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  • Writer's pictureJen Haynes

How well do you know your knapweeds?

Knapweed is native to Europe. It is believed that knapweed came as a contaminant in alfalfa seed. Diffuse knapweed was first observed in B.C. in the early 1930s. We have four different types of knapweed in the Boundary. Spotted knapweed, diffuse knapweed, greater knapweed and Russian knapweed are classified under different management categories. Because of budget constraints, invasive plants in the Boundary are categorized under a priority management focus. In the case of greater knapweed, we only have one known site, so it is a plant that we are working to control annually with the goal being eradication. We have several Russian knapweed sites that are in the same category as greater knapweed. Spotted knapweed is under strategic control. That means that treatment is focused in high value or sensitive areas only, either for environmental, social or economic reasons. Diffuse knapweed is categorized under biological control. Many of the insects that we have for diffuse knapweed do not seem to affect the spotted in the same way. We also have hybrids of spotted and diffuse knapweed. The insects seem to do well on the diffuse and hybrid species. There are seven different bio control agents in the Boundary for knapweed. Biological control is just that, it is a control, it will not eradicate the plants. There is a cycle that you will notice with bio control. The insects feed on the plants and as there become fewer plants the insects die off. After awhile you will see an upswing in plants. As there become more plants there will be more surviving insects and the plant population will crash and the cycle will begin again. Knapweeds are extremely aggressive. They have properties that can alter the soil chemistry and that stops other plants from growing near it. When you are pulling knapweed, it is important to wear gloves. It is free to take invasive plants to the landfill in the Regional District of Kootenay Boundary, but they need to be double bagged to prevent spread. There are several herbicides that work well on knapweed. The RDKB has a loan out program if you want to borrow some equipment. They do not provide the herbicide. Reseeding after treatment helps to establish healthier plant communities by creating competition for invasive plants. Spotted and diffuse are designated as provincially noxious so if you have knapweed you are legally required to control it. If you are interested in bio control agents or finding out if they are already present on your property, please contact us. For more information please contact the Boundary Invasive Species Society at,, 250-446-2232 and on Facebook.

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