Bean Leaf Beetles and Seedling Soybeans

May 28, 1999
Now that soybeans have emerged or are emerging throughout Illinois, bean leaf beetles, which have been active for at least a month, are leaving alfalfa fields and colonizing soybean fields. The beetles will feed on soybean seedlings, and the females will lay eggs in the soil to begin the next generation. As growers keep watchful eyes on their emerging crops, some may overreact to seedling defoliation. We have indicated for at least a couple of years that recent research findings suggest that our old thresholds for bean leaf beetles were too low. The new thresholds, based on solid research from the University of Nebraska, indicate that at least 16 beetles per foot of row during the early seedling stage of growth or 39 beetles per foot of row at soybean stage V2+ are necessary for economic damage.

If the density of bean leaf beetles in a soybean fields exceeds one of the aforementioned thresholds, an insecticide may be warranted. The following products are suggested for control of bean leaf beetles in soybeans: Ambush 2E* at 3.2 to 6.4 oz per acre; Asana XL* at 5.8 to 9.6 oz per acre; dimethoate (see labels for rates of application; several formulations are available); Lorsban 4E at 1 to 2 pt per acre; Penncap-M* at 2 to 3 pt per acre; Pounce 3.2EC at 2 to 4 oz per acre; Sevin XLR Plus at 1 to 2 pt per acre; and Warrior T or 1E at 1.92 to 3.2 oz per acre. (The use of products followed by an asterisk is restricted to certified applicators.)--Kevin Steffey

Author: Kevin Steffey