About our vineyard cover crops series
In this Vineyard Cover Crops series, we’re evaluating three under-vine cover crop species for use in Minnesota vineyards. This week we’re taking a look at white clover, and how its use as a cover crop affects various aspects of a vineyard.
Previous posts in this series:
- Vineyard cover crops, part 1: An overview
- Vineyard cover crops, part 2: Buckwheat
- Vineyard cover crops, part 3: White clover
Ryegrass effects on grape quality
The University of Minnesota has developed an array of cold hardy ryegrass varieties, and though they are commonly found in the inter-row space of Minnesota vineyards, they have yet to be evaluated for under vine growth. In humid climates outside of Minnesota, Ryegrass is an effective cover crop for reducing vine vigor, reducing titratable acidity and increasing the degree of brix in grape must (Caspari et al. 1997). These effects are very desirable in Minnesota, where the cool climate hinders fruit ripening, resulting in grape musts with high acidity and low sugar content (Falconer et al. 2016).
Ryegrass effects on vineyard temperatures
Perennial ryegrass can reach heights of 1-2 feet (Ogle 2018), This height in concert with the density of the growth would impede air drainage and increase spring and fall frost risk if left uncut (Bugg et al. 1975; Falconer et al. 2016). Therefore, ryegrass plantings should undergo regular mowing well before these heights are reached. During the summer, ryegrass has a high rate of water consumption and forms dense stands (Schiedel 2016; Giese et al. 2014; Caspari et al. 1997), which will decrease field temperatures due to evaporation (Bugg et al. 1975).
Ryegrass’ thick stands also have an insulating effect on soils, which keeps soils cool during the hot summer months, and warm into the fall (Meng et al. 2009). In the spring this lag in temperature changes may increase frost risk, and an insulated soil would radiate less heat on cool nights (Bugg et al. 1975). The same attribute is beneficial in Minnesota as it prolongs grape maturation into the fall (Lecourieux et al. 2017). Depending on the site in question, ryegrass can have positive or negative effects on the vineyard microclimate, and careful consideration should be given to the pitfalls of one's site and how ryegrass will influence those concerns.
Ryegrass interactions with soil nutrients and water
Ryegrass has high nutrient and water demands, which can reduce the vigor of grapevines (Giese et al. 2014; Guerra and Steenwerth 2011; Caspari et al. 1997). It has been observed in humid climates similar to Minnesota, that ryegrass plantings have reduced the weight of summer and winter pruning growth by as much as 80% in excessively vigorous sites (Caspari et al. 1997). This effect can be greatly beneficial in vineyards over the southern and western portion of the state where soils are most fertile. Due to ryegrass’ wide range of suitable soil conditions for growth (Schiedel 2016; Ogle 2018), Ryegrass Can be useful in numerous soils across the state. Ryegrass Can be used in clay-heavy soils to increase the water deficit, overly fertile soils to reduce available nitrogen, or nearly anywhere else to address issues of excess. Although ryegrass should only be used in soils where nutrients are abundant, it can be beneficial in a range of soil moisture conditions (Guerra and Steenwerth 2011); it has proven to be a weak competitor with vines for water in less humid environments (Giese et al. 2014), but can also remove excess water in more humid climates (Caspari et al. 1997). This means that ryegrass can be advantageous in both the wet fertile aquolls and udolls of the south west, but also in the drier yet equally fertile alfisols found in the southeast and central portion of the state (Anderson et al. 2018).
Ryegrass vs. weeds
Due to ryegrass’ high soil moisture and nutrient requirements, fast growth rate, and seedling vigor, ryegrass Is very competitive and successful at weed suppression (Schiedel 2016; Ogle 2018; Bugg et al. 1975). Though a dense planting of Ryegrass can block other weeds from developing, it may take overseeding the land to fully establish ryegrass (Elford et al. 2008). Unlike buckwheat which is allelopathic and a better competitor for light, or white clover which spreads by stolons and also shades the soil, ryegrass does not smother other crops and only competes with other plants for nutrients once it is seeded; yet once established it has higher nutrient requirements and can be a more effective competitor (Schiedel 2016; Bugg et al. 1975).
Ryegrass erosion control
Ryegrass Forms a very dense patch and has extremely fibrous shallow root structure (Guerra and Steenwerth 2011; Bugg et al. 1975). This is a great benefit of using ryegrass in vineyards, because the concerns around under vine erosion are isolated to hortonian flow and shallow soil water movement, which a fibrous root structure is great at preventing (Bugg et al. 1975).
Ryegrass interactions with pests and diseases
Ryegrass is not greatly beneficial for vineyard IPM. It does a poor job of choking out other weeks, unless it is densely seeded. It can form a dense sod layer which can host various vineyard pests at different stages of their life cycle. Although there may be a moderate contribution to soil organic matter and a healthy soil biome, there will be a presumably lower mulching rate annually when compared to buckwheat or white clover.
The verdict on ryegrass as an undervine cover crop in Minnesota
Perennial ryegrass is best suited for established vineyard that:
- Are looking to use ryegrasses high nutrient demands to curb excessive vigor
- Struggle to reduce soil moisture in wet or moderate soils, clays, loams, or soils with high organic matter, contributing to vigor or “wet feet”
- Ryegrass’ advantages are best observed in the fertile alfisols of the south east and the mollisols of the south west, but only on sites with excessive vigor.
Bugg, Robert L et al. 1975. Cover Cropping in Vineyards. University of California Cooperative Extension Amador County.
Caspari, H. W., S. Neal, and A. Naylor. 1997. Cover Crop Management in Vineyards to Enhance Deficit Irrigation in a Humid Climate. Acta Horticulturae.
Elford, Evan M.A., François J. Tardif, Darren E. Robinson, and Eric M. Lyons. 2008. Effect of Perennial Ryegrass Overseeding on Weed Suppression and Sward Composition. Weed Technology.
Falconer, John, Mark Hart, and Ron Barnes. 2016. Growing Grapes In Minnesota. The Minnesota Grape Growers Association.
Giese, Gill et al. 2014. Complete Vineyard Floor Cover Crops Favorably Limit Grapevine Vegetative Growth. Scientia Horticulturae.
Guerra, Bibiana, and Kerri Steenwerth. 2011. Influence of Floor Management Technique on Grapevine Growth, Disease Pressure, and Juice and Wine Composition: A Review. American Journal of Enology and Viticulture.
Lecourieux, Fatma et al. 2017. Dissecting the Biochemical and Transcriptomic Effects of a Locally Applied Heat Treatment on Developing Cabernet Sauvignon Grape Berries. Frontiers in Plant Science.
Carroll, J., T. Weigle. 2021. Organic Production and IPM Guide for Grapes. New York State IPM Program.
Anderson, J., J. Bell, T. Cooper, D. Grigal. 2018. Soil Orders and Suborders in Minnesota. University of Minnesota Extension.
Jayden Corliss is a graduating CFANS student contributing these articles for credit as a distance learning substitute for a field course. Jayden is an assistant winemaker at North Shore Winery.
Thanks to Dr. Emily Hoover and Emily Tepe for their contributions to this article.