Patty Skinkis, Oregon State University
There are a number of goals when determining how to manage the vineyard floor between vines, in the vine row, and in headlands around vineyard blocks. The most important goals are related to weed control, soil conservation, and soil water management. Differences in vineyard floor management must take into consideration the age of the vine, vineyard design, soil type, and growing region.
Weed populations in the vineyard should be managed from the pre-establishment stage through the vineyard development and management phases. The priority before planting is to eliminate or reduce invasive or perennial weeds that will be a management concern long-term and will compete with young vines. Once the vineyard is planted, weed control is vital to ensure that the young vine can grow without competition for soil moisture and nutrients. Since root systems of young vines are small and have more limited access to soil moisture, weed control is critical to allow proper establishment.
Once the vineyard is established, weeds need to be managed to reduce competition for soil moisture and nutrients. While limiting competition is important throughout the growing season, it is particularly critical between bloom and veraison. It is during this period that the vine is developing its canopy, and heat during the warmest part of the season increases the vine's evapo-transpirative demand for water. Managing vine water relations during this period (either excess or deficit) has a strong impact on vine growth and canopy development, and weeds may need to be managed to avoid increasing vineyard water demands.
There are several methods by which weeds can be managed, including the use of herbicides or tillage. Contact your local Extension agent, farm advisor, or consultant for more information on herbicides that can be used in the vineyard, or visit the reference sources listed below. There are advantages to both aspects of weed control. The appropriate use of herbicides in the vine row can reduce production costs, tractor time, and fuel use associated with mechanical tillage methods of weed control. Conversely, management of weeds through tillage allows for a non-chemical method of weed control which is accepted in organic programs.
It is important to preserve and enhance the soil in any agricultural setting, and you can use cover crops to prevent soil erosion and alter soil properties in a beneficial way. Cover crops refer to vegetation grown in the alley between vine rows. Benefits of cover crops are many, and the benefits depend on what species are planted and whether they are annual or perennial. Perennial cover crops, such as grass species, are commonly planted in established vineyards to facilitate worker and tractor movement. Grasses can also prevent nitrate leaching in soil and help to reduce soil erosion significantly. In regions with dry summers, grasses go quiescent (a state of dormancy) and do not compete aggressively for water during the season. In non-irrigated production areas, cover crops can help manage excessive vine vigor by reducing excess soil moisture. The presence of permanent stands of cover crops reduces the need and frequency of tillage, allowing for the soil to remain relatively undisturbed. This allows for increased soil microbial populations, enhancement of beneficial mycorrhizal fungi, and increased soil aggregation and stability over time. Perennial legume cover crops also can add nitrogen into the system. In addition, permanent cover crops can allow for better water infiltration and reduced water runoff. These are particularly important factors in sloped vineyards or where soils may be eroded by significant wind or rain.
Annual cover crops are chosen for multiple reasons in vineyards. One reason to grow annual rather than perennial cover crops is to allow the cover crop to grow and provide seasonal soil conservation in winter and remove the cover crop by tillage in the dry season (summer). Secondly, seeds for annuals, particularly grains, are less expensive to establish than permanent grass or other more expensive annuals. Many annual flower species have also been used in the vineyard and often re-seed. Some annuals, particularly annual clovers or other legumes, can be grown as green manures to supplement nitrogen and other nutrients into the vineyard system. Several annual flower species can be grown to provide biodiversity and the potential to attract beneficial organisms such as predatory insects. Fall-seeded annual cover crops are often planted in vineyards of the East, Midwest, and Pacific Northwest. This allows vineyard managers to control soil erosion from winter rains/precipitation and remove the cover in the spring/summer.
Different vineyard floor management practices are used in regions with varying concerns over water resources. In areas that are arid, establishing cover crops may be difficult, and vineyard soils are often bare. Also in young vineyards, managers may choose to have no cover crop to avoid competition with the young vines. Depending on the row spacing, soil type and water resources (precipitation or irrigation), it may be possible - and desirable - to establish a cover crop in young vineyards, particularly if a zone within the vine row is kept free of vegetation. A good rule of thumb is to have the in-row zone no less than 3 feet in width.
Cover crops can be used to alter soil moisture. Depending on the vineyard site, cover crop species should be selected that are amenable to the specific soil moisture management goals. For example, shallow-rooted grasses are often used to reduce erosion of soils without causing water competition between the cover crop and the vines in warm, dry growing regions. Conversely, regions with significant soil moisture during the growing season may benefit from cover crops that can help reduce soil moisture and manage vine growth and vegetative vigor without providing excessive nutrient availability. In non-irrigated areas with seasonal variation in rainfall, cover crops or native vegetation is often adapted to wet and dry growing seasons to manage vine water relations. In dry years, cover crops can be killed with contact herbicides or tillage to conserve water, or allowed to grow to manage excess water availability in wet years. Grasses can also serve to reduce vine vigor by competing for water and nitrogen. In established vineyards with particularly high vine vegetative growth (vigor), grasses can be allowed to grow taller between mowings, allowing for development of a deeper root system, providing additional competition. Cover crops can also be used to increase water infiltration into the soil and prevent water run-off, particularly during rain events. Deep-rooted cover crops can be particularly useful in increasing water infiltration in heavy soils with high clay content. Read and review some of the resource documents for more information on cover crop planting species for your region and management goals.
Mulching with synthetic and organic mulches has been used in agricultural production to provide weed control or provide soil moisture conservation. You can use synthetic mulches such as polyvinyl sheets in the vine row to prevent weed growth, and these can be used in organic production systems. These mulches can break down over time and cause problems with equipment if not managed appropriately. Organic mulches can include the use of plant or animal biomass as a layer thick enough to provide soil moisture retention and enough limitation of sunlight to the soil surface to inhibit weed seed germination. Depending on the source of organic mulch, there can be changes in soil composition and nutrient availability.
Straw mulch from round bales is commonly used in the East to add organic matter and conserve moisture, particularly in higher production-oriented Concord and hybrid wine grape vineyards. Mulch is applied in the fall (often after harvest), typically in alternate row middles. This is done in alternating years. Vineyards using row-middle mulches typically see more consistent and higher production over time.
Vineyard floor management involves a number of different management practices. This review introduces you to some of those practices, and more details can be found in the resources provided. Furthermore, if a cover crop is to be grown, it is important to select a species or mix of species suited for your region and management goals.
Integrated Weed Management UC Pest Management Guidelines, University of California
Pacific Northwest Weed Management Handbook, Washington State University and Oregon State University
Cover Crop Selection and Management in Orchards and Vineyards, University of California-Davis
Cover Crops as a Vineyard Floor Management Strategy for Pacific Northwest Vineyards, Washington State University
Alternative Weed Management in New York Vineyards Sustainable Viticulture in the Northeast Newsletter #3, Cornell University
Vineyard Weed Management, Cornell University
Weed Management: Chapter 5 NY Guide to Sustainable Viticulture practices, Cornell University
Weed and Vineyard Floor Management Grape IPM in the Northeast, Cornell University
Vineyard Weed Identification PowerPoint, Michigan State University