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Report an Invasive Species

How We Control Invasive Plants

Invasive Plant Management Steps

  1. Map the entire management area and its resources
  2. Map and inventory invasive plants within the management area (use the Invasive Alien Plant Program, a public database where all invasive plant inventory and treatment data is housed)
  3. Set invasive plant management goals, objectives, and priorities
  4. Select and implement invasive plant management strategies (manual/mechanical, chemical, biological control – usually some combination of multiple methods)
  5. Develop a monitoring program


Management Strategies

Integrated Pest Management (IPM) is a decision-making process that includes identification and inventory of invasive plant populations, assessment of the risks that they pose, development of well-informed control options that may include a number of methods, site treatment, and monitoring. There are four primary control options (besides prevention) for the management of invasive plants: cultural control, mechanical control, biological control, and chemical control.


Prevention is the best method of controlling the introduction and spread of invasive plants.

  • Learn to identify and control invasive plants using methods suitable to site and species
  • Know what you grow - avoid growing invasive plant species; substitute invasive plants for less aggressive species
  • Remove plants that are creeping or reseeding outside of their intended area
  • Revegetate disturbed areas with regionally appropriate (i.e., native), non-invasive, non-persistent seed mixtures or plants
  • Do not dump plants or plant material over the back garden fence or into greenspace
  • Clean equipment, tools, vehicles, pets, and shoes before leaving an infested area
  • Do not compost invasive plants

Cultural Control:

  • Plant native or non-invasive plants that will outcompete or shade out invasive plants

Manual/Mechanical Control:

  • Tillage/cultivation
  • Hand weeding or pulling
  • Mowing or cutting
  • Excavation (for large scale areas)

Biological Control:

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
  • Dalmatian toadflax

Chemical Control:

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, 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 Plan for the South Coast.