Introduction
The RVF believes that herbicides are negative for soil health, and the goal of a fully regenerative system in vineyards should be to work towards establishing a system where herbicides are no longer used.
However, transitioning from a system that relies on herbicide use can take a long time, and on balance, the use of herbicide to control persistent and troublesome undervine weeds may well be less damaging to the soil than regular soil disturbance.
Using other physical methods to control weeds (ideally ones that minimize any disturbance to the soil) should always be the preference, but vineyard managers will need to make a judgment about what balance of management techniques they should use in each of their vineyards at the point they have reached in their transition.
In detail
For many decades it has been common practice in many viticulture regions to have bare earth both interrow and undervine. Systemic herbicides were routinely used to kill the ‘weeds’ as it was thought these plants outcompeted vines for water and nutrients.
Glyphosate is the most widely used herbicide, thought for a long time to be relatively benign due to claims of ‘low persistence’, i.e. it doesn’t stay around for very long. It works by targeting a chemical reaction in plants that stops them functioning. However, it also ‘chelates’ (grabs) molecules including calcium, manganese, copper and zinc. When it is applied, some of the droplets go directly onto the soil, some of the glyphosate is released into the soil via plant root exudates and residues are released into the soil when the plants die and break down. Therefore soil nutrient availability is affected by glyphosate chelation of micronutrients.
It is known that herbicides can:
- damage soil health and earthworm ecology
- interfere with nutrient uptake
- remove living roots from the soil, affecting soil structure and causing soil compaction and water and nutrient run off
- have a large carbon footprint associated with its manufacture
- lead to resistant ‘weeds’, that are very difficult to get rid of, with low diversity
It is also thought that that the chelation of manganese affects the vine’s resilience to disease. Manganese is key to plant defence.
There is also concern that it is potentially carcinogenic to workers.
In some vine growing regions the use of glyphosate is being prohibited. However, this introduces the risk that growers will resort to more damaging herbicides which have not yet been prohibited.
What is the alternative?
In some geographies/viticulture regions there has been a significant shift to allowing plants to grow in the interrow areas of vineyards. This has been encouraged by the knowledge that suitable plants can bring so many other benefits to the soils, vineyard and surrounding ecology and vine health. Management of plant growth in the interrow areas of vineyards is relatively easily achievable (see Interrow Tillage section).
However, managing plant growth undervine remains a more challenging area from both a technical and a viticultural perspective, because unmanaged undervine plant growth can lead to negative nutrient and water competition, and increase humidity within the productive vine space, which in turn can increase disease pressure. The most appropriate method of managing the undervine area is always context specific. Preferred options in the RV toolkit include:
- Allowing plants to exist undervine and managing them by mowing or strimming: this is regarded as the most environmentally sustainable practice if your vineyard context allows it
- Applications of mulches or fleece to act as weed suppressants
- Allowing animals such as chickens to ‘scratch’ plants in the undervine area
Shallow cultivation to remove plant growth around the base of the vines (using an interceptor bar to avoid damaging the vine) is better than tillage which inverts the soil. However, it can still release carbon into the atmosphere, damage microbial networks around the vine and its roots (depending on cultivation depth), decrease vineyard biodiversity, and can be energy intensive if undertaken as a separate vineyard task.
Different vineyard life stages can result in different decision making. Using herbicides during the first few years of establishment is still widely practised, while the plants establish their roots. Some regenerative viticulture practitioners have demonstrated that it is possible to plant directly into existing sward, but evidence is still being built on its effect.
One block trial If you are using herbicide to manage plant growth undervine, please consider trialling a different method in one row or block of your vineyard, perhaps allowing plants to grow, which you then mow or strim, or shallow cultivate with a finger weeder or similar. Take lots of measurements, compare disease pressure, soil health, yields, grape quality, costs over a few years and observe the results.