Southeast farmers tackle swift-moving soybean pest
If you grow soybeans in the Midwest, you might have found yourself singing, "Rain, rain go away" more than once this year. But experts in the Southeast say you might be whistling a different tune in the not-too-distant future because of a legume-loving pest that spreads rapidly in the absence of wet weather.
That’s right: The kudzu bug has your address. Known to the scientific community as Megacopta cribraria, the pests feast on legumes including kudzu, soybeans, wisteria and lespedeza.
"Get ready because they’re coming," says Alex Harrell, a Georgia farmer who grows 2,000 acres of soybeans, corn, wheat, grain sorghum, peanuts and watermelons in Lee, Sumter, Dooly and Crisp counties. "Three years ago, we didn’t have them."
Left unchecked, the bugs resulted in a 76% yield loss in one Georgia soybean field, says Dominic Reisig, entomology professor, North Carolina State University. On average, though, untreated kudzu bugs cause 20% yield loss. Putting controls in place can bring that figure to zero.
A population explosion. Kudzu bugs first appeared in 2009 in the U.S., Reisig says. At the time, they were confined to a nine-county section of Georgia near Athens and Atlanta.
"I wasn’t really worried about it," Reisig says. "But by 2010, they had spread over half of Georgia, about half of South Carolina and even part of our state."
Today, the bugs are found in more than a dozen states, adds Jeremy Greene, entomology professor, Clemson University. Geneticists have narrowed the bug’s origins to an eastern country such as Japan, China or India, he says, and they suspect one pregnant female arrived in the U.S. sometime before 2009 to start the entire invasion.
While the bugs were prolific in 2013, they probably weren’t as bad as they could have been because substantial rainfall kept them closer to home. "The states that start with an ‘I’ should be paying attention to a lot of the work we’re doing on kudzu bugs," Greene says.
Scouting and control measures. Adult kudzu bugs are brown and about the size of a lady beetle. The creatures suck the sap out of soybean stems. They don’t consume leaves or feed on seeds or pods, but their indirect feeding can limit seed size and number of pods. The bugs have also been shown to limit plant height without hurting yield.
"They indirectly reduce the plant’s ability to move photosynthate around and fill out seeds and pods," Greene says.
The situation with kudzu bugs isn’t entirely hopeless for soybean producers. For one thing, a limited quantity of the critters doesn’t automatically mean yield loss is occurring.
"We have some pests that defoliate fields in a weekend, but this is not one of them," Reisig notes. Rather than spraying at the sight of one bug, he says, managing planting dates and insecticide applications can go a long way.
Early planted beans are at the greatest risk of damage from the kudzu bug. Female bugs store sperm during the winter and begin laying large quantities of egg masses when conditions warm in April and May, Greene explains. The insect can produce two complete generations in a year, so soybeans planted during this time are at the highest risk because they can be exposed to both generations.
After your crop is in the ground, determine whether an insecticide application is needed using the sweep method. Take between 10 and 25 samples using a sweep net, Greene says. If you average one nymph in your net per sweep, it’s a good idea to consider an insecticide application.
A farmer who plants beans in mid-May, for example, might spray once early in the season and again later to target both generations of the bug. Harrell sprayed three times during the 2013 season.
"I sprayed in bloom, at first pod and then later on after all the pods were on," he says. While the bugs are all over his fields, the good thing is they are easy to control.
You can e-mail Nate Birt at firstname.lastname@example.org.