Cover Crop Termination Treatment Impacts Weed Suppression Potential

Weed management in tobacco (Nicotiana tabacum L.) is accomplished primarily with soil-residual herbicides, cultivation, and hand removal. Management practices that reduce weed emergence, like reduced tillage and cover crop mulches, may improve weed management efficacy. Depending on cover-cropping goals, growers face trade-offs in species selection and management priorities-producing weed-suppressive mulches may lead to transplanting difficulties and soil-residual herbicide interception. Managing more complex cover crop mixtures may result in different challenges. We established on-farm trials across 4 site-years to study impacts of cover crop composition [wheat (Triticum aestivum L.) monoculture or mixture], termination treatment (early or late chemical termination or removing above-ground biomass), and soil-residual herbicides on weed density and biomass. The cover crop mixture contained cereal rye (Secale cereale L.), crimson clover (Trifolium incarnatum L.), and hairy vetch (Vicia villosa Roth.), with canola (Brassica napus L.) at 1 site-year. The mixture typically produced more biomass than monoculture wheat, although composition had few impacts on weed density or biomass. With residual herbicides, termination treatment had few impacts on weed density, suggesting that residues did not adversely affect herbicide efficacy. Without residual herbicides, early-season weed density was often higher following the late-terminated cover crop compared with other termination treatments, though midseason weed density was typically lower. When termination treatment affected final weed biomass, it was lower following late termination, with one exception-crop establishment was reduced at 1 site-year, leading to reduced weed-crop competition and greater weed biomass. Our results suggest that growers can use mixtures and, if well-timed to a rainfall event for incorporation, still effectively use soil-residual herbicides to maintain adequate weed control in tobacco regardless of how the cover crop is managed. Later termination, resulting in more residue, may lead to less weed biomass accumulation in the absence of herbicide use.