Cutworm Problems

Cutworms Chewing Through Technology by Christian Krupke and John Obermeyer

• Cutworms are abundant, especially where weeds were plentiful before planting

• As predicted, seed insecticides and/or Bt corn are NOT controlling severe infestations

Numerous reports have been received of emerging corn being damaged by cutworms. As mentioned in previous Pest&Crop issues (#4, 5, 6, 8) the seed-applied insecticides and/or Bt traited corn will only provide suppression of cutworms. With the severe damage some fields are reportedly receiving, it is obvious that some producers did not scout fields after emergence to determine the need for rescue foliar insecticides.

Black cutworm is not the only species of cutworm present and damaging fields. Many reports of claybacked cutworm have been received as well. This species overwinters as a partially grown larva, so it is larger when the corn is emerging, compared with black cutworms, which begin their annual Indiana cycle as eggs in the spring. What’s important is that larger larvae, ≥ 0.5 inch, are not controlled by Bt proteins expressed in Herculex and SmartStax. Producers are unhappily finding out that black cutworm is the only species labeled for control with these traited-seeds, and rescue treatments are on their tab. And As we’ve learned in the past and hearing again this spring, the seed-applied insecticides (e.g., Cruiser, Poncho) provide only suppression of cutworms. They likely do a fine job of suppressing light to moderate infestations, but severe infestations are NOT controlled, even by the higher rate.

Cutworm control may be needed if 3-5% of the seedlings have obvious foliar feeding and/or plant cutting and live larvae can be found while digging around damaged plants. Higher label rates of insecticides should be considered if the soil surface is crusty and most cutworm activity is below ground. For a listing of foliar insecticides for rescue control, refer to “Corn Insect Control Recommendations – 2011,” which can be viewed by clicking this link.

If you have questions or for more information, please contact Christian Krupke or John Obermeyer in the Department of Entomology.