I have had a couple of calls about thrips showing up on cotton. We counted a thrips test today and didn’t find many thrips – of course I was expecting that since it rained the day before. It is important to remember that rain can really knock back populations but if you missed the rain, thrips could be feeding happily on your young cotton.
South of us, there have been high thrips populations – so high that seed treatments aren’t able to hold them back. Part of that can be a result of species composition. For the past two years, we have looked at thrips on cotton in MO as part of our regional thrips project. Last year our composition was 55% tobacco thrips, 21% western flower thrips, 15% soybean thrips, 5% flower thrips and 4% onion thrips. Of these, western flower thrips are the most difficult to control.
Typically cotton past the 4th leaf is considered safe from thrips damage. You can sample for thrips by getting 5 plants and gently beating them in a white bucket or piece of paper and looking for little dashes that move. If you have a hand lens, you can get a better view. If you average around 2-5 per plant, a foliar application may be warranted
I have had a couple of calls about tank-mixing herbicide (Dual and similar products) with some of the insecticides labeled for thrips (acephate, bidrin and dimethoate). I called around to see what the likelihood for the injury would be for the tank mix. Everyone that I talked to said that since you will see injury with the herbicide alone, they would not support a tank mix because there is a chance that injury may be more severe.
It is also important to remember that foliar applications can flare mites, so make sure the application is needed before spraying unnecessarily. There is a new product that has a 2(ee) label, Radiant (Dow AgroSciences); it is related to the same chemical that is used in Tracer. Limited research has shown that the use of a non-ionic surfactant (0.25% v/v) can increase efficacy. Radiant is less likely to flare mites, however, it may be more expensive than the previously mentioned alternatives.