Covering New Ground: Under Vine Cover Crops for Weed Management in Ontario Vineyards

by Matthew Lawford (summer student), Kathryn Carter, OMAFA, Stephanie Vickers, OMAFA

Weed management in commercial vineyards traditionally relies on the use of herbicides or cultivation in organic systems. However, growing concerns about herbicide resistance, limited availability of organically certified herbicides, and increased awareness of soil health has sparked interest in the use of under vine cover crops in vineyards.

Research from New York and Pennsylvania indicates that under vine cover crops can effectively suppress weeds and enhance soil health by improving soil structure, increasing soil organic carbon and microbial activity, reducing the risk of soil erosion (Vanden Heuval and M. Centinari, 2021), and minimizing nutrient run off (Karl et al, 2016). Additionally, under vine cover crops have been shown to help regulate vine vigour and improve vine balance.

Despite promising results in other regions, little research has been conducted on the suitability of under vine cover crops for Ontario vineyards. An ideal under vine cover crop should establish early, suppress weeds, maintain yield and fruit quality, and exhibit low growth habits to minimize impacts on canopy humidity.

A three-year research project was initiated in 2022, with the following objectives: 

• Conduct small-scale “screening” trials to identify cover crops species that perform well under vines in Ontario’s climatic conditions
• Implement large-scale trials to assess the impact of under vine cover crops on weed management, vine vigour, and soil health
• Develop practical methods for mechanically seeding under vine cover crops at a commercial vineyard scale

Field Trials in 2024

Small-scale screening trials were set up in 4 commercial vineyards (3 wine grapes and 1 table grape). Cover crops species included alfalfa, forage rapeseed (FR), crimson clover + forage rapeseed mix (CC+FR), crimson clover + white clover mix (CC+WC), forage chicory, subterranean clover (subclover) and lentils. The seeds were broadcast by hand under the vines and growth and establishment was monitored throughout the year. The large-scale trial treatments included grower management (herbicide), crimson clover + white clover mix (CC+WC), forage turnip (T), and crimson clover + forage turnip mix (CC+T). Seeds were mechanically seeded under the vine using a modified seed drill (Figure 1). Assessments were conducted to evaluate weed and cover crop populations, yields, fruit quality and vine health.

Figure 1 Mechanically seeding under vine cover crops using modified drill seeder

Lessons Learned from 2024

Screening Trials

There was considerable variability in cover crop performance across sites, likely due to differences in seeding timing, rainfall, and seed bed preparation. Overall, alfalfa, crimson clover + forage rapeseed (CC+FR) and crimson clover + white clover (CC+WC) exhibited the greatest establishment and growth among all treatments (Figure 2). In contrast, forage rapeseed and lentils established poorly and were quickly outcompeted by weeds. Chicory and subclover had moderate growth but did not suppress weed populations. As a perennial species, chicory overwintered but grew up into the fruiting zone in 2025, reducing air circulation within the canopy and increasing disease pressure. Other perennial cover crop species (alfalfa, CC+WC) also overwintered well, and their weed suppression performance was evaluated in 2025. The alfalfa that was seeded in 2023 (alfalfa23) appeared to reduce vine vigour more than the other cover crops, suggesting it may be too competitive for under vine use.

Figure 2 Establishment and growth (dry biomass) of cover crops and weeds in small plot screening trials in 2024. Error bars represent standard error. Letters indicate statistically significant differences (p < 0.05 ANOVA, Tukeys HSD).

Large Plot Trials

While the grower management treatment had fewer weeds, there were no significant differences in the weed populations among treatments (Figure 3). The crimson clover + turnip (CC+Turnip) mix had the highest cover crop establishment and biomass, whereas weed growth exceeded cover crop growth in both the crimson + white clover (CC+WC) and turnip treatments. This was likely due to a dry spring and delays in establishment. Post-harvest visual observations indicated that the crimson clover + white clover treatment continued to establish and successfully overwintered into 2025. The turnip treatments also overwintered successfully; however, being biennial, they bolted and the grew into the canopy in 2025. In all of the treatments, weed escapes and tall under vine cover crops required mowing to keep plants from growing into the canopy. Although grape yields were numerically higher in the grower management (herbicide) treatments, there were no statistical differences in yield, fruit quality, or vine vigour among the treatments. At one site, petiole nitrogen levels were low in under vine cover crop treatments at veraison, highlighting the need to monitor vine nutrient status.

Figure 3 Establishment and growth (dry biomass) of cover crops and weeds in large-scale mechanized seeding trial (August 2024).  Error bars represent standard error. Letters indicate statistically significant differences (p < 0.05 ANOVA, Tukeys HSD).

Take home messages

Mixed results from 2024 highlight that the suitability of under vine cover crops is highly site-specific. Key factors influencing successful establishment include soil texture, seedbed preparation, and rainfall following seeding. Trials conducted from 2022 – 2024 indicate that perennial cover crops offer the best opportunity for establishing and maintaining an under vine cover crop. This approach also reduces costs in subsequent years by minimizing seed and labour requirements. However, it is only suitable for vineyards that do not require hilling/dehilling.

Hilling and dehilling prior to seeding improved seed bed conditions for mechanical seeding and improved cover crop establishment.  The use of herbicide applications prior to seeding helped reduce weed pressure and enhanced cover crop establishment.

When selecting an under vine cover crop, it is important to consider site conditions and grape variety, as some cover crops can affect vine growth (eg. alfalfa). Avoid using cover crops that grow into the canopy to reduce the risk of fruit rots. In dry years, cover crops may compete for water and nutrients, so access to irrigation may be beneficial. Future research will evaluate the impact of under vine cover crops on soil health and soil moisture.

Resources

Karl, A. D., Merwin, I. A., Brown, M. G., Hervieux, R. A., & Vanden Heuvel, J. E. (2016). Under-vine Management Impacts Soil Properties and Leachate Composition in a New York State Vineyard. HortScience, 51(7), 941–949. https://doi.org/10.21273/HORTSCI.51.7.941

Vanden Heuvel, J., & Centinari, M. (2021). Under‑vine vegetation mitigates the impacts of excessive precipitation in vineyards. Frontiers in Plant Science, 12, 713135. DOI: 10.3389/fpls.2021.713135