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

Stem

Up to 4 ft. tall, rough-textured, branched and bushy; NO wings on upper stems

Leaves

Alternate, gray-green, up to 8 in. long; most are pinnate-divided, dotted with resin and sometimes covered with small grayish hairs; upper leaves smaller and narrower with few to no lobes

Flower

White to purple, each located at the tip of a branch; base of flower is vase-shaped, 0.5 in. long, 0.3-0.5 in. wide and covered with bracts with dark, comb-like tips that give the appearance of spots (after which the weed is named)

Root

Deep, stout taproot

Photo of spotted knapweed plant in a field of dry grass

Other

Grows best on dry, well-drained soils; often infests rangelands, waste areas and roadsides; known to occur throughout Nevada
Biennial; reproduces by seed and lateral roots

Photo of a field with spotted knapweed plants

Control

Mowing plants in bud to flower stage can reduce seed production; repeated hand removal can be effective; DO NOT burn
Several insect biological control agents are available
Apply 2,4-D or glyphosate rosette to bolt stage; aminocyclopyrachlor, aminopyralid, clopyralid, or picloram preemergence to bolt stage

Learn more about the author(s)

Heidi Kratsch

Also of Interest:

Nevada Noxious Weed Field Guide – Spotted knapweed