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Posted: July 31, 2019

Tackling spreading invasive knapweed along Columbia Lake

Knapweed is spreading along Columbia LakeÔÇÖs shore, and it is affecting the shoreline stability and plant diversity.

On July14, 10 volunteers from the Columbia Lake Stewardship Society and the East Kootenay Invasive Species Council pulled and removed 17 large garbage bags of knapweed from approximately 400m of shoreline. More remains to be done.

Spotted and Diffuse knapweed are non-native plants considered regionally noxious under the BC Weed Control Act. Spotted knapweed is more common and can produce up to 140,000 seeds per square meter, whereas diffuse knapweed is less common and produces up to 18,000 seeds per square meter. Both plants are spread by vehicles (trains), wind, livestock and people. These plants are a problem because they choke out desirable forage for livestock and wildlife and cause increased soil erosion.

Identification: Biennial to short-lived perennials growing up to 1 metre in height, with taproots.

Diffuse (pictured right): hairy, greyish green, split leaves. The flowers are white or sometimes purple with small, sharp rigid spines on the bracts.

Spotted (pictured left: hairy, deeply-cut leaves and purple flowers.

If you come across these plants, carefully pull them out from the base in order to fully remove the root. Dispose of them in a sealed plastic bag.

Diffuse knapweed (source:

Spotted knapweed (source:

Columbia Lake Stewardship Society

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