The Australian Wine Research Institute

Background

Mid-row cover crops (permanent swards and annual cover crops) are commonly used in vineyards to improve soil health and manage weeds. More recently, researchers and growers have started to trial cover crops as a way to control weeds undervine. In suitable environments, the correct species of cover crop can effectively suppress the growth of other plants.

Figure 1. Ryegrass undervine cover crop suppressing kikuyu in a McLaren Vale vineyard (courtesy of Troy Elliker, Gemtree)

Action

Actively growing cover crops compete with weeds for water and nutrients. Cover crops also suppress weed seed germination by blocking sunlight from reaching the soil surface (Figures 1 and 2). Some cover crop species, such as barley and cereal rye, produce allelochemicals which suppress weed growth (Figure 1).

Cover crop residues remaining after senescence suppress weeds during summer when retained as a surface mulch. Mid-row cover crop residues can also provide some weed control when mown and thrown undervine.

Figure 2. Undervine clover in the Barossa (image courtesy of Karl Schiller)

Advantages and disadvantages

Advantages: In addition to weed control, cover crop species or mixes of species can be sown to provide a variety of benefits. For example:

• Leguminous species such as faba beans, field peas, vetches, lupins, clovers subclovers and medics fix nitrogen in the soil. A legume crop can add 100 kg of nitrogen per hectare of cover crop when incorporated into the soil.
• Flowering species such as alyssum, phaselium, buckwheat, wallaby grass, windmill grass, Queensland bluegrass, creeping saltbush and ruby saltbush attract beneficial insects.
• Species of brassica and legumes with deep taproots, such as fodder radish, faba beans and lupins, are good at breaking up hard pans and heavy soils.
• Cereals and grasses with fibrous root systems, such as cereal rye, triticale, annual rye grass, perennial rye grass and tall fescue, improve soil structure, soil organic carbon levels, water infiltration rates and reduce soil erosion.
• Generally, the use of cover crops results in an increase in soil microbial diversity, soil microbial biomass and activity in soil top layers (0-5 cm) and earthworm numbers compared to managing weeds with herbicides or cultivation (Abad et al. 2021).
• Cover crops can also provide better access to the vineyard following rain or irrigation and may increase humidity and reduce vineyard floor temperatures.
• Cereal rye, triticale, oats, barley, fodder radish, oilseed mustard, established wallaby grass and creeping saltbush are all good weed competitors when managed appropriately (Nicholas et al. 2004).

Disadvantages:

• For undervine cover crops, significant site preparation and modified seeders may be required for good crop establishment.
• Permanent undervine cover crops may need to be resown every few years to maintain dominance over weeds.
• Perennial swards and annual grasses such as perennial ryegrass, tall fescue, cocksfoot, lucerne, chicory and annual ryegrass can all compete heavily with vines if not managed effectively, leading to reduced yields.

Table 1. Performance of undervine cover crops in achieving different outcomes

Note: environmental influences on cover crop performance will affect their weed suppression.

Considerations

Cover crops vary widely in their characteristics and a range of factors must be considered when choosing species, especially for the undervine area. These include:

• selection of short-season annual grass and legume species which complement the vines’ water and nutrient requirements
• irrigation rate
• availability of tillage, seeding and mowing equipment
• the risk of fire and/or frost.

Table 2. Ease of establishing undervine cover crops on different soil types