Source: NCSU COOPERATIVE EXTENSION, 8/16/20


Did you know that corn earworm (CEW) is our most important insect pest of soybean? It’s August, so NC State Extension Specialist Dr. Dominic Reisig tells us about CEW management in this short video.

August is time to scout for CEW in soybeans. They don’t show up in every field every year, so it is important to scout and treat only when necessary.

Scouting tools include a sweep net and a drop cloth.

Sweep nets are best for narrow row beans, planted at less than 30” spacing. We typically use a drop cloth in wide row soybeans, 30″ or greater. But drop cloths are also helpful when using a sweep net, to more easily sort through the contents of your sweep. If you also grow cotton, having a black drop cloth is optimal, but if you do not grow cotton, a light-colored one is fine.

Thresholds vary depending on the cost of control and what the crop is worth. In 2020, our CEW threshold is about 5 corn earworms in 15 sweeps, where a sweep counts as one sweep of the net. CEW can be very destructive to our crop by feeding directly on the pods, so it’s important we treat them, but it’s important we don’t spend money when we don’t have to.

When we’re sampling corn earworm we want to make sure we’ve hit the threshold before making a treatment decision. We have good beneficial insects that’ll take care of populations, and we even have diseases of the pest that will sometimes wipe populations out.

Be sure to check double-crop beans and any later planted beans. They love to lay eggs when soybeans are flowering so it’s very important we catch those infestations as we’re entering R3, and make treatment decisions anywhere from R3 to R5.

If we do hit the threshold it’s important that we use the correct insecticide of choice. Fortunately, in soybeans we have some very good products including Intrepid Edge, Steward, and Tracer. We have another good product known as Besiege or Prevathon. While it’s effective for corn earworm, we want to avoid using it in soybean so that we can preserve its use in cotton where we have many fewer insecticide options. Avoiding overuse of Besiege and Prevathon will delay the development of pest resistance and will help farmers of all of the crops affected by CEW.

Our Online Threshold Calculator is dynamic and includes the cost of control as well as the cost of soybean. For more details and photos of corn earworm visit our Corn Earworm page.

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