years of corn.

The rotation plan includes:

  1. Soybeans,
  2. Non-Bt corn
  3. Non-Bt corn plus soil insecticides
  4. Bt-corn hybrid with stacked traits
  5. Bt-corn hybrid with a different combination of stacked traits.

The key benefit of this type of rotation is maximizing the number of years that growers plant corn, and rotating the types of Bt toxins and synthetic insecticides used to manage corn rootworms. It is likely that recommendations for increasing insecticide applications will become more frequent this spring and in the coming years. Increasing insecticide use will increase the probability that corn rootworms will develop resistance to insecticides as well. When this occurs, managing these insects and growing corn will become an economically as well as environmentally costly production. Simply increasing insecticide use is not a sustainable practice and will contribute to even more severe resistance issues in a few years.

Corn Rootworm Management

For more on the biology of these pests and some management recommendations, view the video below.

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