Submitted to: Weed Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/8/2002
Publication Date: 7/1/2003
Citation: Teasdale, J.R., Shelton, D.R., Sadeghi, A.M., Isensee, A.R. 2003. Influence of hairy vetch residue on atrazine and metolachlor concentrations and weed emergence. Weed Science. 51:628-634. Interpretive Summary: Hairy vetch is a popular cover crop that is grown during the winter and spring months before planting corn in the mid-Atlantic states. Residue from a hairy vetch cover crop can provide many desirable benefits both to the succeeding corn crop and to the environment. High levels of this cover crop residue on the soil surface can suppress weed emergence, but it also can intercept herbicides that must be applied to soils and potentially will reduce their effectiveness. This research was conducted to compare the effect of residue from a hairy vetch cover crop to that of background crop residue present in no-tillage corn production on the widely-used, soil-applied herbicides atrazine and metolachlor. In a three-year field experiment, soil samples were taken to test for herbicide concentration and emerged weeds were counted at weekly intervals from plots with and without a hairy vetch cover crop and with and without herbicide. Results showed that high levels of hairy vetch residue reduced herbicide concentration in the soil to levels low enough to allow unacceptable numbers of weeds to emerge and grow. These results suggest that, in the presence of high levels of cover crop residue, weed control programs should eliminate herbicides that must be applied to soils for activity and use herbicides that are active when applied after emergence to weed foliage instead. These results will be useful to public and private scientists investigating the influence of plant residues on herbicides and to extension personnel who recommend appropriate herbicide programs to growers.
Technical Abstract: High levels of cover crop residue can suppress weed emergence, but also can intercept preemergence herbicides and potentially reduce their effectiveness. This research was conducted in continuous no-tillage corn plots to compare the effect of residue from a hairy vetch cover crop to that of background crop residue on the soil solution concentration of atrazine and metolachlor and on the emergence of weeds with and without herbicide treatment. In a three-year field experiment, soil samples and weed censuses were taken from paired microsites with and without herbicide at weekly intervals after application of atrazine and metolachlor until corn canopy closure. High levels of residue were present in both treatments; percent of soil covered by residue ranged from 90.9 to 98.9 in the no cover crop treatment and from 98.8 to 99.8 in the hairy vetch treatment. Metolachlor concentration was lower in the hairy vetch than the no cover crop treatment in all years, however, there was little or no difference in atrazine concentration between treatments. Annual grass weeds (predominantly fall panicum) were the major species in this field. Compared to the no cover crop treatment without herbicide, hairy vetch alone reduced grass emergence by an average of 74%, preemergence herbicides alone reduced emergence by 77%, and preemergence herbicides with hairy vetch reduced emergence an additional 13% over that achieved by vetch alone. Herbicide concentrations were low enough in all treatments that weed numbers exceeded threshold levels in all years. These results suggest that, in the presence of high residue levels with or without a cover crop, surface residue and/or preemergence atrazine and metolachlor do not control weeds sufficiently to provide full-season weed control.