Soybeans: Solid IPM Plan Needed to Fight Soybean Looper and Corn Earworm

Heavy soybean looper damage. Photo: Justin Ballew, Clemson University

Southern soybean farmers are preparing for another season of insect infestations. Corn earworm and soybean looper have the potential to take the biggest bite out of yields this season. Effective control begins with diligent and frequent scouting and establishing a sound Integrated Pest Management plan to treat yield-robbing pests. 

Scouting and thresholds

When scouting for defoliators such as armyworm, soybean looper or leaf beetle, evaluating each field based on level of defoliation at various points in the growing season is best, says Dominic Reisig, associate professor and entomology Extension specialist at North Carolina State University. For narrow rows under 30 inches, which most Southern soybean growers now plant, he recommends using a sweep net to check several spots in a field.

“The sweep net is really used more for identification to determine which of the defoliator pests are present versus counting the number feeding,” Reisig says. “That’s because our threshold is based more on percent of defoliation of the entire canopy than the number of caterpillars present.”

Reisig explains the defoliation threshold varies by timing within the growing season and is determined by pre-bloom and blooming stages. Soybeans tolerate more insect feeding or foliage loss before blooming.

“Prior to blooming, we can safely say that growers can tolerate 30% foliage loss throughout the entire canopy and not experience yield loss,” Reisig says. “If the plants are blooming, however, or it appears that flowering will occur within a week or so, we recommend 15%  foliage loss as the potential yield-loss threshold. We are confident that if growers treat at these levels they can prevent yield loss.”

Reisig cautions that soybean looper can be tricky to spot. The caterpillars start feeding at the bottom of the canopy and move up so early feeding isn’t easily noticeable. Once they grow larger, they tend to migrate up in the canopy and begin to eat faster as appetites increase.

“Southern soybean farmers should be on the lookout now and remain diligent in scouting for several potentially devastating insect pests,” says Randy Huckaba, field scientist, Dow AgroSciences, Raleigh, North Carolina.

“Many of the Lepidoptera pests have become more difficult to control in recent years due to increasing resistance to several more widely used insecticides,” he said. “Intrepid Edge insecticide has become a valuable tool in farmers’ soybean pest control arsenal.”

Intrepid Edge insecticide combines the knockdown power of spinetoram with the residual control of methoxyfenozide, allowing for faster knockdown and consistent residual control of destructive foliage- and pod-feeding insects, including armyworm, corn earworm, bollworm and looper. The combination of chemistries also makes Intrepid Edge an excellent rotational option for resistance management that serves well as the primary insecticide treatment option for farmers’ IPM programs.

Treatment recommendations and timing

“Generally, we’re waiting to make a treatment recommendation for soybean looper until we’ve reached the defoliation threshold,” Reisig says. “By that time, the caterpillars are usually pretty large. It takes an insecticide like Intrepid Edge that has a fast knockdown and is proven to work well on large caterpillars. The fast knockdown also is important because the larger the caterpillar is, the more, and faster, it is going to eat.”

In addition to the broad spectrum of Lepidoptera pest control, fast knockdown and long residual, Intrepid Edge insecticide will not flare mites or aphids, and minimizes disruption of beneficial insects often caused by other insecticides.

Reisig is especially excited about the fit of Intrepid Edge for soybean looper in his area of extreme eastern North Carolina.

“Soybean looper is a migratory pest here that we experience throughout the growing season,” he says. “The migration piece is significant because we don’t know where the soybean looper is coming from. It likely appears here because it has survived sprays from points to the south. This carries with it resistance implications. I’ve been recommending Intrepid Edge based on the consistency it shows and that we’ve been finding soybean looper populations that appear to be resistant to other classes of insecticides.”

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