Author
 |
Potter, Thomas |
|
Submitted to: United States-Israel Binational Agricultural Research and Development Fund Workshop for Promoting Regional Cooperative Agricultural R&D in the Middle East
Publication Type: Other Publication Acceptance Date: 6/1/2009 Publication Date: 8/27/2009 Citation: Potter, T.L. 2009. Protection of Water Quality by Novel Herbicide Formulations. United States-Israel Binational Agricultural Research and Development Fund Workshop for Promoting Regional Cooperative Agricultural R&D in the Middle East. Interpretive Summary: Numerous studies have demonstrated that conservation-tillage (CsT) promotes environmental quality and enhances sustainable crop production. Continued increases and or current use of CsT-practices appears threatened unless cost effective alternative weed control practicies can be found. This is because of the heavy reliance by CsT practioners on the broad-spectrum herbicide, glyphosate, and recent discoveries of troublesome weeds that are highly resistant to products containing this active ingredient. The problem is pressing in the southern portion of the Atlantic Coastal Plain region of the eastern USA where cotton and peanut are producing extensively. This research addressed needs of the region’s farmer’s for more effective weed control practices for CsT systems. Over three years, field and laboratory investigations were conducted that focused on evaluting the environmental fate and weed control efficacy of a commercially available, and two controled release formulations of the soil-residual herbicide metolachlor. Metolachlor provides effective control of many problematic weeds including those resistant to glyphosate; however, as with the case with many herbicides there appears to be some reduction in efficacy when the products are used in CsT managed systems. Use of alternative formulation technology offers potential as a cost effective solution. We examined an organo-clay based and granular alginate-encapsulated products. The formulations were prepared under the guidance of Israeli colloborators on this project. The environmental fate characteristics and weed control efficacy of these products were compared to a commericial “generic” metolachlor formulation through conduct of rainfall simulations, soil dissipations, greenhouse efficacy trials on selected weed species, and a leaching study. 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. In comparisons, the organo-clay and commercial metolachlor formulations behaved similarly in terms of cover crop mulch washoff and in runoff response associated with irrigation incorporation. Metolachlor soil dissipation rates and weed control efficacy associated with application of these formulations was also nearly identical. Results did not indicate an advantage of the organo-clay over the commercial metolachlor products; thus, further development and use of the organo-clay based products for farming systems in the region are not recommended. The studies comparing the commercial generic product and alginate encapsulated metolachlor that was applied in granular form were more promising. Again similar weed control efficacy was indicated in greenhouse evaluations. However, the dissipation rate for metolachlor when applied in the commercial formulation was 10-fold faster than when the alginate was used. The much 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. In addition, comparison of alginate and commercial formulations in rainfall simulations showed that ST can effectively reduce the runoff threat that is commonly associated with granular herbicide application. A similar response was found in leaching studies. Use of the alginate in the ST-system reduced leaching potential. Overall study findings have indicated that use of granular herbicide formulations 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 enhances and maintain CsT use in this and other regions by improving weed control options. Technical Abstract: Over three years, field and laboratory investigations were conducted that focused on evaluting the environmental fate and weed control efficacy of a commercially available, and two controled release formulations of the soil-residual herbicide metolachlor. Metolachlor provides effective control of many problematic weeds including those resistant to glyphosate; however, as with the case with many herbicides there appears to be some reduction in efficacy when the products are used in CsT managed systems. Use of alternative formulation technology offers potential as a cost effective solution. In the current studies we examined an organo-clay based and granular alginate-encapsulated products. The formulations were prepared under the guidance of Israeli colloborators on this project. The environmental fate characteristics and weed control efficacy of these products were compared to a commericial “generic” metolachlor formulation through conduct of rainfall simulations, soil dissipations, greenhouse efficacy trials on selected weed species, and a leaching study. 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. In comparisons, the organo-clay and commercial metolachlor formulations behaved similarly in terms of cover crop mulch washoff and in runoff response associated with irrigation incorporation. Metolachlor soil dissipation rates and weed control efficacy associated with application of these formulations was also nearly identical. Results did not indicate an advantage of the organo-clay over the commercial metolachlor products; thus, further development and use of the organo-clay based products for farming systems in the region are not recommended. The studies comparing the commercial generic product and alginate encapsulated metolachlor that was applied in granular form were more promising. Again similar weed control efficacy was indicated in greenhouse evaluations. However, the dissipation rate for metolachlor when applied in the commercial formulation was 10 faster than when the alginate was used. The much 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. In addition, comparison of alginate and commercial formulations in rainfall simulations showed that ST can effectively reduce the runoff threat that is commonly associated with granular herbicide application. Metolachlor runoff from ST plots treated with either the commercial or alginate formulations was not significantly different and total loss was nearly three times less than when the alginate formulation was evaluated on CT plots. A similar response was found in leaching studies. Comparable amounts of metolachlor were leached in lysimeters containing CT and ST soil when both the alginate and commercial products were applied. The amount leached was less than observed when the commercial product was examined under ST conditions. This indicated that the alginate formulation has the potential to reduce metolachlor leaching. Further work is needed to confirm this. This is indicated since the commercial formulation had the lowest over leaching rate when CT soil was used in lysimeters. Overall study findings have indicated that use of granular herbicide formulations 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 enhances and maintain CsT use in this and other regions by improving weed control options. |
