Blecker, L., Creech, E., Dick, J., Gephart, S., Hefner, M., Kratsch, H., Moe, A., Schultz, B. 2020, Nevada Noxious Weed Field Guide – Canada thistle, Extension, University of Nevada, Reno, Field Guide

Stem

Up to 4 ft. tall, green to brown, branched at the top and usually lacks hair (glabrous)

Leaves

Alternate, oblong or lance-shaped, 2-8 in. long, shiny and lack hair; NO leaf stems (petioles); leaf edges (margins) are wavy, lobed or toothed with spiny edges

Canada thistle rosette

Flower

Pink, purple or white; occur in clusters at the ends of branches; base of flower is vase-shaped, 0.5-0.75 in. wide, lacks prickles and is covered with green to purple bracts with dark tips

Canada thistle flowers

Root

Deep, extensive creeping root system

Other

Grows best in moist areas; often found in pastures, hay fields, waste areas and along waterways; known to occur throughout Nevada
Perennial; reproduces by both roots and seed; plants often appear in patches or colonies due to the spreading root system

Control

Repeated mowing, tillage, cutting or hand removal prior to seed production can provide suppression
Several biological control agents are available
Apply aminocycloprachlor, aminopyralid, chlorsulfuron, clopyralid or picloram pre- or post emergence; repeated applications of 2,4-D, dicamba or glyphosate to actively growing plants

Learn more about the author(s)

Heidi Kratsch

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Nevada Noxious Weed Field Guide – Canada thistle