Weeds

Invasive plants are a serious threat to B.C.'s agricultural industries and natural resources.

The Invasive Species Council of BC defines the term "invasive plant" as any invasive alien plant species that has the potential to pose undesirable or detrimental impacts on humans, animals or ecosystems. Invasive plants have the capacity to establish quickly and easily on both disturbed and undisturbed sites and can cause widespread negative economic, social and environmental impacts.

Many invasive plants have been introduced to B.C. without the natural predators and pathogens that would otherwise keep their populations in check in their countries of origin.

Impacts associated with the introduction and spread of invasive plants affect all agricultural industries in B.C. These unwanted invaders can negatively impact:

  • Agriculture — by reducing crop yield and quality and increasing management costs
  • Rangelands — by reducing forage quality and quantity
  • Forestry operations — by competing with seedlings for light, nutrients and water
  • Recreation opportunities — by puncturing tires, obstructing trails and reducing aesthetics
  • Water quality and quantity — by increasing erosion and sedimentation

Invasive plants also threaten protected areas, wildlife, property values, public health and safety and the ecological health and diversity of the province’s natural environment.

Invasive species are the second largest threat to our biodiversity, after direct loss of habitat.

The Weed Control Regulation of the B.C. Weed Control Act designates 66 plant species as noxious weeds, with 39 of those being identified as provincial weeds and 27 classified as noxious within the boundaries of specific regional districts. All of these species are non-native plants that create problems in agriculture and/or natural habitats.

The majority of invasive plant species and about two-thirds of pests established in or threatening B.C. are species from outside North America.

Invasive alien plants affecting or potentially affecting grapes in B.C.

Plant Distribution Suspected year of introduction Registered control products?
Puncturevine (Tribulus terrestris) Predominately Penticton, south into the Okanagan and Similkameen valleys expanding north 1970s Yes
Leafy Spurge (Euphorbia esula) North Okanagan, with potential to move to South Okanagan 1970s Yes
Rush Skeletonweed (Chondrilla juncea) North Okanagan Valley, with potential to move to South Okanagan 1990 Yes
Perennial Pepperweed (Lepidium latifolium) West Thompson region near Walachin and Windermere Lake, East Kootenays 1992 Yes
Field Scabious (Knautia arvensis) Boundary region, Thompson region 1990 Yes
Common Bugloss (Anchusa officinale) Central Okanagan Valley, East Kelowna area, Rock Creek 1990 Yes
Longspine sandbur (Cenchrus longispinus) South Okanagan Valley 1990s Yes
Wild-Four O’Clock (Mirabilis nyctaginea) South Okanagan, Osoyoos area 1970s Yes

 

For information on identification of noxious weeds, download the province's Field Guide to Noxious Weeds and Other Selected Invasive Plants of British Columbia, Twelfth Edition 2023 (PDF).

Management

Selection and management of appropriate ground cover vegetation will assist in managing weeds. For information on managing vineyard cover crops, see Vineyard Floor Management.

The elimination of all vegetation around young grape vines is essential to eliminate competition and promote satisfactory growth that will result in early commercial yields. Newly planted grape vines are poor competitors for moisture and nutrients. Heavy sod will cause severe stunting of young vines.

Physical control

Effective weed control is possible by plowing, disking and clean cultivation or by establishing a competitive cover crop a year before planting. Excessive mechanical cultivation destroys soil organic matter and leads to a breakdown in soil structure.

Effective weed control under the trellis is possible with mulch and a hand or mechanical grape hoe. Hand weeding may be practical for small vineyards if perennial weeds are eliminated the year before planting. Hand weeding frequently leads to disaster if it is not done on a routine, daily basis.

Effective weed control, using mechanical means, requires repeat operations that can be labour intensive, destroy organic matter, reduce water penetration and lead to trunk or root injury.

Mulches

Mulches consisting of a variety of materials can be used to control weeds and moisture.

Sawdust or wood shavings can be used, but avoid cedar products. Grass clippings or hay could also be used, but these products contain seeds that may germinate.

Fertilizer applications may have to compensate at a later date for the use of nitrogen by soil organisms to break down the organic matter in the mulch.

To be effective against annual weeds, organic materials must be at least 15 cm thick around the vine and in the area where weeds must be controlled.

Control of perennial weeds should be done before planting since these are not easily controlled by organic mulches.

Chemical control

Be cautious and accurate when using herbicides. Use proper equipment maintained in good condition and calibrated accurately. Visit the Pesticides page for more information. Safe and effective chemical weed control measures are widely used.

  • Successful chemical weed control always depends on the proper application of the correct amount of recommended herbicides.
  • Soil organic matter strongly influences the activity and safety of residual chemicals.
  • Repeated yearly applications with residual herbicides may result in build-up of these chemicals in the soil and cause plant damage.
  • Do not apply herbicides to vineyards when the soil is frozen.

Serious injury to grape vines can occur if the land that is to be planted to vineyard has been treated with residual herbicides. Such land can be tested for herbicide residue the year before grapes are to be planted by growing cucumbers in a soil sample. Normal germination and growth of this indicates that the area is safe for grape growing.