May Thrips Control in 2008
Roundup Ready Flex cotton varieties and glyphosate resistant weeds will likely change the way some growers approach weed control this coming year. There will be more use of preemergence and preplant incorporated materials to help deal with Roundup resistant weeds or to reduce the likelihood of developing resistant populations. Of particular concern here are horseweed and Palmer amaranth. Alternate chemistry is an important part of both controlling resistant weeds and reducing the likelihood of development of weed resistance. Alternate chemistry is considered to be more beneficial in resistance management when it is used early in the weed control period.
This will likely mean that over-the-top glyphosate applications may not be needed as early as they were in the total post systems many growers have used for the past few years. Often that early tank mix application of glyphosate plus insecticide to cotyledon to one-leaf cotton was perfect timing for thrips control, especially behind a seed treatment. If new weed control strategies - that include pre herbicides or Roundup Flex technology - delays the overtop application until later, growers will need to determine if separate foliar applications are needed for thrips control. This is especially likely on early cotton that grows off slowly and where seed treatments are used for thrips control.
Dr. Bacheler here at NCSU and Dr. Ames Herbert at Virginia Tech both have shown that thrips control is most crucial at the cotyledon to one-leaf stage. Because 5-leaf cotton is typically safe from thrips damage, delay in foliar applications for thrips to accommodate Roundup applications at the 3 or 4-leaf stage squanders most of the value of a thrips treatment, sometimes resulting in a serious yields loss or maturity delay.