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Bollworm Blowout Continues and Worsens While Loopers Start Their Move
Author: Gus Lorenz, Extension Entomologist

I know you are getting tired of the bollworms/corn earworms wearing out the soybeans, but unfortunately, the news keeps getting worse. Either you are seeing right now, or will soon, the biggest population of the year. I suspect many will walk into soybeans this week and wonder where all the worms came from. For some, it may be towards the end of the week but be advised; you need to be scouting fields closely. With the kind of numbers we are experiencing this time, no fields should be considered safe from this flight of bollworms. Obviously the beans at the highest risk are those that are late planted, not lapped and just beginning to bloom and set pods. However, with this big a flight, even lapped beans may have problems. Suffice it to say, check every field.

To remind everyone, the following is a list of recommendations to help achieve control:

Suggestions for Bollworm Control in Soybeans

  1. To insure adequate application, we recommend a minimum of 5 gallons per acre (GPA) by air and 10 GPA by ground. Also, consider the addition of an adjuvant, such as crop oil, with your insecticide application. For high populations (2X threshold or greater) if using a pyrethroid, consider adding 0.5 lb/ A of acephate. Tank mixing the pyrethroid and acephate should improve both residual and percent control. Maintain a higher-end rate with the pyrethroid or in other words, don’t cut the rate. We continue to get reports of good control with this tank mix. The tank mix appears to be providing control for 7-8 days before bollworms are at treatment level again where pressure is constant. Avoid this treatment if soybean loopers are also in the field, as it will not provide adequate control.
  2. Consideration should also be made for other insecticides. We have observed excellent control with both Belt at 2 oz/acre and Steward at 1 gal/20 acres. The advantages to these products are that they both provide good control of caterpillars in soybeans, and they have little impact on beneficial insects. However, for the same reason they don’t impact beneficial insects, they also provide no control for stink bugs and other non-caterpillar pests of soybean. Based on our observations, these products have provided the most consistent control of bollworms.  Belt appears to be providing control for 14-18 days before bollworms are at treatment level again where pressure is constant. Also, with soybean loopers coming in from the south, these products will provide control of both caterpillar pests.
  3. Scout fields closely following application to make sure adequate control was achieved and for subsequent problems with bollworms and other pests. With the numbers we are seeing, it will be important to evaluate treatments to make sure we have reduced numbers below threshold. Just remember you need to allow at least 3-4 days behind pyrethroid + orthene or Steward applications and 4-5 days behind Belt applications to determine success. Any earlier and you risk not getting a true picture of how good the application did for control.
Bollworm/Corn earworm

Bollworm/Corn earworm on soybean

Loopers and Saltmarsh Caterpillar

Loopers have started moving into the state now, and many fields have been treated in the southern end of the state. Options for control include Belt, Intrepid, Steward and Tracer. Pyrethroids and orthene should not be considered for treatment of soybean looper. We are also seeing saltmarsh caterpillar (SMC) in many fields. Intrepid is considered the standard for control of SMC. Belt should do a good job, but we just haven’t had the chance to evaluate it yet. Remember our thresholds are the same for all defoliators, 25% defoliation after bloom. Also, loopers have a bad habit of starting at the bottom of the plant and working their way up, so when you see them in the top of the plant you have missed them so no windshielding is allowed.

Stink Bugs

As the earliest fields begin to mature, stink bugs are showing up. Numbers are not outrageous. The problem becomes when you need to treat for stink bugs and loopers. Tankmixing a pyrethroid and something else for the loopers is required and it gets costly.

Trust me, I know we are all getting a little tired of this growing season with the heat and the overwhelming insect problems, but our growers have worked hard up to this point to make a crop, so let’s don’t let the insects take it now.

Saltmarsh caterpillar

Saltmarsh caterpillar


Soybean looper

Soybean looper



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