Bean leaf beetles are still extremely abundant in some fields and are continuing to cause damage to pods. I swept one field south of Ames on September 8 that was just beginning to turn yellow. In 10 sweeps I collected 229 bean leaf beetles, or as best as I could count! In an adjacent variety where approximately half of the leaves were yellow, I collected 82 beetles in 10 sweeps. It was not uncommon for 60-70 percent of the pods on the upper half of the plants to be heavily scarred or flat with no developing seeds.
I also saw an airplane spraying a soybean field on September 7 and I assume that it was for this insect, which is unfortunate. A majority of the damage has been done at this point in the growing season. Sure, more yield loss will occur in those fields that have not been sprayed, but one of the principles of integrated pest management when using an insecticide is to apply it in a timely manner so that the maximum benefit can be gained from the application. Most fields in Iowa should have been sprayed during mid-August, not early September.
This article originally appeared on page 173 of the IC-484(22) -- September 18, 2000 issue.