– Kurt M. Vollmer, Postdoctoral Researcher, University of Delaware; email@example.com
There are often comments from growers who have switched from using s-metolachor containing products (Dual, Cinch, Bicep) to ones containing acetochlor (Breakfree, Degree, Harness, Keystone, Surpass, and Warrant). However, this switch may not necessarily provide better weed control; rather control of different weeds that may have not been as prevalent when s-metolachor was being used. Both of these are Group 15 herbicides and are generally effective on grasses and small-seeded broadleaf weeds, but there are some differences in the control of certain weed species. Acetochlor provides slightly better control of pigweeds and better suppression of lambsquarters and common ragweed. It also has activity on smartweed and velvetleaf, compared to no control with s-metolachor. Both herbicides provide similar levels of control on grass species including: barnyardgrass, bermudagrass, crabgrass, fall panicum, foxtail, goosegrass, and quackgrass. S-metolachor also tends to have longer soil residual activity than acetochlor.
An activating rainfall is required for both of these herbicides, but s-metolachor requires less moisture to activate than acetochlor. The addition of atrazine to the tank mix of either herbicide will provide more effective preemergence control than either acetochlor or s-metolachlor alone, including control of morningglory and pigweed species.