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With the evolution of glyphosate-resistant weeds, cotton producers now rely on multiple applications of soil-residual herbicides tank-mixed with postemergence (POST) herbicides. However, the current soil-residual herbicides represent a relatively low number of herbicide mechanisms of action (MOAs), with the same few MOAs being utilized year after year. Therefore, it is important to introduce new MOAs to slow the likelihood of further resistance development. A field experiment was conducted in 2012 and 2013 to determine if fluridone, a bleaching herbicide currently not used in any agronomic cropping system, applied preemergence (PRE) would provide effective season-long control of Palmer amaranth as well as reduce the number of POST applications throughout the season. Fluridone PRE at 224, 336, and 448 g ai ha-1 did not eliminate the need for POST herbicides for Palmer amaranth control in cotton in either year. Fluridone, regardless of rate, provided comparable control to fluometuron in 2012; however in 2013, fluometuron provided less control than fluridone. Although moderate season-long control was observed in 2013, greater seed cotton yields were obtained in 2013 than in 2012, which is likely a result of greater control during the critical period for weed control. Based on this experiment, fluridone will not provide effective season-long Palmer amaranth control in the absence of a multiple POST-herbicide program.

The herbicide fluridone is a soil-residual herbicide that should provide effective control of several problematic agronomic weeds, but because of herbicide persistence, injury to rotational crops is possible. In this experiment, multiple rates of fluridone were applied PRE to cotton at four irrigated locations across Arkansas to determine the risk of fluridone persisting and injuring subsequently planted wheat, corn, soybean, rice, grain sorghum, and sunflower. The multiple rates of fluridone were compared with fluometuron and evaluated for percentage of crop injury, crop density, and potential yield loss for each crop at the end of the subsequent growing season. Regardless of the location, wheat exhibited the greatest injury with 13 to 26% at Fayetteville (silt loam), 8 to 15% at Pine Tree (silt loam), 2 to 7% at Keiser (silty clay), and 3 to 8% at Rohwer (silty clay). Along with high levels of injury to wheat, fluridone at 900 g ai ha−1caused loss of wheat stands to 29 plants m−1row compared with fluometuron, which had stands of 49 plants m−1row. Although injury occurred in wheat at all locations, no rate of fluridone reduced wheat yields compared with fluometuron. Injury to grain sorghum ranged from 5 to 10% from all rates of fluridone at Pine Tree. Fluridone at 900 g ha−1(11 plants m−1row) also reduced grain sorghum stands at Pine Tree over that of fluometuron (19 plants m−1row). A decrease in grain sorghum yield was also observed from fluridone at 448, 673, and 900 g ha−1compared with fluometuron at Pine Tree. At Keiser, rice exhibited significant levels of injury (1 to 13%) from fluridone 393 d after treatment. In conclusion, injury to a wheat rotational crop is more likely following an application of fluridone in cotton than is injury to other rotational crops, but yield reductions are not expected for most rotational crops when fluridone is applied to cotton at an anticipated labeled rate of 224 g ha−1.

Glyphosate-resistant Palmer amaranth is considered the most troublesome weed in agronomic crops in the Midsouth. The reliance on multiple herbicide mechanisms of action (MOA) and soil-residual herbicides has increased over the past several years due to the ever growing issue of herbicide-resistant weeds. Field experiments were conducted at several locations in Arkansas to determine the efficacy of fluridone on Palmer amaranth in glyphosate-resistant and glufosinate-resistant cotton herbicide programs and to determine the length of residual fluridone activity when applied preemergence (PRE). Fluridone has a unique MOA and is currently not registered as a stand-alone herbicide for use in cotton. In the length of residual experiment, when rainfall was adequate, fluridone applied PRE at rates greater than 224 g a.i. ha-1 provided > 90% Palmer amaranth control for 6 wk after application; however, effective season-long Palmer amaranth control was not achieved with any rate of fluridone alone. Fluridone alone applied 14-d preplant or PRE did not provide greater Palmer amaranth control than a standard herbicide application. When fluridone was integrated into a glufosinate-based herbicide program, PRE-applied fluridone at 224, 336, and 448 g ha-1 did not provide greater Palmer amaranth control than the standard herbicide program that included fluometuron. Based on these experiments, fluridone should not be applied as a stand-alone herbicide in cotton, nor will it reduce the number of POST applications needed for effective Palmer amaranth control in glufosinate-resistant cotton.