Canadian Thistle

Genus: Cirsium

Species: arvense

Description: Over 1 meter (3 ft) in height, leaves are dark green and prickly with a hairy underside, flowers are purple to white.

Where it grows: Found in open, disturbed areas such as agricultural land and roadsides.

How it spreads: Spreads through root dispersal and seeds spread by wind and water runoff, can generate from fragments as small as 5 cm (2 in).

What it threatens: Competes with crops for moisture, nutrients and light. Harbors destructive insects and pathogens.

More information: Nature Conservancy website

Disclaimer - Clean Water Services does not endorse or recommend specific herbicides for use in controlling these species. To protect water quality, always follow herbicide label directions and obey application laws when using any herbicide.