May 26, 2011

Q: With $7 corn, what's the threshold for treating black cutworms in corn?

A:  Bob Wright, extension entomologist: The Iowa State University newsletter had an article on black cutworms earlier this month that made the following suggestion:

Thresholds

If larvae found in the field are smaller than ¾ inch, then a threshold of 2 to 3 percent wilted or cut plants indicates an insecticide application is warranted. If larvae are longer than ¾ inch, the threshold increases to 5 percent cut plants. Remember to take into consideration the plant population in a particular field and adjust threshold numbers accordingly. However, with corn price and input fluctuations, a dynamic threshold may be more useful.

An ISU Excel spreadsheet allows you to input your scouting data and use their calculations to aid management decisions regarding black cutworm.