By Erin Hodgson, Department of Entomology and Adam Sisson, Corn and Soybean Initiative
There were several reports of lightning bugs (fireflies) throughout the state last week. Some people correlate fireflies with corn rootworm larval hatch in the Midwest. Based on conversations with Marlin Rice, former ISU entomologist, and Mike Gray, entomologist from University of Illinois, they believe these events are unrelated. Instead, corn rootworm hatch predictions are more accurately based on temperature accumulations.
Research shows about fifty percent of corn rootworm larvae will hatch from 684 to 767 accumulated growing degree days (base 52 F). The map below displays the number of accumulated degree days from Jan. 1 to May 25 for Iowa. Corn rootworm hatch should be happening in the southeast part of the state. Other parts of the state should experience larval hatch in the next 7 days.
Accumulated growing degree days (base 52 F) in Iowa from Jan. 1 — May 25, 2010. Fifty percent corn rootworm hatch is expected to occur between 684 and 767 degree days. This map was created by Iowa Environmental Mesonet, Department of Agronomy at Iowa State University.
Ideally, every corn field should be inspected for corn rootworm larvae after reaching 50 percent hatch. Non-Bt fields are most susceptible to larval damage and should be considered a priority. Continuous Bt corn fields with previous damage should also be scouted. Sample for larvae by digging up corn plants and washing the roots in a bucket; larvae should float to the top of the water. Sample corn plants in different areas of the field to estimate infestation levels.
Corn rootworm damage on the roots of a corn plant
Larvae of the corn rootworm (Photos by Marlin Rice)
Erin Hodgson is an assistant professor of entomology with extension and research responsibilities. She can be contacted by email at firstname.lastname@example.org or phone (515) 294-2847. Adam Sisson is a program assistant with responsibilities with the Corn and Soybean Initiative. Sisson can be contacted by email at email@example.com or by calling (515) 294-5899.