A commonly asked question during the past 2 weeks has been, How long will the overwintered bean leaf beetles still be in the fields? Populations normally start to drop dramatically after mid-June and by June 20-25 beetles are often very hard to find. I checked plots at Nashua in northern Iowa on June 13 and densities ranged from zero to five beetles per 3 feet of row, so they can still be found. If you are finding bean leaf beetles in your fields, it is too late to be managing these overwintered beetles. Most of the female beetles will have laid their eggs by now and most of the serious feeding injury has been done. Also, it is too late to manage the beetles in an attempt to suppress the spread of bean pod mottle virus. In early July the first-generation of bean leaf beetles should start to emerge from the soil in soybean fields in southern Iowa. At that time, I will discuss management options for the next population, which is the first generation, of this pest.
This article originally appeared on page 115 of the IC-488(14) -- June 24, 2002 issue.