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.
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