Should I Be Scouting Fields for Corn Rootworm?

Published on: 15:51PM Jul 05, 2012

Question: Should I be scouting for corn rootworm in my fields at this point, and is there anything I can do if I have heavy populations?

Answer: The corn rootworm hatch has occurred about 30 days earlier than normal due to the warm temperatures this spring. Depending on the planting date of a particular field, rootworm larvae could have been feeding before the Bt protein was fully expressed if you used transgenic hybrids. There are areas across the Corn Belt where we are seeing one to two nodes of feeding from heavy rootworm pressure right now. Also, rootworms that have fed on the protein can have delayed feeding and emergence; this can still have an impact on the crop beyond the current state.

At this point, adults have begun to emerge and feed on tissue and silks as well, which is really a concern for two reasons. The adults are emerging and feeding on the above ground parts of the plants, which could affect pollination. Plus, each adult female will lay approximately 600 eggs that will overwinter and hatch next spring, and that can have an impact on the 2013 corn crop.

The top priority is helping farmers assess their current pest pressure, including the intensity of feeding and the number of corn rootworm adults present. A half-inch of silk is really the magic number; you need at least a half-inch for optimum pollination. So if you are shedding pollen and you have less than a half-inch of silk that’s when you might address the situation. Where needed, consider an application of a foliar insecticide like Warrior II with Zeon Technology or Besiege as a pollination aid and also to prevent adult females from laying eggs for next year.

Answer provided by Craig Abell, Syngenta Crop Specialist.