SYNERGISM BETWEEN COVER CROP RESIDUE AND HERBICIDE ACTIVITY ON EMERGENCE AND EARLY GROWTH OF WEEDS

Authors: Teasdale, John; Pillai, P; Collins, Ronald

Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/12/2005
Publication Date: 7/1/2005
Citation: Teasdale, J.R., Pillai, P., Collins, R.T. 2005. Synergism between cover crop residue and herbicide activity on emergence and early growth of weeds. Weed Science. 53:521-527.

Interpretive Summary: During the past decade, researchers and farmers have been developing preventive systems for controlling weeds that minimize the use of interventions such as herbicides. Many biologically based weed management approaches have been explored but most have limited efficacy and are inconsistent. Cover crops are an important tool for protecting soil, managing nutrients, and suppressing pests in sustainable production systems. Cover crop residue left on the surface of soil can suppress weeds but this effect is incomplete and inconsistent. This research explored the mathematical relationships between the amount of residue of the cover crop, hairy vetch, and the amount of the herbicide, metolachlor, applied to the soil surface. A synergistic relationship was demonstrated, meaning that by combining amounts of residue and herbicide that are marginally effective when used alone, a high degree of weed control was achieved. These results could open a new area of research that would target combinations of cover crops and low levels of selected phytotoxins to maximize weed control with minimal environmental impact. Immediate users will be researchers but ultimate beneficiaries will be growers and consumers.

Technical Abstract: Weed control by cover crop residue and other ecologically based approaches is often incomplete and inconsistent. This research was conducted to determine synergistic interactions between hairy vetch residue on the surface of soil and the herbicide, metolachlor. Residue and herbicide rates as well as potentially confounding variables were controlled in a greenhouse experiment. Deviation from a multiplicative model that included a linear quadratic response to 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 was reduced synergistically by the combination of vetch residue and metolachlor. This model could be used to determine synergistic interactions between any combination of a biologically based approach that can be expressed in quantitative units and a phytotoxin. The targeted development of synergistic interactions between agents that alone are only effective as 'little hammers' should be a priority for development of effective biologically based weed management systems.