Lolium multiflorum Lam. (annual ryegrass) is a problematic weed species especially in no-tillage systems of the southern region of Buenos Aires province (Argentina). Increasing herbicide resistance cases have exacerbated the problem, requiring alternative control options based on an Integrated Weed Management approach (IWM). Field experiments were conducted in the south area of Buenos Aires province during 2017-2019 in order to evaluate both the suppressive effect of Vicia villosa (hairy vetch) over annual ryegrass when combined with residual herbicides, and the tolerance of the former to such herbicides. Annual ryegrass stand density and biomass at crop termination were reduced from 2 – 98% in response to combined hairy vetch plus herbicide treatments. Among the best chemical options, pyroxasulfone, acetochlor and S-metolachlor should be mentioned, reaching weed biomass control values of 97, 81 and 76%, respectively. Hairy vetch was partially affected by herbicides with a plant stand reduction ≤ 48%. No significant effect on biomass at crop termination was observed, except for diflufenican and trifluralin. The inclusion of hairy vetch as cover crop combined with residual herbicides could be a practical IWM practice for suppression of annual ryegrass populations resistant to ACCase, ALS and EPSPS inhibitors.

Keywords: cover crops, weed management, legumes, chemical control.