Exploring a New Option for Thrips Suppression
January 2, 2022 You could almost feel the anticipation rising this past season about the commercial availability of Bayer’s new ThryvOn insect trait for 2022. Multiple years of university studies and on-farm trials by Bayer and by growers showed a positive impact on reducing plant bug treatments, as well as significant suppression of thrips.
But, at press time, regulatory issues have effectively delayed market introduction of new cotton varieties containing ThryvOn for another season. And with continuing concern about the dwindling impact of long-time seed treatments on thrips in early season cotton, growers will likely need to rely on a continued combination of seed treatments and foliar applications to keep the pests in check.
“We’re starting to look at possible resistance to acephate,” said Dr. Scott Stewart, Extension entomologist for the University of Tennessee, during the university’s annual Cotton Field Day. “We’re starting to see more injury in thinner plant populations, so we have to be more aggressive in thin stands.”
A study conducted by the University of Tennessee during the 2020 growing season looked at the efficacy of various foliar insecticides – including acephate – on thrips in seedling cotton. Conducted at the university’s Research and Education Center in Milan, TN, the study was set under poor seedling emergence conditions and severe thrip pressure, primarily tobacco thrips. Seven treatment options were compared, with first application at the one true leaf stage followed by a second application six days later when populations exceeded five thrips per plant with obvious signs of injury on emerging leaves.
When all was said and done, plots treated with Radiant or Intrepid Edge showed the least amount of thrips injury and the highest seed cotton turnout – 1,590 lbs/A for Intrepid Edge and 1,484 lbs/A for Radiant.
“Right now, those are my go-to recommendations,” noted Stewart.
Intrepid Edge is a premix of Intrepid 2F plus Radiant that was labeled primarily for lepidopteran control in soybeans. As the study showed, it also has efficacy on thrips in cotton.
“This research focuses on thrips suppression,” said Drew Ellis, Field Scientist with Corteva Agriscience. “I don’t know of any product currently on the market that truly controls this pest per se. Thrips injure young cotton plants, causing malformed growth and stunting and can be a vector for diseases. It really sets young cotton back and delays growth and ultimately impacts yield.”
Ellis noted that Intrepid Edge is approved for thrips suppression on a regional basis across the Cotton Belt through a 2ee supplemental label to the product’s full Section 3 label. The product is very effective in controlling tobacco thrips, but also provides protection against Western flower thrips.
“When you look at the thrips label for Intrepid Edge, use of an insecticide seed treatment is a requirement,” he explained. “Growers should scout their fields thoroughly and regularly for adults migrating in the field. The presence of adults is a good precursor for nymphs, which is when treatment needs to begin. This could be from first leaf emergence, past the cotyledon stage to the fourth or fifth leaf stage, which is generally a good cutoff point.”
Multiple applications per season of Intrepid Edge at 3 oz/A are permitted under the supplemental label. Corteva also recommends adding a surfactant to the product to help uptake into the plant.
In general, growers may try to rotate chemistries for severe thrips pressure. The most commonly used product for rotations is, of course, acephate.
“As the study shows, relying on acephate creates selection pressure for populations of tobacco thrips to become less sensitive – not necessarily resistant, but showing signs of slippage or inconsistency in control,” said Ellis. “Intrepid Edge is a better, more favorable rotation partner because it will also protect beneficials that will help control other pests like aphids after the thrips are gone.”
Another benefit: most early season foliar insecticide applications correspond with herbicide applications for early season weed control. In combination with most herbicides containing a surfactant, no additional surfactant for Intrepid Edge is needed.
“When you combine acephate with a herbicide, it increases the potential for crop injury or ‘burning’ that you wouldn’t get from either product individually,” pointed out Ellis. “Intrepid Edge provides a level of safety to help negate, but not repair, any potential injury that might happen.”
Feedback from growers who have tried the treatment rotation with Intrepid Edge have been pleased with the results. According to Ellis, scouts reported significant reduction in thrips population, in addition to general crop health benefits by allowing unaffected growth to the 5-leaf cutoff stages as quickly as possible without significant damage.
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