Time to Scout for Corn Rootworm Larvae

June 17, 2009

By Erin Hodgson and Jon Tollefson, Department of Entomology

Reports from neighboring states have indicated corn rootworm larval hatch for 2009. June 6 has been considered an average hatch date in Iowa, so first and second instars should be actively feeding if present. This is the time to apply a rescue treatment for corn rootworm, and scouting will help determine if action is necessary.

There have been reported failures of Bt corn in Iowa, so we recommend scouting every field every year to ensure root protection. Of course Bt fields require a refuge, and that is where larvae are more likely feeding. If an average of one or more larvae per plant is found, a rescue insecticide should be considered.

There are limited products registered in Iowa for corn rootworm larvae after corn emergence (Table 1). Follow label directions and pay attention to spray guidelines. Post-emergent insecticides applied after the end of June will not be as effective because most of the root injury will have occurred already.

Table 1. Labeled post-emergent insecticides for corn rootworm larvae.

larvae chart

* Restricted use pesticide.
Ω Please see ICM News article on Furadan and residues for 2010
  and beyond.

Three additional resources that may be of interest for corn rootworm management are:
The Corn Rootworm Home Page
Interactive Node-Injury Scale
Evaluation of corn rootworm hybrids

Erin Hodgson is an assistant professor of entomology with extension and research responsibilities. She can be contacted by email at ewh@iastate.edu or phone (515) 294-2847. Jon Tollefson is a professor of entomology with responsibilities in research and extension. He can be reached at tolly@iastate.edu.

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