Weed and Vegetation Management

Floor management practices have significant effects on vineyard growth and vigor, and more so in young vineyards. If left uncontrolled, weeds can reduce new vine biomass by more than 80%. Weed control also helps to conserve soil moisture for the grapevines.

Vegetation management in vineyards is determined by site-specific environmental factors. Weed competition and interference must be minimized within the row while trafficability and soil conservation are required between rows (see "Section L. Vegetation Management in Orchards, Vineyards, and Berries" in this handbook). The choice of floor management practices will differ for the area between the rows or "alleyways" and the area under the vines. Conventionally, alleyways are kept with resident vegetation that is mowed or cultivated.

Cultivation Tillage controls annual weeds and suppresses perennial weeds. Cultivation is required every 3 weeks for 2 years or more to eventually deplete perennials. Soil temperatures are increased by tillage or cultivation that keeps the soil surface bare, especially during grape maturation west of the Cascades. Growers often compromise by tilling every other row in alternate years to ensure trafficability during harvest. Adverse effects of tillage include soil erosion from sloping sites, soil compaction, and reduced water infiltration during winter rains (except in very sandy soils).

Under-vine Weed Control: Several types of equipment exist with varying degrees of soil disturbance. On the high soil disturbance spectrum there are French plows, grape hoes, and rotary tillers. On the low soil disturbance spectrum there are rotary brushes, finger weeders, and under-vine mowers. No one piece of equipment will provide complete control of weeds, and some are designed to be used in tandem. Other unique types of equipment available for under-vine weed control include pressurized water systems (e.g. Acqua knife), flamers, and saturated steam applicators (e.g. Weedtechnics), but this equipment is not commonly used in vineyards in the PNW.

The selection of which equipment to use is complex, but a few aspects worthy of consideration are the availability of technical support to ensure replacement parts are available, the required tractor power and hydraulic output in case multiple units are being used, and ease of operation as certain equipment may require a more skilled operator.

Flame weeding Propane burning will sear small broadleaf weeds, but will only reduce vegetative growth of grasses and perennial weeds since growing points remain protected beneath the soil surface. Metal shrouds or covers conserve fuel by briefly elevating temperatures.

Herbicides Grape roots proliferate in undisturbed, competition-free strips representing one-third to half of the planting area, depending on moisture availability. New plantings require supplemental water or nearly vegetation-free conditions during the first 3 years of establishment. Choose combinations of practices that act together to achieve your desired level of vegetation management.

Managing herbicide resistance Dependence on glyphosate in vineyards is exerting strong selection pressures on weed populations and may ultimately lead to weeds that are resistant to glyphosate. Several alternative, nonselective herbicides, listed below, have different sites of action and can be applied in rotation with glyphosate to reduce the risk of selecting for weeds that are resistant to glyphosate. Refer to "Section C. Agrichemicals and Their Properties" and the subsection "Managing Herbicide-Resistant Weeds" in this handbook for more information.

Steps to avoid or manage glyphosate resistance

  1. Use other means to manage weeds, such as cultivation, mowing, and flailing.
  2. Use preemergence herbicides where possible. Consider use of other nonselective herbicides, such as glufosinate or paraquat with PPO inhibitors for burndown control.
  3. To delay development of resistance, use the full, labeled rate of glyphosate.
  4. If continuing to use glyphosate in orchards or vineyards with resistant weeds, then tank mix glyphosate with other herbicides and make the application when the weeds are small.
  5. Do not let weeds go to seed. In the case of weeds that outcross, do not let weeds produce pollen.

Mowing or flailing Mowing or flailing grass sods or weedy vegetation in aisles improves trafficability, prevents erosion, and improves soil conditions. Improved turf grass varieties, combined with water and fertilizer management for both the crop and sod, offer long-term advantages in soil management. However, caution is advised during vineyard establishment under nonirrigated conditions where vine growth may be reduced in the first 3 years from competition by most deep-rooted vegetation.

Mulches Organic mulches suppress weeds, conserve moisture, and improve soil tilth. Most polyethylene films last only one or two seasons. Woven or spun-bonded fabrics have controlled weeds for 5 to 7 years if the surface remains free of mulch or leaf debris that encourages weed germination.