It’s hard to stay on top of things with replanting, planting, fertilizing, herbicide applications and preparing for wheat harvest. Thrips in cotton are the primary pest concern at this time, but it won’t be long until our earliest cotton begins to square. It will then be plant bug time. I will talk more on plant bugs in the coming weeks. Until then, be alert on the earliest planted fields because they often act as a trap crop for plant bugs.
Thrips populations are at extremely high levels in many fields, and I received the following questions.
1) What about Radiant? Radiant is a good product for thrips control and will shine if western flower thrips are the primary species. Please follow label instructions on using an adjuvant. It matters with this product. Typical use rates are 1.5 oz/acre, but it will cost more. However, if you are dealing with are typical thrips species, my data suggests it it is not better than the alternatives. On the upside, it is probably less likely to flare secondary pest outbreaks and mixes well with herbicides. I discussed Radiant and other options in a previous article (link here). My data suggests that when dealing with high numbers of thrips, it takes 2 applications at a 4-5 day interval to really knock populations down, regardless of the product. This doesn’t mean you typically need two insecticide applications. Usually, a few days of reprieve from a single application does a lot of good. Reserve two applications for cases where at-planting treatments are failing soon after emergence. Making applications to 4th or 5th leaf cotton is seldom justified.
2) Should I make a third spray for thrips? I know this is a related question. The answer is almost never pays to make a third application for thrips control. I would have to look very hard to find an example where it did. And heck, who has time this year? The possible exception might be extreme pressure and where at-planting treatments are completely failing. Your first instinct should be no!
3) Will I see burn if I include acephate (e.g., Orthene) with applications of glyphosate, Liberty or Dual? I’ve done a lot of work on this, much of it in cooperation with Larry Steckel. In these wet and humid conditions, the short answer is yes, but it is almost always the herbicide to blame. In many tests, I’ve never seen an example where acephate adds appreciably to herbicide injury. I have observed more injury with Bidrin and Dimethoate (but almost always tolerable). Even glyphosate may cause some minor burn under the right conditions. This week, I smoked some Phytogen 375 WRF cotton with an application or Liberty (even worse if Dual was included). Dual by itself caused “acceptable” levels of injury, and glyphosate caused some but very minor injury. No insecticide was needed for this result. Never say never, but I’m more concerned about the injury that thrips may cause than any added injury from acephate that is tank mixed with herbicides. In my opinion, and based on some pretty good data, Acephate and Radiant are probably the safest thrips products to tank mix with herbicides. I suggest avoiding the EC formulations such as Bidrin or Dimethoate if co-applying Liberty to non-Liberty Link cotton or Dual or Sequence to any variety. Keep in mind the pyrethroid insecticides typically provide POOR control of thrips.
