As invading kudzu bugs spread, scientists and farmers plan counterattack
The good news is, we can kill them.
The bad news is, it'll cost us.
And the damage they do in the meantime will cost even more.
Kudzu bugs, first discovered northeast of Atlanta three years ago, have swept through Georgia and the Carolinas. The invading Asian insects leave destruction in their wake — especially to soybeans, a staple crop for farmers.
"They've already become an economic pest on soybeans in the areas they've infected. They're fast-moving and can have a significant impact on a crop," said Jeremy Greene, a Clemson University Research/Extension entomologist who is leading the charge to fight back. "Fortunately, we've learned a lot about them in a short time. It's important for us to assess what we know and formulate the best response for the future."
For that reason, Greene hosted a national conference at Clemson's Edisto Research and Education Center in Blackville, S.C. this week, drawing agricultural scientists and farmers to plan the counterattack.
While crop pest experts intend an aggressive assault, no one is under the delusion it will be an easy fight.
"The word 'eradication' is not being used with the kudzu bug," said Steve Cole, director of the plant industry department in Clemson's regulatory services division, which oversees efforts to monitor invasive species in South Carolina. "The best we can hope to do is find a suitable method of control."
Scientists have come up with insecticides that kill swarms effectively, minimizing the damage the bugs cause to soybean harvests — which tests show average more than 4 bushels an acre on a crop currently selling for about $17 per bushel.
But the insects reproduce in such large numbers and move about so freely, timing pesticide sprays is a tricky business.
"Our problem isn't killing them. We can do that pretty easily," entomologist Phillip Roberts of the University of Georgia told the group at Edisto. "Our problem is minimizing the number of (insecticide) sprays necessary to reduce the damage to a crop."
So far, scientists are finding that kudzu bugs will produce two generations per year in the United States — one in the spring or early summer, another in the late summer. During winter, the bugs try to find a nice, warm place to hide. A hidden corner in human homes is among their favored places, but a barn, outbuilding or underneath the bark of a tree will do.
For that reason, good timing is essential for insecticide sprays and crop planting. If your timing is off, you may kill the bugs in one field only to have others swarm in from nearby.
"It's the early infestations we're worried about now," Greene said. "We're studying them to get that application timing down just right."
Since appearing in northeast Georgia in 2009, the Asian bugs now blanket the Southeast from Florida, north to Virginia and west to Alabama, with pockets of infestations reported in counties in Tennessee and Mississippi. The insect seems to reproduce and spread as efficiently as that other Asian transplant from which they get their name — and on which they feed — kudzu.
"It will probably spread and survive anywhere kudzu survives," Joe Eger of Dow Agrosciences told the conference. He then pointed to a map showing kudzu's range — from Texas and Nebraska to New York and Massacussetts. "It's found almost anywhere kudzu is found, so I suspect it will go much farther north," he said.
This is what draws special interest from the U.S. Department of Agriculture. If the kudzu bug is capable of following its namesake into the eastern plains and the upper Midwest, it can press into the heart of American soybean production.
The bug is bad enough in South Carolina, with 350,000 acres of soybeans that bring in more than $100 million a year, according to the National Agricultural Statistics Service.
But that's a drop in the bucket nationally. The entire U.S. soybean crop was worth $35.7 billion last year, the service reported.
The kudzu bug — named for its affinity for the creeping vine that has enveloped much of the South — is technically a bean plataspid, which is related to stink bugs. It can secrete a foul-smelling chemical that immediately identifies it. Some people are sensitive to the secretion, making it a medical problem as well as a homeowner nuisance and economic pest.
The bean plataspid feeds on juices of legumes, pod-bearing plants that include kudzu, soybeans, peanuts, alfalfa and clover, among others. For reasons scientists don't understand — but for which they are grateful — it seems to leave peanuts alone.
Although the bug likes the taste of kudzu, it doesn't require it.
"They don't have to build up on kudzu to move to soybeans. They can overwinter elsewhere and move directly to a bean crop," Roberts said. "That's why we have to get our timing and chemicals right. As long as the kudzu bug's migration is occurring, we can get a re-infestation."
The word "infestation" often is overused when people talk about insects. Not so with the kudzu bug. Without pesticides to protect it, a single soybean plant will harbor dozens of the critters. During the field day in his Edisto meeting, every leaf in Greene's untreated test plots revealed clusters of the bugs.
"These things have tremendous reproductive potential," said David Buntin of the University of Georgia's Griffin research station. "If you're in an area where they have just moved in, you better hold onto your hat."
"They feed on the vascular fluid of the plant, primarily at the stems," said Clemson doctoral student Nick Seiter. "They're not actually feeding on the beans. They like the thick stems and they leave lesions you can easily see. These lesions put a great deal of stress on the plants and can lead to some pretty severe yield losses."
Test plots at Edisto and Griffin averaged an 18 percent yield reduction from the pests. Some fields were untouched; others lost as much as 50 percent of their yield as the plants set fewer pods with fewer, smaller beans.
The kudzu bug already has caused an international incident.
"Honduras found seven dead kudzu bugs in a poultry shipment from Georgia. They stopped all agricultural shipments from Georgia, the Carolinas and Alabama for a time," Eger said. "Argentina and Brazil are big soybean producers. They are watching what we do carefully."
In the long term, USDA Agricultural Research Service scientist Walker Jones of Stoneville, Miss., believes that a tiny parasitic wasp may help reduce the bug's explosive population growth.
Native to Asia like the kudzu bug and kudzu itself, the wasp eats the kudzu bug's eggs, and not much else.
"Our native stink bug egg parasitoids do not attack the kudzu bug. That's unfortunate," Jones said. "But our research shows that, of all the parasitoids we studied from Asia, P. saccharalis is the only one that attacks the eggs of kudzu bugs and nothing else. I've never been so lucky."
Jones expects to petition USDA next year for permission to begin releasing the tiny wasps. He believes they may be effective at reducing the number of kudzu bug eggs by as much as 73 percent, according to studies conducted so far.
In the meantime, farmers face trying to strike a balance between the cost and timing of insecticides and the damage caused by a new, hungry, invasive pest.
"Will yield increases offset the cost of the spray? That's the decision farmers will have to make," said Ron Smith, an Auburn University entomologist. "With $17 (per bushel) prices, you'll see more sprays than at $7."
"We can control them," Greene said. "It will take discipline. It will take patience. It will take more research to properly define what we're dealing with and how to respond."