Weed of the Week – Canada Thistle

Invasive plants are non-native and cause damage to the environment, economy and our health. They grow rapidly and spread quickly. Invasive plants are the second greatest threat to biodiversity after habitat loss.

May is Invasive Species Awareness Month, and the Sea to Sky Invasive Species Council, a local environmental non-profit, is using this opportunity to showcase invaders that are found around Pemberton and the area. Be on the lookout for these invaders!

canada thistle

Canada Thistle

Don’t let its name fool you, Canada Thistle actually came from the Eastern Mediterranean region! It was likely one of the first weeds imported to North America by early settles. Its flower heads are white to purple, about 1cm in diameter, borne on clusters of 1-5. The flowers bloom from June to October, and have a sweet vanilla smell.

Canada Thistle can be differentiated from all similar species by the lack of spines on the main stem, small flowers, and height (less than 2m tall).

Canada Thistle plants crowd out forage grasses in pasture and rangelands, reducing yields and productivity. More generally, invasive plants’ agricultural impacts include crop losses, increased maintenance costs, reduced product quality and quantity, human and health concerns (from mild allergies to poisonings), and lowered land values. Pemberton farmers depend on their land to make a living and provide food for the community. Weeds don’t respect fence lines, and in order to manage them effectively, all neighbours need to work together to stop the spread.

How to remove it: Mowing is most effective when completed at the bud stage. Regular cutting or tillage can help wear down plant reserves, reduce plant growth, and reduce populations, but is not likely to kill the plant. Care should be taken to ensure that plant parts are not distributed during transport.

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