Mechanical versus herbicidal strategies for killing a hairy vetch cover crop and controlling weeds in minimum-tillage corn production

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Abstract
The development of production systems that provide the benefits of reduced tillage and also reduce or eliminate herbicide inputs presents a challenge to practitioners of sustainable agriculture. This research was conducted to evaluate management approaches for minimum-tillage corn production in a hairy vetch cover crop, specifically, mechanical versus herbicidal methods for pre-plant cover-crop kill and for post-emergence control of emerged weeds. Pre-plant treatments included 2,4-D [(2,4-dichlorophenoxy)acetic acid] plus residual herbicides, 2,4-D alone, flail mower, corn stalk chopper, light disk and heavy disk. The pre-plant herbicide treatments were followed by a post-emergence treatment of dicamba, whereas the pre-plant mechanical treatments were followed by post-emergence cultivation, as needed, for weed control. The mechanical treatments that kept residue on the soil surface (mower, stalk chopper and light disk) killed hairy vetch when it was flowering, but not when vegetative. The herbicide treatment with pre-plant 2,4-D alone, followed by dicamba post-emergence, controlled annual broadleaf weeds (the dominant species in these experiments) similarly to treatment with 2,4-D plus residual herbicides, suggesting that residual herbicides may be eliminated in cover-crop-based no-tillage systems. The pre-plant mechanical treatments followed by cultivation did not control annual broadleaf weeds as well as herbicide treatments, but did maintain final populations below threshold levels in two of four experiments. The stalk chopper and light disk left high levels of vetch residue on the soil surface, and reduced initial broadleaf weed populations compared with the heavy disk that incorporated residue. However, broadleaf weed populations were reduced with less efficiency by cultivation of unfilled soil following the stalk chopper or light disk (38–69%) than by cultivation of tilled soil following the heavy disk (87–95%). Thus, although maintaining surface cover-crop residue without tillage initially reduced weed emergence, it also reduced the efficiency of cultivation, leading to similar final weed populations in all mechanical-based, pre-plant treatments.