Kudzu Bugs Are on the Move in Soybeans

February 28, 2014 02:57 AM
Kudzu Bugs Are on the Move in Soybeans

This new pest landed in southern fields in 2009 and is headed north.

Kudzu, commonly called the "vine that ate the South," has been despised in the region for more than 100 years. Now, soybean farmers there face a new foe with a similar name, the kudzu bug, and the pest has spread rapidly through much of the Mid-Atlantic, Southeast and Mid-South.

While kudzu bugs get their name from the fact that they feed on kudzu, they have a voracious appetite for soybeans as well. They feed on the plants by inserting piercing mouth parts into the soybean leaves and stems to suck the nutrient-laden sap.

"The more bugs in the crop, the poorer the seed weight of your soybeans," says Jeremy Greene, a Clemson University Extension entomologist.

Greene addressed a group of agricultural media about the kudzu bug during the 2014 Commodity Classic. The event was sponsored by Chemtura AgroSolutions, the manufacturer of DoubleTake insecticide.

Researchers first identified the kudzu bug in 2009 in a nine-county area in northeast Georgia. They speculate the pest snagged a ride on a plane to travel from its native home in Asia to the United States.

Its ability to hitchhike has enabled kudzu bug to develop into a significant economic pest during the past four years in states including Alabama, Georgia, Florida, North and South Carolina, Tennessee and Virginia.

Average yield loss for untreated soybeans attributed to kudzu bug has been observed by Extension entomologists at 20% in South Carolina and Georgia, and losses as high as 50% have been reported.

Greene says he wouldn’t be surprised to see the pest show up in parts of the Midwest as it is moving in that direction.

"If it can stand the winters, I think it will eventually be up there," he speculates. "It will be interesting to see how far it can go in those colder climates."

According to information on the website kudzubug.org, the pest overwinters as adults near kudzu patches and soybean fields in southern states on plant debris and behind tree bark, but it will also overwinter in structures such as houses and other buildings.

In spring, the adult pest emerges from overwintering sites and moves into kudzu or wisteria where they mate, lay egg masses, and develop through five nymphal stages before moving into soybeans as adults.

However, Greene notes that kudzu bug can bypass kudzu and wisteria and go from overwintering as adults straight into soybeans.

"They can attack soybeans very early in the season," Greene says.

That ability poses an additional issue for growers in the Midwest who are planting earlier than ever to boost crop yield potential.

"They’ll have to realize they’ll be more at risk with this insect and may need an extra spray dedicated to it," Greene says.

His research shows that pyrethroid-based insecticides provide good control of the pest but that "reinfestation can happen if you treat too early."

Penetration of the soybean crop canopy is critical for effective control.

While the kudzu bug can move throughout a field, it tends to congregate in greater density along field edges. Those areas sometimes need added control measures.
Greene adds that scientists are evaluating cultural control measures, including planting dates and host plant resistance, to address the pest.

Scouting Recommendations

Entomologists recommend that farmers use a 15-inch diameter sweep net when scouting for kudzu bug and use a threshold of one immature kudzu bug per sweep. This suggested threshold, which is recommended on the kudzubug.org website, is based on 2011 field trials where a single, properly timed insecticide application preserved soybean yield. In the majority of trials conducted, Entomologists say nymphs usually appear at about the R-2 to R-3 growth stage. If adult numbers are extremely high (multiple adults per sweep) and soybeans are stressed, treatment should be considered; this is a judgment call but the idea is to avoid bug induced stress on soybeans that are also stressed for some other reason.

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