By Adam Sisson, Corn and Soybean Initiative and Erin Hodgson, Department of Entomology
NOTE: This article was retracted on May 4, 2010 - due to new information and data. See the correction article.
Now is the time to scout for alfalfa weevil larvae in most crop reporting districts in Iowa. The scouting threshold has not yet been reached for northern and west central districts of the state but scouting dates are coming up quickly.
Growers in the southern three districts should start scouting for larvae at 200 growing degree days (using a base of 48 F), while those in the central and northern regions should start scouting at 250 growing degree days. This means that growers should presently be scouting fields in southern and most of the central districts of the state. Scouting for larvae should begin May 4 in the west central district and May 7 for all three northern districts of Iowa (Figure 1).
Figure 1. Alfalfa weevil scouting dates and accumulated growing degree days (using a base of 48 F) in Iowa from Jan. 1 to May 2, 2010.
Scouting, identification and economic thresholds for treatment of the alfalfa weevil are explained by Marlin E. Rice in a past ICM Newsletter article.
Adam Sisson is a program assistant with responsibilities with the Corn and Soybean Initiative. Sisson can be contacted by email at firstname.lastname@example.org or by calling (515) 294-5899. Erin Hodgson is an assistant professor of entomology with extension and research responsibilities. She can be contacted by email at email@example.com or phone (515) 294-2847.