BOWMAN SC grower Landrum Weathers checks for kudzu bugs in soybeans at his family farm

BOWMAN, S.C., grower Landrum Weathers checks for kudzu bugs in soybeans at his family farm.

Kudzu bug chewing up South Carolina

• It is occurring in such high numbers it doesn’t take a trained entomologist to spot one. In most cases smelling them, not spotting them, is the first contact people get with these Asian imports. • Regardless of their family tree, the kudzu bug is becoming a bigger problem in agriculture as they spread throughout the Southeast.

The kudzu bug came from China, landed in Atlanta, Ga. and in two short years has chewed up a variety of crops in every county in South Carolina, and has made good progress doing the same in North Carolina.

Technically, the kudzu bug isMegacopta cribraria, and is known in most parts of the world as bean plataspids, and in some areas as lablab bugs. The bugs, which look like boxy brown ladybugs, emit a foul-smelling secretion when threatened.

It is occurring in such high numbers it doesn’t take a trained entomologist to spot one. In most cases smelling them, not spotting them, is the first contact people get with these Asian imports.

In Georgia, where they first appeared in high numbers, witnesses have reported being able to smell the stench from their cars while crews are cutting kudzu overgrowth along highways.

The bean plataspid is native to India and China and is found in most soybean production areas of Asia.

The insect is pea-sized, greenish brown, and round with a wide posterior. It appears to waddle when it walks on a surface and is an excellent flier. Its flying ability helps account for its rapid spread across the Southeast.

Its life cycle typically lasts 7 weeks. However, the chemistry of the host plant can significantly affect the insect’s reproductive characteristics — such as fertility and length of generation — as well as its feeding rate, even the impact or level of damage it has on the host plant.

So far, entomologists have been astounded by its rapid movement, mostly north to south, throughout the Southeastern U.S.

Clemson University Entomologist Jeremy Greene says kudzu bugs were found in a handful of counties in his state last year. This year the bugs have been reported in every county in South Carolina.

Greene says the insects are often mistakenly referred to as stink bugs, but are in a different insect family than commonly occurring green, brown and Southern green stink bugs. Regardless of their family tree, the Clemson researcher says they are becoming a bigger problem in agriculture as they spread throughout the Southeast.

Bowman, S.C., grower Landrum Weathers says kudzu bugs came into his soybeans while the crop was still immature. Killing them was no problem, he says, but they kept coming back in bigger numbers after every spray.

The big problem with kudzu bugs in soybeans is getting insecticide to them. They tend to feed on the stems of leaves in the lower parts of the plant and once the soybean canopy covers the rows, it becomes a challenge to get enough chemical to the insects to manage high populations.

Adults and immature insects (nymphs) gather in large groups and suck sap from a host plant, weakening and stunting it. Adults have been observed sucking sap from the host plant’s leaves, stems, budding flowers, and mature green pods. Severe infestations of adults and nymphs feeding on leaf sap can cause extensive defoliation in host plants.

Rapid movement

Since it was first found in and around Atlanta, Ga., in October of 2009, it has spread to all 46 counties in South Carolina and more than 40 counties in North Carolina. Though its movement has been primarily south to northeast, it has also been reported in several counties in Alabama.

In 2010, it was found in only 16 counties in South Carolina and was not found in North Carolina. Greene says there was an extensive checking program in both Carolinas in 2010 and the counties in South Carolina were the only ones in which it was found.

How it moves so rapidly may best be explained by looking at our prevailing weather patterns, Greene contends. From its epicenter, the insects have moved mostly north and northeast, or the path of our most prevalent weather patterns. The bigger question is where will it go next?

Virginia Tech Entomologist Ames Herbert says researchers in Virginia are looking for kudzu bugs, but so far none have shown up in an assortment of traps that are generally accurate at detecting insects, even at low populations.

In its native Asia, kudzu bugs prefer kudzu to crops. However, it is well adapted to wild wisteria and a broad range of host plants commonly found in the Southeastern U.S. Greene says all indications are that this pest will continue to grow and spread and potentially be an economic threat to crops in the Southeast.

Kudzu bugs have proven to be susceptible to a wide range of insecticides, but Greene explains the problem is exactly what Weathers and other growers in South Carolina are finding that late in the season, killing them isn’t the problem, getting the insecticide to the bugs is the problem.

“These bugs are very specific on where they feed on soybeans. They occupy the bottom part of the canopy and feed on the stems and leaf petioles. More mature bugs are often found on the main stem of the soybean plant — very near the ground,” Greene says.

There isn’t much a grower can do to protect late-season beans from these insects. “And, with all the wild hosts available around our soybean fields, there isn’t really much they can do in planning for the 2012 season to reduce pressure from kudzu bugs,” he adds.

A part of the control strategy will likely be to knock populations down as early in the season as possible. “We have seen that well timed insecticide applications can slow down, if not prevent large buildups of these insects later in the season when it becomes more difficult to get material through the plant to the bug,” Greene says.

Early in control efforts

The South Carolina scientist stresses that researchers are early in their efforts to manage this pest, because it wasn’t even known to exist in the Southeast until the fall of 2009. Since its arrival the kudzu bug has definitely grabbed the attention of entomologists at land-grant universities across the region.

Early tests indicate pyrethroid insecticides work well to control these Asian imports. There are subtle differences that researchers are beginning to find with the pyrethroids, but in such a limited time, it’s difficult to know what will work best at different times and under different growing conditions.

Again, early in the research process, Greene says it appears combinations of pyrethroid and neonicotinoid insecticides work better than either one of the popular families of insecticides work alone.

“In early testing Indigo, a combination of neonicotinoid and pyrethroid chemistries has worked well to control these insects,” Greene notes.

This bug is likely to be an economically important pest in the Southeast, but it can be managed in tandem with other pests that occur in crops. That said, the South Carolina entomologist says in many cases there will be specific applications just to control kudzu bugs, and anytime you have a dedicated spray for one insect, it becomes an economically important pest to growers.

There will be a lot of data available once 2011 tests on kudzu bugs is analyzed, and more so than ever, it will be important for growers to attend regional and county soybean meetings. “The more growers know about the insect, the better they will be able to manage it,” Greene says.

One tool he is working on with colleagues in Mississippi is a biological control of kudzu bugs. There is a native parasitoid that is very specific to the kudzu bug. “Obviously, we are early in the process of figuring out possible biological controls, but kudzu bugs do have a number of commonly occurring natural enemies in Asia that may one day be a big part of our control efforts,” Greene says.

In China, kudzu bug is listed as a pest of grain crops, but not as a major pest. It may be that it has enough natural enemies there to keep it in check. In the U.S. with few native enemies, it is just spreading like wildfire,” he adds.

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