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

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

Extension Associated Contacts

Heidi Kratsch

Also of Interest:


Insect Management Applying IPM strategies: Insect control can be split into these five separate categories. Hefner, M. 2019, Extension, University of Nevada, Reno
What Are Those Weird Bumps on My Fruit Tree? Understanding Kuno Scale Kuno scale is a common soft scale insect that often appears as small bumps on ornamental plum trees. This blog explains how to identify Kuno scale, understand its life cycle, recognize damage symptoms, and choose effective, timely management options. Andrews, M. 2026, University of Nevada, Reno Extension, Blog
What Should Gardeners Know About Ladybug Releases? The Pros and Cons A clear, balanced look at the pros and cons of releasing ladybugs for pest control. Learn why most bought ladybugs fly away, the ecological risks many gardeners overlook, and smarter, more sustainable ways to support beneficial insects in your garden. Jensen, C. 2026, University of Nevada, Reno Extension, Blogs
How to Identify Pests Using Your Phone When dealing with a pest problem, one of the first challenges is figuring out exactly what you’re up against. Many mobile apps and online tools allow you to take or upload a photo to get possible identifications. Jensen, C.; Johnson, J. 2025, Extension, University of Nevada, Reno, Blog
Winter Bird-Friendly Garden Tips Some tips for providing habitat for birds during the winter months. Creating a bird-friendly garden is a good way to provide wildlife habitat in urban and suburban areas. Plus, birds help keep lots of garden pests in check. Jensen, C. 2024, Extension, University of Nevada, Reno

Associated Programs

Master Gardeners of Nevada

Program trains local gardeners to provide research-based horticulture information to Nevadans.

Master Gardeners of Washoe County

Master Gardeners provide free, research-based horticulture information to Nevadans.

Garden plant and pest sprayers image by Olga Seifutdinova from Getty Images

Integrated Pest Management

Integrated Pest Management (IPM) is a strategy that reduces pests to tolerable levels with lower costs for the pest manager or home gardener and minimal effect on the environment. The IPM program at University of Nevada, Reno Extension focuses on identification and public education with resources for the community including classes, Spanish language resources and a pest directory.

Nevada Noxious Weed Field Guide – Canada thistle