We are definitely having a tough thrips year in cotton, somewhat less in peanut. Growers have reported less control than normal with treatments of Orthene/Acephate, even at rates that used to provide good control. Two things may be happening. One is that treatments did kill a lot of thrips but fields are being continually invaded by adults, especially from nearby grain fields that are drying down. Or, earlier treatments killed most of the tobacco thrips and left or ‘encouraged’ outbreaks of western flower thrips that are much less susceptible to Orthene/Acephate. The only way to confirm a western thrips population is to provide our lab with a soapy/jar sample of clipped seedlings. We rinse them from the plants and ID them using a microscope. Without the knowledge of what species are present, it becomes a question of what insecticide to use. We are rating trips trials daily to generate the data to help guide that decision. For example, in one test we made two foliar applications, the first at bud stage and the second in 7 days. As of this week, we had an average of 71 thrips larvae in the 5-plant sample from the untreated control (definitely a lot of pressure). Orthene 97 at 4 oz provided 87% control, Radiant at 6 oz provided 78% control, Vydate C-LV at 17 oz 77% control, Lannate 2.4LV at 12 oz 67% control, and Karate Z at 1.28 oz 8% control. There were two surprises. Dimethoate 4EC at 8 oz provided 95% control, but this is higher than we have ever seen previously with this product and it may be a ‘misread’. And, the new product Benevia 10OD (Cyazypyr) by Dupont, which is not labeled yet, provided 98% control.
Here are a few thoughts based on these data and what we are seeing in fields. First, cotton in many fields is close to being in the 4-5 true leaf stage, on the other side of the thrips pressure period when no further thrips treatments are needed. With the recent rains and warm-hot weather, we will see a lot of growth in the next week. Second, there does not seem to be a ‘silver bullet’ product for thrips control as some may lead you to believe. Orthene/Acephate is still hard to beat, with the exception of this new Benevia which is not labeled, yet. But there is a risk to multiple applications of Orthene. It is tough on beneficial insects and could lead to a much higher risk to flaring mites and aphids….remember that Temik was providing early season suppression of both of these pests. If a second spray is being considered (still seeing damage to the new bud), it might make good sense cost-wise to shift to Dimethoate at 8 oz, which seems to work pretty well and can provide some control of spider mites (is used by soybean growers for spider mite control in DE and MD). The cotton entomologist at Univ of Georgia also recommends Bidrin at 3.2 oz. I have not tested Bidrin, but trust his knowledge.
We will continue to monitor thrips and our many research trials and look forward to sharing our result at our upcoming field tour on June 2.