ARS | Publication request: Tillage, cover-crop residue management, and irrigation incorporation impact on fomesafen runoff

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 21, 2011
Publication Date: June 21, 2011
Citation: Potter, T.L., Truman, C.C., Webster, T.M., Bosch, D.D., Strickland, T.C. 2011. Tillage, cover-crop residue management, and irrigation incorporation impact on fomesafen runoff. Journal of Agricultural and Food Chemistry. 59:7910-7915.

Interpretive Summary: Commercial cropping systems worldwide depend on herbicides for weed control. One of the most highly valued active ingredients in these products is glyphosate. It is the world’s most widely used herbicide and accounts for more than 1/3 of all pesticides used on farms in the USA. The product is highly effective and has been successively integrated into cotton, soybean and corn production systems though biotechnology. Glyphosate is also relatively non toxic, breaks down in the environment quickly, and adsorbs to soil strongly; thus risks to human health and the environment from glyphosate use appear small. A direct consequence of the intense use of this product is evolution of glyphosate-resistant populations of several economically damaging weed species. To sustain glyphosate use and reduce losses growers are advised to rotate and or substitute other herbicides. Some of the most promising for cotton growers in the Southeastern USA are products that contain the active ingredient fomesafen. This active ingredient effectively controls some of the region’s most troublesome weeds. While effective, concerns persist about the potential for fomesafen to be carried into rivers and streams with stormwater runoff from treated fields. We conducted studies to evaluate two mitigation strategies, incorporation with irrigation after herbicide application and use of conservation-tillage. Both practices were found to reduce fomesafen runoff potential by more than 2-fold. Results indicate that these practices should be implemented wherever possible to reduce fomesafen runoff risk.

Technical Abstract: Intensive glyphosate use has resulted in emergence of resistant weeds that threaten production of many crops. Sustained use of this highly valued herbicide requires rotation and or substitution of herbicides with different modes of action. Cotton growers have shown considerable interest in the protoporphyrinogen oxidase inhibitor, fomesafen. Following registration for cotton in 2008, use has increased rapidly. Environmental fate data in major use areas are needed to appropriately evaluate risks. Field-based rainfall simulation was used to evaluate fomesafen runoff potential without irrigation incorporation in a conventional-tillage system (CT) and behavior when conservation-tillage (CsT) was practiced. Relatively high runoff, about 5 % of applied, was measured from the CT-system indicating that compound may present a runoff risk. Runoff was reduced more than 50% when the herbicide was irrigation incorporated after application or when used with a CsT system. Data indicate that these practices should be implemented wherever possible to reduce fomesafen runoff risk. Results also raised concerns about leaching and potential groundwater contamination and crop injury due to rapid washoff from cover crop residues in CsT systems. Further work is needed to address these concerns.