|Gerstl, Zev -|
|Cutts, George -|
Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 28, 2010
Publication Date: October 1, 2010
Citation: Potter, T.L., Gerstl, Z., White Jr, P.M., Truman, C.C., Cutts, G.S., Webster, T.M., Strickland, T.C., Bosch, D.D. 2010. Fate and efficacy of metolachlor granular and emulsifiable concentrate formulations in a conservation-tillage system. Journal of Agricultural and Food Chemistry. 58(19):10590-10596. Interpretive Summary: The herbicide, metolachlor, provides effective control of many problematic weeds including those resistant to the widely used product, glyphosate; however, as with the case with many herbicides there appears to be some reduction in efficacy when products containing metolachlor are used in conservation-tillage (CsT) systems. Use of alternative formulation technology offers potential as a cost effective solution. We compared the fate and efficacy of a granular alginate-encapsulated product prepared in our laboratory to a standard commerical formulation. Comparisions were made on the basis of tillage, CsT, and conventional, i.e no surface crop residue at planting (CT). Strip-tillage (ST), a commonly used form of CsT, was practiced. The soil dissipation rate for metolachlor when applied in the commercial formulation was 8 times faster than when the alginate was used. The longer soil residence time inferred for metolachlor in the alginate formulation suggests that it use may enhance weed management in cotton and peanut fields in the region. Comparison of alginate and commercial formulations in rainfall simulations and leaching studies also showed that ST may effectively reduce runoff and leaching impacts. Addtionally, similar weed control efficacy was indicated in greenhouse evaluations, although studies indicated that the granular product has increased potentil for crop-injry. Study findings have indicated that use of granular herbicide formulations like the alginate used in this study may have substantial benefit for ST-system weed management for cotton and peanut production under Atlantic Coastal Plain conditions in the southeastern USA. Commercial development and evaluation at the farm scale appears warranted. Products will likely enhance and maintain CsT use in this and other regions by improving weed control options.
Technical Abstract: Use of genetically modified cultivars resistant to the herbicide glyphosate (N-phosphonomethyl-glycine) is strongly associated with conservation-tillage (CsT) adoption for maize (Zea mays L.), soybean (Glycine max L.), and cotton (Gossypium hirsutum L.) cultivation. Due to emergence of glyphosate-resistant weed biotypes alternate weed management practices are needed to sustain CsT use. This work focused on use of metolachlor (2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)-acetamide) in CsT systems. 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 GA (USA). The granular formulation, a clay-alginate polymer, was produced in our laboratory; the 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 CT management or when EC formulations are used in ST-systems. Metolachlor leaching assessments using field deployed lysimeters did not show a strong impact of tillage or formulation on the mass loss in leachate and leaching was generally small when compared to runoff loss. Finally greenhouse bioassays showed control of two weed species with the granular formulation was greater or equal to 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.