When Scott Stewart first saw an example of reduced control of thrips by one of the commercial seed treatments in cotton in 2011, he wrote it off to misapplication or failure to treat all of the seed in one field in west Tennessee.

“Most years we see very little difference in thrips control or cotton yields between the seed treatments,” said Stewart, professor and IPM coordinator with the University of Tennessee, speaking at the Southern Crop Consultants Meeting in Memphis, Tenn. “Sometimes we’ve seen higher yields with the seed treatments than with Temik in-furrow.”

When a similar problem occurred at the University of Tennessee’s Milan Experiment Station the following year, Stewart contacted the station’s resident director to try to determine the cause of the yield. It turned out researchers had applied high rates of Cotoran and Dual herbicides pre-emergence to combat glyphosate-resistant Palmer amaranth or pigweed in the plots.

“We know that pre-emergence herbicides can have an impact on seedling vigor and delay the crop,” said Stewart. “We thought the herbicides might also be preventing absorption of the thiamethoxam, the active ingredient in one of the seed treatments.”

But laboratory analyses showed the plants in the plots that received higher rates of pre-emergence herbicides also had higher levels of thiamethoxam.

Stewart and other Mid-South Extension entomologists assigned graduate students to study the problem in 2013. Results from their trials showed one of the two major active ingredients in seed treatments continued to provide better results than the other material.

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Members of the Mid-South Entomologists Working Group, which consists of Extension and university specialists from each of the major land-grant universities, are continuing to try to address the issue and will conduct further studies, according to Stewart.

Although the entomologists were able to apply Temik for comparison purposes in their trials, Temik is no longer on the market, despite the efforts of one or two companies to try to bring a Temik or Temik-like compound to market.