Pyroxsulam is a new wheat residual herbicide available for use under the trade name Powerflex®. It will be important component for herbicide resistant weed control in Georgia wheat. Many farmers double crop wheat with either soybean or cotton. However, little information about pyroxsulam residual activity to these rotational crops is available. Therefore, studies were conducted in 2007-2008, and continuing in 2008-2009, for applications of pyroxsulam to autumn and winter treated wheat followed by rotational crops of soybean and cotton. Two studies were conducted that evaluated the effects of pyroxsulam applied at 90 or 180 days before planting rotational crops. Pyroxsulam was applied at 18.5, 37, or 73.5 g ai/ha. Other herbicides included mesosulfuron at 150 and 300 g ai/ha, propoxycarbazon at 44 and 88 g ai/ha, and sulfosulfuron at 35.2 and 70.4 g ai/ha. Studies were conducted in Georgia at Tifton on a Tift loamy sand soil and Plains on a Greenville sandy loam soil. Wheat was evaluated for injury and yield. Soybean and cotton were evaluated for injury, stand establishment, and height.
For both locations and timings of herbicide application, wheat tolerance to proxysulam was excellent, with little to no visual injury 7 to 90 days after application (DAP). In contrast, propoxycarbazone injured wheat 0 to 33%. Sulfosulfuron and mesosulfuron injury was similar to proxysulam. Wheat injury was transient and there was little to no observed pyroxsulam effect, there was a trend for lower yields with the propoxycarbazone treatment.
Soybean was planted at both locations. For both locations and timings of herbicide application there was little difference in the stand counts for most herbicide treatments. There was a trend for slight soybean stand reduction at the Plains location for sulfosulfuron. There were no height differences for soybean between herbicides in both locations and herbicide timings. There was little to no soybean herbicide injury, except with the sulfosulfuron at Plains for the 90 day treatment. Sulfosulfuron injury was rated 57 and 52% at 147 and 154 DAP, respectively.
Cotton was only planted at Plains. There was no effect of herbicide treatment on cotton stand. There was no herbicide effect on cotton height for the 180 day treatment, for the 90 day treatment sulfosulfuron caused a slight stunting. For the 90 day treatment there was noticeable herbicide injury by sulfosulfuron to the cotton. Sulfosulfuron injury was rated 56 and 25% at 147 and 154 DAP, respectively.
In most treatments, injury was transient and occurred early in growth of the plants. For the two studies evaluated, there was little to no difference in residual activity on soybean and cotton rotational crops between the pyroxsulam and other herbicides labeled for use in wheat.