COVER CROP GRASS FOR VINEYARDS
Cover crops were frequently planted in order to reduce erosion, add nitrogen, and improve soil tilth and water penetration. Winter annual grains or legumes or both were planted in the fall and then mowed and disked in the early spring. Now a days cover cropping in vineyards experienced a widespread resurgence as a result of the growing interest in sustainable agriculture. New cover crop species and cultivars, tractor implements, and irrigation methods have allowed many growers to adopt new cover cropping techniques to meet today’s needs.
- When should I cut my vineyard cover crop?: The cover crop is often disked or mowed in late March if there is a danger of frost. If re-seeding is desired, incorporation may be delayed until the cover crop sets mature seed. Permanent perennial cover crops that grow during the summer usually compete strongly with vines for soil nutrients and water.
- Why are cover crops planted between rows of grape vines?: Cover crops are grown between vine rows for many reasons. To protect the soil, prevent erosion, suppress weeds and provide nutrition. They also support integrated pest management by increasing biodiversity, supporting pest predators and providing a natural nutrient cycling system to enhance soil and vine health.
- What is the purpose of a cover crop?: A cover crop slows the velocity of runoff from rainfall and snowmelt, reducing soil loss due to sheet and rill erosion. Over time, a cover crop regimen will increase soil organic matter, leading to improvements in soil structure, stability, and increased moisture and nutrient holding capacity for plant growth.
- What can you plant between vineyard rows?: In viticulture, cover cropping refers to crop planting between and under the rows of vines, in order to improve the management of the vineyard. Cover cropping is no new invention, even though lately with the increased interest in organic and sustainable viticulture, there is a lot of buzz about that topic.
MOVING AND SWARD MANAGEMENT
Timely mowing can improve and enhance cover crop establishment and performance. Mowing removes taller weeds that can shade the cover crop. This is critical for the growth of some species. Mowing also encourages tillering (the growth of shoots from the crown of the plant), spreading, and flowering. Many cover crop species are also pasture forages, which typically respond to grazing by increasing the number of shoots from the crown to quickly regrow and crowd out competition.
The first mowing should be no lower than 4 to 6 inches tall in order not to injure desired plants. This mowing can also help to shred vine prunings. Perennial grasses should be mowed early in the growing season to prevent the seed set of tall weeds, chop the prunings into the cover crop, and reduce the hazard of frost. Fertilizing after mowing stimulates the grasses and helps maintain a dense, healthysward that resists invasion by weeds.
Perennial grasses should be allowed to flower in late spring. Before flowering, thegrasses typically go through a cycle of rapid growth followed by a period in which carbohydrates are accumulated in the root system. These reserves allow them to withstand summer drought better and recover during fall rains or irrigation. Some native grasses are especially sensitive to decline if they are not allowed to grow, flower, and remain green for several weeks after flowering in late spring.
Native bunchgrasses should be mowed no lower than 6 to 8 inches. Mowing too low can kill these plants. In areas prone to frost, cover crops should be mowed close to the ground to minimize frost hazards and reduce the migration of icenucleating bacteria from the cover crops onto grape foliage. The closer the cover crop canopy is to the grapevines and the more surface area that the cover crop has, the more likely it is that ice-nucleating bacteria will be present in large numbers and will migrate to the emerging grapevine shoots, increasing the risk of damage if freezing temperatures occur.
PEST MANAGEMENT OBJECTIVES
Cover crops can provide several features for beneficial insects, including extrafloral nectaries, habitat for prey, and protection from predators. Grower experiences sugest that even allowing naturalized weed species to grow and mowing them all season long can lessen pest pressures from leafhoppers and spider mites. Some cover crop species compete intensely with weeds and can dramatically suppress their growth. When properly managed, many of the grasses are extremelycompetitive, especially annual and perennial ryegrasses.
The impact of cover crops on nematodes is not well understood. Tests conducted on containerized cover crop plants indicate that many cover crop species are also good hosts for nematodes known to parasitize grapevines. Although anecdotal information suggests that nematode damage to vines may be reduced, more research is needed to address this issue. ‘Cahaba White’ vetch has been shown to suppress nematodes in grapevines, and various mustards have been shown to suppress nematodes in other crops. Unfortunately, knowledge of how to use cover crops as a pest management tool for nematode supression is limited.
Vertebrate pests may also be influenced by cover crops and their management. Pests such as meadow voles, gophers, rabbits, and moles are attracted to areas planted with cover crops, which can offer these pests shelter from predators. Voles and gophers can do considerable damage to a vineyard if left unmanaged. Low-growing cover crops, mowing, and vegetation-free strips beneath vines can minimize the habitat available for these pests and reduce the damage to vines.
TYPES OF COVER CROPS
Many types of plants can be used as cover crops. Grasses (including cereals) and legumes and are the most extensively used, but there is increasing interest in brassicas (such as rape, mustard, and forage radish) and continued interest in others, such as buckwheat. Choosing a cover crop depends largely upon the objectives in the overall vineyard management plan.
Vineyard manager has a tremendous plant palette from which to choose when selecting cover crop species. Just as there is no universal wine grape cultivar, rootstock, or trellis system, there is no universal cover crop for all vineyards. The choice of cover crop systems depends largely on the benefits one hopes to attain from the cover crop. Cover crops should be chosen on their suitabilityfor a production system and the style of farming that the manager wishes to use.
The cover crop’s physical stature, water use, competition with vines, and ease of establishment and maintenance are only a few reasons why they should be chosen carefully. There are numerous benefits to planting cover crops, and growers are encouraged to experiment on a small scale first to determine whether a particular species or management system is appropriate.
Grapevines have fewer mineral deficiency problems and fertilizer demands than many other horticultural crops and is adaptable to a wide range of soil types and soil fertility. In general, only four nutrients, nitrogen (N), potassium (K), zinc (Zn), and boron (B) are widely supplemented in vineyards. Local areas may require additional phosphorus (P), iron (Fe), magnesium (Mg), and manganese (Mn).
- Legumes: are broad-leaved, annual or perennial species known for their ability to fix atmospheric nitrogen (inert gas) into usable forms. Nodules on the roots are the “factories” that house nitrogen-fixing bacteria (Rhizobium spp.) that form a symbiotic relationship with legume roots. Nitrogen accumulations by leguminous cover crops range from 40 to 200 pounds (18 to 90 kg) of nitrogen per acre. The portion of green-manure nitrogen available to grapevines is usually about 40 to 60 percent of the total amount contained in the legume. If growing legumes it is better to incorporate them into the soil when they are blooming to get the maximum addition of nitrogen.
Cool season (winter) annual legumes are generally planted in the fall and provide forage in late fall and spring. These plants flower and produce seed in late spring and die soon after seeds mature. Cool season annual legumes differ substantially in their preferred soil characteristics, growth distribution, cold tolerance, bloat potential, and reseeding potential.
- Grasses: cover crops produce high biomass and dense fibrous root systems preventing soil erosion. Grasses are higher in carbon than legume cover crops. Because of their high carbon content, grasses break down more slowly than legumes, resulting in longer-lasting residue. As grasses mature, the carbon to nitrogen ratio (C:N) increases. This has two tangible results, the higher carbon residue is harder for soil microbes to break down, so the process takes longer, and the nutrients contained in the cover crop residue usually are less available to the grapevines.
Grasses are often described by their growth cycle through a year: cool season and warm season grasses. The main growing period for cool-season grass is in spring and fall when soil temperature is 50 to 65 degrees F (10 to 18°C), and the air temperature is 60 to 75 degrees F (16 to 24°C).
- Brassicas: used as cover crops include mustard, rapeseed, and forage radish. They are increasingly used as winter or rotational cover crops in vegetable and specialty crop production, such as potatoes and tree fruits. Rapeseed, also known as rape, grows well under the moist and cool conditions of late fall, when other kinds of plants are going dormant for winter.
- Buckwheat: is a summer annual that is easily killed by frost. It will grow better than many other cover crops on low-fertility soils.
