title: Fate and efficacy of metolachlor granular and emulsifiable concentrate formulations in a conservation tillage system.
abstract: 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 glyphosate-resistant 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.
authors.affiliation: Southeast Watershed Research Laboratory, Agricultural Research Service, U.S. Department of Agriculture, PO Box 748, Tifton, Georgia 31793, USA. Tom.Potter@ars.usda.gov
authors.forename: Thomas L
authors.initials: TL
authors.lastname: Potter
authors.forename: Zev
authors.initials: Z
authors.lastname: Gerstl
authors.forename: Paul W
authors.initials: PW
authors.lastname: White
authors.forename: George S
authors.initials: GS
authors.lastname: Cutts
authors.forename: Theodore M
authors.initials: TM
authors.lastname: Webster
authors.forename: Clint C
authors.initials: CC
authors.lastname: Truman
authors.forename: Timothy C
authors.initials: TC
authors.lastname: Strickland
authors.forename: David D
authors.initials: DD
authors.lastname: Bosch
mesh_terms: D000081:Acetamides / Q000008:administration & dosage* / Q000032:analysis; D000383:Agriculture / Q000379:methods*; D000464:Alginates; D000538:Aluminum Silicates; D002837:Chromaffin Granules; D000077215:Clay; D004655:Emulsions; D020723:Glucuronic Acid; D003368:Gossypium / Q000254:growth & development; D006540:Herbicides / Q000008:administration & dosage* / Q000032:analysis; D006603:Hexuronic Acids; D012987:Soil / Q000032:analysis
chemical_list: D000081:Acetamides; D000464:Alginates; D000538:Aluminum Silicates; D004655:Emulsions; D006540:Herbicides; D006603:Hexuronic Acids; D012987:Soil; D020723:Glucuronic Acid; D000077215:Clay; C051786:metolachlor