Submitted to: Weed Science Society of America Meeting Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: September 29, 2005
Publication Date: February 13, 2006
Citation: Teasdale, J.R., Pillai, P., Collins, R.T. 2006. Synergism between hairy vetch residue and low rates of metolachlor [abstract]. Weed Science Society of America Meeting Abstracts. 46:51.
Cover crop residues and other biologically based approaches often provide incomplete and inconsistent weed control. Consequently, biologically based weed management will necessarily require combinations of tactics to develop effective weed control strategies. Strategies that can target potential synergistic interactions will be needed to attain high levels of weed control if each component tactic is less than effective by itself. This research was conducted to evaluate interactions between hairy vetch residue on the surface of soil and the herbicide metolachlor. Metolachlor was applied and incorporated with simulated rainfall before residue placement, residue was applied to the soil surface at precise rates, and potentially confounding variables such as nitrogen and soil moisture were controlled in a greenhouse experiment. Emphasis was placed on using sub-optimal rates of both residue and metolachlor to explore the potential synergistic interactions between these factors. Deviation from a multiplicative model that included a quadratic response to hairy vetch residue and a log-logistic response to metolachlor was used to demonstrate the presence or absence of synergism. This model effectively showed that emergence of smooth pigweed, common lambsquarters, giant foxtail, and velvetleaf and early growth of smooth pigweed and common lambsquarters were reduced synergistically by the combination of hairy vetch residue and metolachlor. For example, smooth pigweed emergence was reduced 13% by 500 g m-2 of hairy vetch residue, alone, and was reduced 16% by 10 g ha-1 of metolachlor, alone, but together they reduced smooth pigweed emergence by 86%. This research suggests that the synergistic combination of cover crop residue plus low rates of phytotoxins requiring metabolic detoxification could provide an effective biologically based system.