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Cotton Insect Update
DR. SCOTT STEWART
JACKSON, TENN.
Other than a few calls about slugs, thrips are the primary pest of concern. Although there seems to be a lot of excitement out there, I’m not seeing anything too out of the ordinary. Thrips populations seemed to have peaked, and some of the earlier cotton is past the window of concern. Considering some challenging weather conditions in mid-May, I’m generally pleased. There have been a few questions that I would like to address.
I sprayed and my thrips populations are just as high as they were a few days ago … what gives? This is pretty common, especially when applications are made as populations are on the rapid increase. Rainfall with 6-12 hours of application doesn’t help. Although the level of control may look bad, there is good news. You’ve taken pressure off the plants for a few days and typically added a node. This makes them less susceptible to thrips. I see the same rebound of populations in my trials, but I also see the cotton plants have visually benefited from the treatment.
Should I increase my rate of insecticide or change to a different insecticide to improve control of thrips. The data suggests you will not see much improvement in control by increasing rates above normally recommended levels, and our recommended insecticides generally provide similar levels of control. Sorry, there are no magic options. There is one caveat. Radiant or higher rates of Acephate will perform better if you are dealing with western flower thrips, but every indication is that tobacco thrips are dominating this year.
Stick with standard rates if making a second application for thrips (Acephate at 0.20 – 0.25 lb, Bidrin at 2.5-3.0 oz, Dimethoate at 6 oz, or Radiant at 1.5 oz). You might lean more towards Radiant on a second application. It should save some beneficial insects, and might prevent future problems with spider mites. It will also clean up any western flower thrips that might be present (but it is more costly).
Consider that a second application is probably not needed. It is VERY hard to find data showing a yield response to a second foliar application when an at-planting treatment is used.
We are approaching the plant bug window on our earliest cotton, and I’ll hit on that topic next week, but the article linked below gives you a refresher about insecticide options and use strategies. ∆
http://news.utcrops.com/2016/05/insecticide-options-for-plant-bugs-in-cotton/
DR. SCOTT STEWART: IPM Extension Specialist, University of Tennessee
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