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

Stem

Up to 12 ft. tall and branched, with spiny wings along smooth stem; covered with wooly, gray hairs

Leaves

Alternate; oblong, 4-20 in. long, covered with wooly, gray hairs giving plant a gray-green appearance; edges (margins) are lobed or toothed with stiff spines

Flower

White to purple flowers, each located at the tip of a branch; base of flower is round and resembles a squashed globe, 1-2 in. wide and covered with green, purple or yellow bracts less than 0.2 in. long, each tipped with a spine; often covered with wooly, gray hairs

Root

Fleshy taproot

Other

Often infests pastures, rangeland, roadsides and waste areas; known to occur throughout Nevada
Biennial; reproduces by seed
Forms dense stands that are difficult for humans and animals to penetrate

Control

Hand-removal, digging or mowing prior to flowering can be effective
Apply 2,4-D, chlorsulfuron, dicamba, metsulfuron or picloram to actively growing rosettes; aminopyralid, chlorsulfuron, clopyralid or dicamba+2,4-D between rosette and late-bolt stage; aminocyclopyrachlor pre- and post emergence

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Nevada Noxious Weed Field Guide – Scotch thistle