A new insect is invading Georgia soybeans.
Named the kudzu bug by Phillip Roberts, University of Georgia Extension entomologist, and his colleagues, Megacopta cribraria is native to China and other parts of Asia. Also called the bean plataspid, it was first spotted on Georgia kudzu plants in 2009. By last summer, infestation had grown to soybean fields in 22 counties and in 78 counties overall on soybeans and kudzu.
“Soybeans appear to be very attractive to the bug,” says Roberts, who has followed the menace’s migration since their initial report in parts of the Peach State. “We observed high infestations in soybean fields during 2010 when no kudzu patches were in sight.”
Roberts, who is spreading the word on the new pest at regional grower meetings, tells Corn & Soybean Digest that the kudzu bug appears to feed on the main stem of plants. “They feed on plant juices with their sucking mouthparts,” he says. “We didn’t observe them feeding directly on the pod itself, like a stink bug does.”
He says the infestations may stress bean plants and cut yields by up to 50%, based on data from infestations in China. First-year Georgia field tests show up to a 23% reduction in yields.
High bug numbers significantly reduced pods per plant and beans per pod in University of Georgia entomology research analyses, Roberts says. (The research, conducted by David Buntin and John All, was on soybeans grown in field cages either infested or not infested with kudzu bugs, says Roberts.)
“We have yield data from six trials, and the mean yield loss in untreated plots compared with multiple applications of a common insecticide was 19%, with a range from 11% to 23%,” he says.
Roberts says it’s too early to know an exact threshold requirement for treatment of the new bug. However, he suggests growers treat at an infestation rate of three to five bugs per plant, based on research conducted in China.
“We did not evaluate thresholds in Georgia production systems during 2010. Rather, we focused on first determining the economic pest potential of the bug,” he says. “Yield differences were only significantly different in a single trial, but there is definitely a trend for yield preservation in treated plots.”
Fortunately, some insecticides commonly used to control other soybean pests appear to be effective on kudzu bugs, says Roberts. Good control was observed with various active ingredients at normal use rates, he says. “But we’re not sure of optimal timing of applications to maximize returns.”
He says the challenge may be the re-infestation of bugs following treatments. “We need additional work on thresholds and a better understanding of migration patterns, such as re-infestation following insecticide applications.”
When glyphosate resistance was first discovered on weeds in beans, corn and cotton in Georgia five or six years ago, there wasn’t a true indication that it would spread elsewhere. But it did. Roberts says growers should be prepared for a similar migration of kudzu bug.
“The bug appears to be an active flyer and is attracted to light-colored (especially white) objects,” he says. “Based on our sampling of kudzu and soybeans, the bug has greatly expanded its range in Georgia and the Southeast (including into two counties in Alabama).
“We know that it’s a tropical and sub-tropical species that will likely only be able to establish in the southern half of the U.S. We will know much more after another year of experience.”