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Corn Earworms/Bollworms Continue to Plague Soybeans
Author: Gus Lorenz, Extension Entomologist

Bollworms in soybeans continue to be a problem across the state. This is undoubtedly one of the biggest bollworm outbreaks in a long time. Pressure has been constant now for the last three weeks and has spread to the farthest corners of the state. Some areas have much higher numbers than others, but finding treatment-level bollworms is not a problem if you know where to look. The worms continue to be the worst on fields that are blooming and/or beginning to set pods and have not achieved lapping or canopy closure, although it seems like we are getting more reports of treatment-level on fields that are already lapped or even fields that haven’t started blooming yet. While I think most folks are aware of the situation, if you’ve missed earlier postings, I continue to get reports of pyrethroids not achieving an adequate level of control.  It’s even worse in milo. We are paying the price for cheap pyrethroids now and the indiscriminate use those cheap prices brought. 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.  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.
  2. Consider 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.
  3. Scout fields closely following application to make sure adequate control was achieved and for subsequent problems with bollworms and other pests.

We don’t expect bollworm levels to lighten up for a couple of weeks so you will have to continue scouting closely for them. We are beginning to see quite a few loopers in fields to the south so be watching for developing populations of this pest. We are also seeing increasing stink bug numbers in early-planted fields with brown stink bugs appearing predominately in many of these. Bifenthrin (Brigade, Fanfare, Discipline, Sniper, Tundra, etc), Acephate (Orthene, Bracket), and Endigo are the products of choice for brown stink bugs.

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