In a survey conducted in 2003 producers were increasing the use of tillage to control GR horseweed. Tillage on many of the highly erodable soils of Tennessee is not a long term sustainable cotton production system. Research conducted at UT and elsewhere has identified several GR horseweed burndown systems that are very effective controlling this weed prior to planting without the use of tillage. Many growers were gaining confidence in and readily adapting to these new horseweed management systems. Unfortunately this last spring, many cotton producers in Tennessee did not obtain good control of GR horseweed prior to cotton planting using these systems. Many producers spent $20 dollars/A or more trying to burndown this one weed. Environmental conditions in early April appear to be the main culprit for the inconsistent horseweed control.

In the last 12 months two populations of Palmer amaranth (pigweed) in Tennessee have survived properly applied applications of full label rates of glyphosate. The Palmer pigweed at these locations in Tennessee has shown 2x more tolerance to glyphosate than a typical population. Currently we are working with growers who have confirmed glyphosate tolerant Palmer populations to help them manage and contain these glyphosate resistant biotypes in Tennessee. A major concern is that these two Palmer populations are not the only ones and that others may exist in the state. Therefore we have examined random Palmer pigweed populations in cotton for their overall sensitivity level to glyphosate. Results from this research will be presented.