Bean Leaf Beetles

Published: June 13, 2008

Reports of bean leaf beetle damage to soybean continue to be reported. Most reports come from areas where soybean fields are few in number and beetles have congregated in fields which have been planted. This small quarter-inch-long beetle ranges from tan to red in color and usually has black spots near the midline of the upper back. It may occasionally lack the black spots, but will always have a black triangle located just behind the head. Bean leaf beetle adults chew oval holes in leaf surfaces, but usually do not chew through larger leaf veins or ribs. In most years feeding damage to soybean seedlings is not economic unless cool, drought conditions slow plant growth and high beetle numbers totally defoliate and often kill the seedlings. This year high numbers of beetles can be found in some early planted fields. Heavy defoliation of seedling plants can cause heavy plant mortality or cause destruction of primary growing points. Many fields have required an insecticide application as they exceeded the economic threshold of 5 or more beetles present or 1 or more plants destroyed per foot of row. Damage may also occur later in the season when second generation bean leaf beetle adults feed on soybean pods. The following is a list of recommended insecticides for rescue of soybean seedlings from bean leaf beetle.