Although the early April freezing temperatures that dropped below 20 °F probably had little effect on black cutworm eggs (see last week's article ), reports from the field suggest that alfalfa weevil larvae may have been hit hard by the cold temperatures. Kyle Jensen (Lewis), Mark Carlton (Albia), and Virgil Schmitt (Muscatine), all extension field crops specialists, stated in an April 23 teleconference that no live alfalfa weevil larvae have been found in fields that they inspected. Most plants were brown and dead from the freeze, so any larvae that had hatched would be in the terminals and exposed to the cold. Likewise, Kevin Steffey, University of Illinois Extension entomologist, reported last week that in south-central Illinois, his colleagues "found many dead (brown and shriveled) third instar alfalfa weevils in an alfalfa field in Montgomery County, and it's likely that freezing temperatures caused the mortality."
All of this suggests that alfalfa weevil problems may be minimal this spring, especially in fields where larvae hatched. However, some larvae may not have hatched, so fields should still be scouted, especially in central and northern Iowa.
Marlin E. Rice is a professor of entomology with extension and research responsibilities in field and forage crops.
This article originally appeared on page 120 of the IC-498 (7) -- April 23, 2007 issue.