Soybean bug of the year
If North Carolina State University entomologist Dominic Resig were giving out awards, the trophy for the insect with the most impact on soybean producers last year would have to go to the kudzu bug.
Until last year, that is a name you might not have ever heard of before — but the kudzu bug, otherwise known as the Megacopta cribraria, bean plataspid, or lablab bug, is a bug you’re likely to be hearing about many times in your future.
For the record, until its recent appearance the kudzu bug had never been seen in the United States, but researchers have discovered it is widespread throughout Japan, China, Indonesia and parts of India.
It was first found in the United States in 2009 in Athens, Ga., but since then has quickly spread throughout not only a large part of that state, but throughout a number of surrounding states, including South Carolina and 50 counties in North Carolina. It gets around, mainly because of the widespread nature of its favorite host, the irrepressible kudzu weed. The kudzu bug is a strong flier — and apparently a good hitchhiker, too.
• A new spreading pest, the kudzu bug, made its presence felt in soybeans in 2011.
• Careful management can help farmers control this pest.
• Researchers expect it to continue to spread at a fast pace in 2012.
“In soybeans we are worried about the second generation of this kudzu bug,” says Reisig. “We think the first generation builds up on kudzu and perhaps other wild legumes. Then it goes into a host shift and over a period of several weeks it flies into soybean fields.”
The kudzu bug looks to some somewhat like an overstuffed stinkbug, and Reisig says the two, although not in the same family, are distantly related. They are “cousins,” so to speak.
The kudzu bug and the stinkbug have similar mouthpart structures. The kudzu bug can also emit an odor, described by one South Carolina entomologist as a cross between a cleaner and an industrial solvent. It is said the emissions that cause this smell may be able to stain and even blister the skin.
What to expect
When kudzu bugs attack a field, a farmer might first see a few of these insects on the field border, but then they move deeper into soybean fields. Sometimes this move can take place so quickly, Reisig notes, it can seem “overwhelming to a farmer, with massive amounts of adults flying around.”
Georgia researchers report that last year they were picking up as many as 2,400 insects per 20 net swoops. That is a worst-case scenario, Reisig says.
There is a silver lining with the kudzu bug, however. Stinkbugs, for example, feed directly through the pod into the bean, itself. But the kudzu bug does not feed on the bean, which is obviously the most important part of the plant from the farmer’s point of view. Instead the kudzu bug feeds on the veins of the plant, sucking up nutrients, sugars and water.
“Because it is a more indirect damage to the plant, we can actually wait awhile before we treat,” Reisig says. “From the research that we have, we think maybe it is best to wait until all the adults arrive into the field, mate, lay their eggs and wait for a few of those eggs to hatch out into nymphs — and then spray.
If you spray too early, you may kill some adults coming in, but then more of the adults will move in from the kudzu and overwhelm the soybeans again. Then you will have to spray again. So I guess it is a blessing in some ways in how it feeds. On the other hand, it certainly can seem overwhelming to see hundreds of insects feeding on a plant, especially when I am here telling you not to do anything about it.”
Checking out the arsenal
Not every pesticide chemistry has been screened, but quite a few of them have. “We’re telling farmers to go out into the field and use a sweep net. When they find one nymph per sweep, then it is time to treat,” Reisig says.
The best insecticides that have been tested are those that have a high rate of bifenthrin. Some examples are Hero, Brigade and Brigadier (which has bifenthrin along with some additional chemistry in it). There are a number of generic bifenthrins, such as Sniper and others, and these are recommended, too.
Reisig notes Endigo is recommended as a “pyrethroid with some additional chemistry mixed into it — and that seems to be better than a pyrethroid alone.”
Reisig notes some growers reported using three pesticide sprays in 2011 to handle the bugs. Again, because of the indirect feeding damage, he thinks they could have waited longer. Based on trials last year in Georgia and South Carolina, researchers found if they treated at the time nymphs are present, they could get away with one treatment a year and still preserve yield.
“So from that perspective, it looks like if we spray at the right time, we might be able to control the pest,” Reisig says. On the other hand, Reisig notes that this pest is new to all of us, so at this point no one really knows what its full potential for damage might be.
The reality and the potential
“I see North Carolina as the tipping point,” Reisig says. “There is less kudzu in parts of North Carolina than in Georgia or South Carolina; however, we have a whole lot more soybeans in North Carolina. Georgia for example, had 150,000 acres of soybeans last year, and North Carolina had between 1.4 and 1.5 million acres.
“So what is that going to do to a population? I’m not sure. Is that going to make it worse or better? I don’t really know. I’m not sure if we are going to see the same thing, or something different.”
He adds that indications from last year lead him to think the kudzu bugs will continue to spread.
“I think what we are going to see in North Carolina is what they saw in South Carolina last year, which is all of our counties will have kudzu bugs, at least on kudzu, and a lot of them will be on soybeans. We’ll be really struggling with it. And I do think it is going to be moving up into Southern Virginia as well.”
This article published in the March, 2012 edition of CAROLINA-VIRGINIA FARMER.