Under-vine cover crops in viticulture: impact of different weed management practices on weed suppression, yield and quality of grapevine cultivar Riesling (Vitis vinifera L.)

Sustainable viticulture increasingly depends on alternative floor management strategies to improve vineyard resilience to weather extremes, while supporting grapevine health and economic viability. One such strategy is the use of perennial and short-lived biennial cover crops as an alternative to mechanical tillage and herbicide applications for under-vine weed control. This study aimed to evaluate the effects of the under-vine cover crops red fescue (Festuca rubra), wild thyme (Thymus serpyllum), black medic (Medicago lupulina), and a commercial herb mixture in comparison to spontaneous vegetation, mechanical tillage and herbicide treatments on weed suppression, soil conditions, and grapevine performance in a non-irrigated vineyard with a cool to moderate climate. To assess the impact of the different treatments, soil vegetation coverage, soil moisture, and soil temperature were measured. Grapevine performance was evaluated in terms of yield, berry weight, must composition, cluster looseness, and bunch rot infection levels caused by Botrytis cinerea. Under-vine cover crops effectively suppressed weed growth over time, reducing overall weed cover to levels comparable to mechanical tillage and herbicide treatments. Further, they influenced soil conditions by increasing soil moisture and reducing soil temperature extremes at a depth of 6 cm. During the vegetation period in 2023, soil moisture levels were lowest with mechanical tillage. In contrast, the use of cover crops, such as red fescue, helped to maintain higher soil moisture levels over time and significantly lowered soil temperatures compared to herbicide treatments. Cover crop treatments resulted in looser cluster architecture, which was associated with a lower incidence and severity of Botrytisbunch rot. The highest disease levels occurred in herbicide-treated plots in 2024. Yield, must composition and berry weight were unaffected by the treatments, except that herbicide application resulted in significantly higher yield compared to under-vine cover cropping with wild thyme, which may indicate competition between wild thyme and grapevines for resources. The results suggest that under-vine cover crops offer several agronomic benefits, including improved moisture retention, regulation of soil temperature and reduced disease pressure, making them a viable alternative for sustainable vineyard management. However, potential trade-offs between yield and long-term soil conservation should be considered when implementing this practice.