University of Illinois Extension

University of Illinois Extension

Hort Answers

Insect Damage

Bean Leaf Beetle
Certoma trifurcata

4 (1 = rare 5 = annual)
3 (1 = very little damage 5 = plants killed)

Beans, peas, cowpeas, soybeans and corn

Plants Affected

Identification: The bean leaf beetle adult is 1/4 inch long, yellowish or reddish, with or without four black spots and two marginal stripes on the back. Despite the variability in color and pattern, the adult always has a black triangular spot at the base of the wing covers, behind the "neck".

The adult beetles eat holes in the leaves and pods of beans. They feed heavily on the seedlings and may kill or severely stunt them. The larvae feed on the roots and can cause damage by girdling the stem just below the soil line.

Life Cycle
The adult overwinters, allowing it to severely damage seedlings. The slender white larvae live in the soil.

Peak numbers of beetles occur in late May to early June and then again in August to September. Treat seedlings if defoliation is severe. After establishment, plants can withstand moderate defoliation without suffering a loss in yield. Control even light infestations after pods form to prevent cosmetic damage from feeding scars.

Related Resources
Home, Yard & Garden Pest Guide
Illinois Commercial Landscape and Turfgrass Pest Management Handbook
U of IL - Distance Diagnosis through Digital Imaging
U of IL - Plant Clinic