Plant Health Initiative

Scouting for the Bean Leaf Beetle

Bean Leaf Beetle. Note the prominent black triangle at the front of the wing covers. This is the most reliable diagnostic feature of the bean leaf beetle. The marking is always present and it distinguishes the bean leaf beetle from other beetles in soybean. Photo credit  Marlin Rice and the ISU Entomology Image Gallery. Also see: Bean leaf beetles and others: correctly identifying the pest, Iowa State University:

Start scouting early in the season. Kevin Steffey, entomologist at the University of Illinois, recommends sharpening your scouting skills for bean leaf beetles in seedling soybeans. Experienced scouts have learned that bean leaf beetles tend to "play dead" and drop from seedling soybeans to the ground when they are disturbed. So approach your sampling area quietly.

Examining plants by hand is the easiest method for seedling soybeans. As the plants grow, use of a beat cloth may help you assess numbers of bean leaf beetles per foot of row. Remember to scout in several areas of a given field to obtain a reasonable assessment of bean leaf beetle density for the field. A few high counts are offset when several areas of a field are not infested, lowering the average number of beetles per plant. There's no need to treat an entire field and spend more money than necessary if the field average of bean leaf beetles is lower than economic thresholds.

The overwintered female beetles usually begin to lay their eggs after colonizing the bean fields. Populations of first generation beetles emerge from these eggs and usually peak in late vegetative (V) or early R stage, generally in early July. Populations of second generation beetles peak during pod-fill stage in August.

Drop cloth method

• Walk 100 feet in from the field edge and scout each field and each variety separately.
• Place a 3-foot wide strip of cloth on ground between the rows.
• Bend the plants on one row over the cloth, and shake them vigorously.
• Count the number of beetles on the cloth.
• Repeat the procedure four times for each 20 acres of the field.
• Determine the average number of beetles per 3-foot of row.
• If the number of beetles is below the economic threshold, sample your fields again the following week, or a third week if necessary.

Sweep net method

• Walk 100 feet in from the field edge and scout each field and each variety separately.
• Take 20 sweeps.
• Repeat the procedure four times for each 20 acres of the field.
• Determine the average number of beetles per 20 sweeps.
• If the number of beetles is below the economic threshold, sample your fields again on following week, or a third week if necessary.
• For suggestions on sweep net equipment, read If you scout soybeans, you need a net in the ICM newsletter.

Adapted from
New Concept for Bean Leaf Beetle Management
Wai-Ki F. Lam, Marlin Rice, Larry Pedigo, and Rich Pope
Integrated Crop Management Newsletter , Iowa State University