Metolachlor, S-metolachlor and their role within sustainable weed-management

• Published in: Crop protection 1998-05, Vol.17 (3), p.207-212
• Main Authors: O'Connell, Peter J., Harms, Christian T., Allen, James R.F.
• Format: Article
• Language: English
• Subjects: crop tolerance; grassy weeds; half life; maize; residual activity; S-metolachlor
• ISSN: 0261-2194; 1873-6904
• DOI: 10.1016/S0261-2194(98)80011-2

The herbicide metolachlor has been widely used for over 20 years for selective weed control in more than 70 crops worldwide. Its favourable soil behaviour and low risk for developing weed resistance means that metolachlor integrates well into sustainable weed-management practices, such as conservation tillage. Metolachlor consists of four stereoisomers, with herbicidal activity coming mainly from the S-isomer pair. A new catalyst system developed allows the commercial production of enantiomerically-enriched S-metolachlor (ISO draft common name). In field trials carried out 1995–1996 S-metolachlor demonstrated equivalent efficacy on major grass weeds and tolerance to different maize cultivars at 65% the use rate of metolachlor. In laboratory studies in different soils degradation half-lives were similar for metolachlor and S-metolachlor. The mean half life of S-metolachlor was 23 days in dissipation studies at different European field sites. At the lower use rates and with highly concentrated formulations containing up to 96% (w/v) active ingredient, the use of S-metolachlor will result in a substantial reduction of risk to applicators, consumers and the environment and the herbicide will continue to play an important role in sustainable weed-management.