Fraser Valley Invasive Plant Council

Weed Management Strategies

Manual/Mechanical Control:

  • Tillage/cultivation
  • Hand weeding or pulling
  • Mowing or cutting
  • Excavation (for example in the case of species like Himalayan blackberry or reed canarygrass)

Cultural Control

  • Crop rotation
  • Competition

Biological Control

Biological control is one of the more interesting management strategies for invasive plants. Biological control agents are organisms (usually insects) that can be used to reduce weed populations. These agents are usually the natural enemies of weeds in their native environments.

It takes decades for a biocontrol agent to be approved and released into the wild. Before introduction of a natural agent to Canada is approved, Canadian and United States scientists review exhaustive long-term studies to ensure safety. In order to be released in North America the agent must damage only the target weed and not transfer to any other plants.
Biological control is best suited to large, dense infestations where other management strategies are neither cost-effective nor environmentally desirable. It is intended to weaken the target weed by decreasing seed production and reducing weed density – not to eradicate the weed species.
In the Fraser Valley the following weed species are under biological control:

  • Purple loosestrife
  • Canada and bull thistle
  • Spotted knapweed
  • Tansy ragwort
  • St. John's wort
  • Hound's tongue

Chemical Control (Herbicides)

Herbicides are chemicals designed to kill or injure plants. In the Fraser Valley we use a combination of manual and chemical control on Japanese knotweed, scotch broom, and butterfly bush. Herbicide use is localized to the invasive plant and measures are taken to protect native vegetation. Crews use backpack spray, stem injection, cut and fill, or cut and paint techniques. All chemical control work is completed by certified pesticide applicators and follow protocols outlined in the Pest Management Plant for the South Coast (download pdf) which also has a very informative Backgrounder (download pdf)