Growing quality grapes for wine making should take into consideration the entire ecosystem as part of a sustainable production system.
Vineyard floor management can have a large impact on the abiotic (e.g., temperature, wind, precipitation) and biotic (e.g., beneficial insects, pests, disease) factors in the vineyard, especially microclimate modifications and soil health. Decisions about what system to use should take into account the overall vineyard management system.
Vineyard sites may require cover crops that help in vigour control, compete with the existing weed population and control soil erosion by wind and water. Keep in mind that sustainable grape production must also consider labour concerns, economics of the management system and ecological impacts.
While this option requires little input, this system has both advantages and disadvantages. Resident vegetation consists of all plant species that are growing within the vine row and alleyways. These plant species can consist of both native plants and invasive weed species, with the diversity of native plant species determined by individual regions of viticulture production.
Management of resident vegetation usually consists of mowing to reduce plant height for vineyard traffic. Mowing frequency will be determined by the type of plant species present in the resident vineyard vegetation. In vineyards using conventional or sustainable systems, the area under the vine may be kept weed free with an herbicide application in the spring.
This system has minimal costs — primarily equipment costs to occasionally mow vegetation.
In conventionally managed systems, vineyard alley rows are disked or sprayed with herbicides to reduce in-row vegetation, while in organically farmed systems, mechanical means or approved organic products are used to keep vineyard rows weed free.
This can result in the exposure of bare soil, which will reduce competition with the grapevine for water and nutrients but can increase the possibility of wind and/or water erosion in prone areas. Slopes are particularly vulnerable to topsoil loss in clean cultivated systems.
Tillage and equipment travel through vineyard alleys over time can contribute to root zone compaction and problems with water infiltration.
Cover crops can be managed in a number of different ways in the vineyard. Most commonly, crops are seeded in every alleyway to provide cover throughout the vineyard. They can also be planted in alternate rows, each with a solid stand of a different cover (e.g., grass and legume) or simply clean cultivation in one alley row and a cover crop in the adjacent alleyway.
In some vineyards using sustainable management, the area immediately underneath the vine is kept clean with herbicide applications or cultivation to reduce any possible impacts on vine growth from competition for water and nutrients, especially with drip irrigated systems. Those vineyards with an organic management strategy must utilize mechanical means, due to strict regulations regarding the application of synthetic chemicals.
Depending upon the cover crop choice, tillage or mowing may be required.
Annual cover crops such as a number of grass and grain covers may need to be mowed a couple of times per year in order to facilitate access throughout the vineyard or for frost protection in the spring. Tillage is another option, especially for some annual legumes and forbs that can release nitrogen in the soil and may be available for vine uptake. However, timing of tillage and knowing the decomposition rate is important to ensure that nitrogen release coincides with an appropriate vine growth stage.
With perennial cover crop systems, mowing may also be necessary as some cover crops can reach heights of three feet. Tillage can also be applied to perennial cover crop systems as stands diminish and need to be reseeded.
Benefits
Potential problems
Floor management systems, particularly cover cropping, can impart a number of benefits to the production of premium quality grapes.
Vineyard age should be considered, as vigorous cover crops can compete with young vines for water and nutrients. This can reduce vine growth and possibly delay vine development in the early stages of establishment. Once a vineyard is established and vines are mature (> 4 years old), cover crops may be used in areas of excessive vigour to reduce canopy size and maintain an optimal balance between the vegetative and fruiting sections of the vine.
One of the biggest impacts of cover crops is the protection of the soil surface. Wind and water erosion can strip the upper soil layers, up to 5 cm in a growing season. Conversely, soil accumulates in areas that contain vegetative cover. Cover crops, especially grasses, protect the soil by minimizing the dislodging impact of raindrops and reducing water runoff.
During the growing season, cover crops can help to reduce soil compaction and soil erosion from equipment traffic and increase traction for vineyard traffic. This can be especially important when Pacific Northwest harvesting extends later into the autumn season, after precipitation begins to fall.
Cover crops can also reduce surface crusting and improve rainfall penetration, important on soils that may be subject to saline conditions or with higher percentages of clay. Those plant species with large root systems, like oilseed radish (Raphanus sativus or R. sativus var. oleiferus), have been proven successful at penetrating hard pans to improve water infiltration and drainage. Plants with extensive root systems aerate the soil as roots decompose, leaving pores that can increase infiltration.
Increasing soil organic matter and nutrient availability is a popular reason for utilizing cover crops in vineyards.
However, the impact of cover crops on actual levels of organic matter and its use to solely supply nutrients to the vines is highly dependent upon the soil type, temperature and rainfall. Many of the microorganisms involved in the decomposition of organic material need some type of moisture to maintain their activity. Therefore, in semi-arid and arid regions, it is very difficult to greatly affect the percentage of organic matter in the root zone unless there is supplemental irrigation in the vineyard alleys.
Mycorrhizal fungi are symbiotic fungi, also known as arbuscular mycorrhizal fungi (AMF) that colonize grapevine roots. Be cautious when using mycorrhizal supplements as existing research under field conditions has not definitively shown consistent benefits. If you do choose to use mycorrhizal supplements, be sure that the source is a reputable vendor and that some type of plant material is part of the supplement.
Mycorrhizae require living roots in order to grow and reproduce. It may be fairly expensive to inoculate an entire vineyard with AMF, thus inoculating individual vines when establishing a vineyard is more practical.
Mycorrhizae can improve water status in grapevines and has been shown to increase some nutrients in other crops, a benefit for vineyard sites with marginal soil status. Simply the presence of a cover crop can increase the population of vesicular arbuscular mycorrhizae (VAM) fungi in vine alleys. However, colonization of grapevine roots by VAM requires that the roots be in contact with the colonized cover crop roots in vine alleys, although there is some colonization by other types of mycorrhizal fungi.
Planting a cover crop that is a host for AMF fungi has been shown to boost resident populations in other crops, but research in vineyards is limited.
To gain the most benefit from mycorrhizal inoculations, do not fumigate prior to planting (unless there is a preexisting condition necessitating fumigation), reduce high inputs of phosphorus fertilizers and reduce tillage practices to avoid disrupting existing AMF colonies.
Insect populations can be increased or decreased, depending upon cover crop choice.
For example, some vineyard pests (e.g., cutworms) prefer broad leaved covers rather than grasses, and the presence of broadleaf covers in the alleyway can reduce the number of bud strikes observed during the early spring season. Having some type of cover can also aid in reducing dust and spider mite populations, as dusty, dry conditions encourage these populations.
However, cover crops can also increase populations of certain vineyard pests, especially voles, moles, and gophers.
Different cover crop choices may require different methods of seeding. However, seed bed preparation is fairly standard.
Choosing a cover crop will depend largely upon the objectives that you want to address in the overall vineyard management plan. There are three main categories of cover crops: grasses, legumes and forbs.
Many grasses tend to form a large, fibrous root system, which is beneficial in windy areas to prevent soil erosion. In vigorous vineyards, it can take up nitrogen and tie it up over time. Unlike legumes, nitrogen in grass plants is not readily available to vines for uptake when the plants decompose.
Grass cover crops can provide a substantial amount of biomass that, over time, may aid in increasing vineyard soil organic matter.
Grasses like cereal rye, oats, barley and triticale are often used as annual cover crop systems. Typically, these are planted in the autumn and tilled under or mowed in the spring for frost protection. Mowing grasses can leave stubble in the vineyard alleys, which can reduce dust, provide traction for field equipment and compete with weed species. Grasses are usually more competitive than legumes or forbs with existing weed populations.
Legumes are broad leaved, annual or perennial species that are known for their ability to fix nitrogen. Nodules colonized on the roots are the factories that house nitrogen-fixing bacteria (Rhizobium spp.) that form a symbiotic relationship with legume roots.
However, legume seeds must be inoculated with the proper strain of bacteria in order to effectively fix the nitrogen. Nodules that are actively fixing nitrogen will appear pink when cut in half. Nitrogen is released and available for mineralization processes after the cover crop begins to decompose.
When legumes are mowed, some of the roots die in order to keep the plant in balance between the shoot and root systems. Thus, a proportion of the colonized roots die and release nitrogen as well. Root systems of legumes have a taproot based system that can aid in increasing water infiltration.
Legumes can attract a number of rodents to the vineyard so are often used only in established vineyards to avoid damage to young root systems.
Forbs are broad leaved, flowering plants and can consist of annual and/or perennial species. A number of forb species make up wildflower mixes that are available from a local cover crop seed supplier. Forbs can be attractive, and some studies indicate that they may be able to increase beneficial insect populations, depending upon the diversity of species in the mix.
Wildflower mixes can be difficult to establish if the mix contains species that are not appropriate for the region in which the vineyard is located. Establishment can be enhanced by breaking up the soil prior to seeding or broadcast seeding. Seed contact with the soil surface is increased by running a ring roller through the vine alleys.
When using these mixes, be sure to contact your local extension agent or weed specialist to determine if any of the components may be listed on your province’s noxious weed lists. A number of introduced species have become noxious weeds in the past and are very difficult to control (e.g., Yellow Starthistle, Purple Loosestrife).
| Tilled | No-till | |
|---|---|---|
| Annual ryegrass | x | |
| Cereals (barley, oats, triticale, wheat) | x | |
| Cereal rye | x | |
| Clovers (crimson, rose, subterranean) | x | |
| Field pea | x | |
| Medics (bur, barrel, black) | x | |
| Mustards | x | |
| Vetches | x |
Annual ryegrass (Lolium multiflorum) — Annual ryegrass is also known as Italian ryegrass and is a cool-season bunch grass. As with many of the grasses, it has an extensive fibrous root system, useful in areas with excess water or nitrogen. In vineyards with marginal nutrient status, annual ryegrass can compete with the vine during bloom and early shoot growth. This grass is quicker to form a good stand than perennial ryegrass, which is slower to establish. Annual ryegrass tends to perform better on finer textured soils (e.g., silty or clay), although sandy soils may be adequate for growth. Annual ryegrass matures between June and September and is typically seeded in the autumn and tilled in late spring or early summer.
Cereal cover crops — Barley (Hordeum vulgare), oats (Avena sativa), triticale (Triticosecale hexaploide) and wheat (Triticum aestivum) are known as cereal cover crops and can be interplanted with vetches because their stems are often strong enough to support the vine-like growth. Care should be taken when choosing varieties that are resistant to diseases that could infect nearby fields of grain crops. Barley and wheat are more drought tolerant than oats or triticale. Cereal crops are often tilled into the vineyard in early summer but can be mowed for extra frost protection in the spring. Cereal crops form a fibrous root system, adequate for reducing soil erosion and removing excess nitrogen. Cereal crops are planted in the autumn to take advantage of winter moisture for germination.
Cereal rye (Secale cereale L.) — Cereal rye or winter rye can be used to increase organic matter and can produce about 3,500-11,000 kg/ha in dry biomass. It has an extensive fibrous root system that can take up excess water and nitrogen present in the vineyard. It can be combined with any of the vetch species to increase residue in vine alleys and can be helpful to degrade certain herbicide residues. It is normally planted in the autumn or early spring and mowed before it begins to senesce. Cereal rye is a very cold tolerant cover crop, enduring temperatures down to -34°C.
Clovers — Crimson clover (Trifolium incarnatum), rose clover (Trifolium hirtum) and subterranean clover (Trifolium subterraneum) are annual clovers often used in vineyards that are managed without tillage. Crimson and rose clovers can reach a height of 15-20 cm. However, subterranean clovers exhibit a low, prostrate growth habit. Unlike other clover species, subterranean clovers produce seed underground, perhaps lending some advantage to providing a continual stand. As with many clovers and medics, a large quantity of hard seed is produced that will germinate over multiple years. Clovers perform best when part of a mix, especially including multiple clover and medic species. In soils with poor nutrition, it may be difficult to establish a good stand, so adequate phosphorus, calcium and sulfur are necessary. Amendment of the soil before planting can ensure good establishment.
Field pea (Pisum sativum) — Field pea has been used in a number of vineyards in the eastern Pacific Northwest as a winter/spring annual and tilled or mowed in early summer to supply organic matter and release nitrogen. Stems of the plant are succulent and break down rapidly, providing a burst of nitrogen in the soil. Much of the biomass is accumulated in the early spring and is often a component of cereal crop mixes.
Medics (Medicago spp.) — Bur medic (Medicago polymorpha), barrel medic (Medicago truncatula) and black medic (Medicago lupulina) are cover crops that were originally used for establishing pastures. All are considered a reseeding annual or a short-lived perennial. Bur medic performs well on soils with pH > 6.5, establishes with relatively little seed (~5.5 kg/ha) and produces large quantities of hard seed for growth in future season. Seed pods from bur medics are often spiny, although some cultivars, such as Santiago, have no spines on seed pods. Bur medic performs well in vineyards with minimal irrigation in vine alleys, provided winter rains are adequate. Barrel medic prefers soil pHs that range from neutral to alkaline and requires about 300 mm of precipitation to adequately establish. It too produces a large number of hard seeds, maturing in mid-spring. Black medic performs well on soils similar to barrel and bur medic. The cultivar George was developed for dryland production with approximately 375 mm of precipitation per year. It is easily controlled with mowing and herbicide applications.
Mustards (Brassica spp.) — Mustards are part of the forbs family and are often grown for their ability to produce certain chemicals called glucosinolates. These compounds break down via microbial degradation to isothiocyanide, which can act as a soil fumigant and weed suppressant. Mustard cover crops can be grown and incorporated before a vineyard is established if a chemical fumigant is not desired. If grown in vine alleys in an established vineyard, it is treated as a reseeding annual and should not be mowed until seeds have set. Both white mustard (Sinapsis alba) and oriental mustard (Brassica juncea) have shown success in drier environments. Brassica napus can also be grown as a cover crop. However, it is mainly grown for oilseed production.
Vetches (Vicia spp.) — This group of covers include hairy vetch (Vicia viiosa) and common vetch (Vicia sativa). Vetches are commonly seeded or are present as volunteer plants in vineyards. They can be seeded in stands alone or with grain crops to provide a structure for climbing. Hairy vetch is more prone to climbing beyond the vine alley, into trellises, especially on deep soils. Vetches are fairly shallow rooted plants, unlike many of the taprooted legumes. Both types of vetches have bluish-purple flowers during bloom and can be an effective cover for attracting beneficial insect populations as well as pure aesthetics. Hairy vetch is more cold tolerant than common vetch, with most of the biomass production in the early spring and summer. Allow vetches to reseed if a continuous stand is desired.
Fescues (Festuca spp.) — This group includes tall fescue (Festuca arundinacea), sheep or hard fescue (Festuca ovina) and red fescue (Festuca rubra). Sheep and hard fescues are bunchgrasses, while red fescues can have a slow, spreading growth habit. Many turf type fescues can form a dense mat of growth in vine alleys, providing excellent weed suppression and traction. During the summer, the reduction in precipitation and/or irrigation will induce dormancy, providing a layer of mulch. Fescues are well suited for dryland vineyards and should be autumn-seeded to take advantage of available precipitation. Some varieties of fescue can produce large root systems, which may make them difficult to eradicate. Most fescues are prolific seed producers which will contribute to the following season’s stand.
Indian ricegrass (Orzyopsis hymenoides or Achnatherum hymenoides) — This grass is native to western North America and is often used for erosion control on sand dunes and soils with large percentages of sand. Although green in the spring, it is a summer dormant species that retains its hold on soil particles, making it useful for sandy, windy sites. It is a very drought tolerant, cool season cover crop choice.
Meadow barley (Hordeum brachyantherum) — Meadow barley is a perennial grass that performs best in wetland or riparian areas. It is also known as California barley and can tolerate clay with low calcium and low water holding capacity or serpentine (high magnesium) soils. Serpentine soils are most commonly found in California and not readily found in the Pacific Northwest. Meadow barley is a poor competitor with weeds, and some type of control measure should be taken before planting meadow barley.
Perennial ryegrass (Lolium perenne) — Perennial rye is a cool season, moderately drought tolerant bunchgrass that can be competitive when overseeded. It establishes relatively quickly and germinates early in the growing season. Because of its early germination, it is an ideal candidate for grass mixes in which the germination of other species is staggered. This will provide a green cover for a longer period during the growing season than a monoculture of perennial rye. Perennial rye is especially good for preventing soil erosion because of its extensive fibrous root system. In areas with mild winters, perennial rye can be seeded into vineyard rows. In areas with potentially cold winters, it should be seeded during the late summer. Seeds should not be planted deeper than 1.25 cm to establish a good stand.
Wheatgrasses — This group of grasses includes crested wheatgrass (Agropyron cristatum), standard crested wheatgrass (Agropyron desertorum), pubescent wheatgrass (Agropyron trichophorum) and a number of other species. These grasses are known for their drought tolerance and persistent stand (5-7 years). With good early establishment, they can significantly reduce the weed population in vineyard alleys. They can be seeded in combination with forb mixes to aid in attracting beneficial insect populations, but be careful of competition with forbs in establishment.
White clover (Trifolium repens) — White clover is a perennial cover that performs better on heavy soils than on lighter, sandy soils because it is not as drought tolerant as other clovers like subterranean clovers. It is considered a short lived perennial that may require replanting every 3-4 years, depending upon stand establishment. Plants are hardy to about -8°C. White clover seeds are small and seed/soil contact must be maximized to get good stand establishment. Seeding depth should be no more than 0.5 cm, thus a properly prepared seed bed is required.
Wildflower and forb mixes — These mixes often consist of various varieties of native flower and grasses to enhance ecological diversity. Choosing native varieties will ensure sufficient germination and persistence from year to year. Check with your local extension or agriculture office to get a list of native wildflowers for your area. Also be sure to inquire about any component of the mixture that may become an invasive species. A mixture of species may necessitate a broadcast application within the vineyard rows due to the variance in seed size. After broadcast seeding, a press wheel or cultipacker may be useful to maximize the seed/soil contact. However, seeds should not be pressed into the soil too deeply.
This listing is not an endorsement for a particular vendor.
