Potter, T.L., Southeast Watershed Research Laboratory, Tifton, GA 31793, United States
Gerstl, Z., Agricultural Research Organization, P.O. Box 6, Bet Dagan 50250, Israel
White, P.W., Southeast Watershed Research Laboratory, Tifton, GA 31793, United States
Cutts, G.S., Crop and Soil Science, University of Georgia, Athens, GA 30602, Greece
Webster, T.M., Crop Protection and Management Research Unit, Agricultural Research Service, U.S. Department of Agriculture, P.O. Box 748, Tifton, GA 31793, United States
Truman, C.C., Southeast Watershed Research Laboratory, Tifton, GA 31793, United States
Strickland, T.C., Southeast Watershed Research Laboratory, Tifton, GA 31793, United States
Bosch, D.D., Southeast Watershed Research Laboratory, Tifton, GA 31793, United States

Use of genetically modified cultivars resistant to the herbicide glyphosate (N-phosphonomethylglycine) is strongly associated with conservation-tillage (CsT) management for maize (Zea mays L.), soybean (Glycine max L.), and cotton (Gossypium hirsutum L.) cultivation. Due to the emergence of glyphosateresistant weed biotypes, alternate weed management practices are needed to sustain CsT use. This work focused on metolachlor use (2-chloro-N-(2-ethyl-6-methylphenyl)- N-(2-methoxy-1-methylethyl)acetamide) in a CsT system. The fate and efficacy of granular and emulsifiable concentrate (EC) formulations or an EC surrogate were compared for CsT cotton production in the Atlantic Coastal Plain region of southern Georgia (USA). The granular formulation, a clay-alginate polymer, was produced in the authors' laboratory; EC was a commercial product. In field and laboratory dissipations the granular metolachlor exhibited 8-fold greater soil persistence. Rainfall simulation runoff assessments indicated that use of the granular formulation in a common CsT system, strip-tillage (ST), may reduce metolachlor runoff loss when compared to conventional tillage (CT) management or when EC formulations are used in the ST system. Metolachlor leaching assessments using field-deployed lysimeters showed some tillage (ST >CT) and formulation (EC > granular) differences. Overall leaching was generally small when compared to runoff loss. Finally, greenhouse bioassays showed control of two weed species with the granular was greater than or equal to that of the EC formulation; however, the granular formulation suppressed cotton growth to a greater extent. In sum, this metolachlor granular formulation has advantages for CsT cotton production; however, additional research is needed to assess impacts on crop injury. © 2010 American Chemical Society.