January 30, 2003

The Bean Leaf Beetle: An Emerging Threat to ND Producers?

An increase in the number of soybean acres is causing concern that the bean leaf beetle may become a threat to North Dakota soybean producers.

"The bean leaf beetle has not been a major issue in North Dakota and northwestern Minnesota. However, with the increase in soybean production there is potential for beetles to spread to North Dakota," says Phil Glogoza, North Dakota State University Extension Service entomologist. The beetle is moving closer to North Dakota with infestations reported in southeastern South Dakota and southern Minnesota. Nebraska, Iowa, Illinois and areas south of those states are where the greatest economic loss has occurred from the beetle.

Bean leaf beetles overwinter as adults in plant material located around soybean fields. They become active in the spring when host plants such as alfalfa, soybeans and other legumes become available. Although the beetle may be present in legumes such as alfalfa or sweet clover before soybeans emerge, they are not known to cause any damage to these legumes.

The adult beetles enter the soybean field in the spring. They feed on developing cotyledons and leaves and lay eggs. Once egg laying is completed, adult beetles die. The larva feed on the root and root nodules below ground. The insect develops from egg to adult in 25-40 days. There are two generations per season south of North Dakota. The second-generation adults feed on leaves and pods causing defoliation and scarring.

According to Glogoza, one of the biggest threats of the bean leaf beetle is the disease that they transmit. The bean pod mottle virus causes reduced yield and seed quality. Symptoms include a blistered appearance to soybean leaves, green stems at the end of the season when pods are mature and a mottled appearance on the seed coat of harvested soybean. Confirmation that bean pod mottle virus is present can only be determined by a plant tissue test.

"We are not sure what has kept the bean leaf beetle from establishing in North Dakota," Glogoza says. It is possible the cold winters are keeping the beetles out by limiting their ability to survive. According to Glogoza, the goal is to make producers aware there may be a potential threat and educate them on the signs of infestation so early detection of their presence is possible. So far there are no varieties of soybeans that are resistant to the bean leaf beetle.

Joel Coats, Iowa State University entomologist, and Ken Ostlie, University of Minnesota entomologist, will discuss the topic of bean leaf beetles as an emerging threat at the Advanced Crop Advisers Workshop set for Feb. 20-21 at the Holiday Inn in Fargo. The workshop is designed for agricultural professionals who advise farmers with crop production recommendations. The event is sponsored by the North Dakota State University and University of Minnesota extension services.

For more information on the bean leaf beetle contact Phil Glogoza at (701) 231-7581 or at pglogoza@ndsuext.nodak.edu.

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Source: Phillip Glogoza, (701) 231-7581, pglogoza@ndsuext.nodak.edu
Writer: Deana Oe (701) 231-8371, deana.oe@ndsu.nodak.edu
Editor: Tom Jirik (701) 231-9629, tjirik@ndsuext.nodak.edu