Chapter 30

Cover Cropping in Vineyards

Criteria for Selecting Cover Crop Species

Proper choice and management of cover crops are important in maximizing the benefits and reducing potential problems in vineyards. To select a species or mix, the grower should first identify the purpose and objectives for its use. Subsequent factors to consider include seed availability, moisture requirements, crop rotation, and equipment for seeding and planting. Cover crop choice is important because different species provide different benefits. For example, small grains such as barley, oat, rye, triticale, and winter wheat may provide biomass for building soil organic matter and weed suppression. Some crops may also have allelopathic effects, where chemicals produced by the cover crop inhibit growth of weeds.

Relative Vigor of the Vineyard

Cover crops can reduce grapevine vigor, which can be either an asset or a liability, depending on available moisture, vine size, and available nutrients. In cases where vine growth in vineyards is vigorous, dense sod-forming grasses such as turf-type tall fescue and perennial rye grass may be grown to reduce excessive vine growth.

Frost Hazard

Under such stratified air temperature conditions vines trained lower to the ground are more prone to experience colder temperatures. This factor needs to be kept in mind as it is becoming fairly common in some areas for growers to train the vines to very low heights, and in so doing the frost-prone tissues are often less than two feet above the ground surface.

Nitrogen Contribution

Growing legumes (e.g., peas, vetches, clovers, or beans) is one of the most important tools to increase soil fertility. Legumes fix nitrogen from the atmosphere and make it available in the soil to other plants.

Soil Erosion Considerations

Soil erosion should be an important consideration for anyone growing grapevines planted on slopes. For maximum erosion control, the best cover would be vigorous perennial grasses that form a dense root system, such as ryegrass or tall fescue.

Soil Moisture Availability

In the case of dryland vineyards, or those receiving minimal irrigation, perennial cover crops are not usually recommended because soil water needs to be conserved during summer. Winter annuals would be a better option in many vineyards, which in spring are mowed. Winter annuals that require relatively small amounts of moisture to germinate and grow include cereals, field pea, vetch, and bur medic (Ingels et al., 1998).

Improve Soil Structure

Increasing soil organic matter improves soil physical properties through a complex process. As plant residues degrade, the soil microbes feeding on them release gluelike compounds into the soil (gums, waxes, and other substances and exudates), which cement soil particles together to form stable soil aggregates, resulting in improved soil structure and tilth.

Weed Management Objectives

Cover crops help control weeds in spring and fall by out-competing them for resources, by not allowing a niche for them to germinate and through allelopathic compounds (See Figure 30.4). Small seeded annual weeds are controlled more than other weeds by cover crops. Cover crops do not target a single weed or family of weeds for reduction, but instead reduce the overall density of plant species.

Insect and Disease Suppression

Care must be taken when selecting species as to the efficacy of its ability to break the insect and disease cycles. Cover crops provide excellent habitats for predator insects, such as spiders and ladybugs, which like to feed on harmful insects like aphids, leafhoppers, thrips, mites, or caterpillars.

Cost of Seed and Planting

Cost and availability of seed is two practical aspects of selecting a cover crop in any vineyard operation. The amount of seed needed for good vegetative cover, the cost of that seed, and the cost establishing and maintaining the cover crop must be taken into account in choosing which cover crop to plant.

Cover Crops for Specific Purposes

The following list provides some basic information on a number of cover crops, including hardiness, biomass, weed suppression, other characteristics, and management methods.

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