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

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Nevada Noxious Weed Field Guide – Malta starthistle Malta starthistle is a noxious weed that has been identified by the state of Nevada to be harmful to agriculture, the general public, or the environment. Learn more about this weed. Blecker, L., Creech, E., Dick, J., Gephart, S., Hefner, M., Kratsch, H., Moe, A., Schultz, B. 2020, Extension, University of Nevada, Reno, Field Guide
Nevada Noxious Weed Field Guide – Perennial sowthistle Perennial sowthistle is a noxious weed that has been identified by the state of Nevada to be harmful to agriculture, the general public, or the environment. Learn more about this weed. Blecker, L., Creech, E., Dick, J., Gephart, S., Hefner, M., Kratsch, H., Moe, A., Schultz, B. 2020, Extension, University of Nevada, Reno, Field Guide
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Nevada Noxious Weed Field Guide – Yellow starthistle Yellow starthistle is a noxious weed that has been identified by the state of Nevada to be harmful to agriculture, the general public, or the environment. Learn more about this weed. Blecker, L., Creech, E., Dick, J., Gephart, S., Hefner, M., Kratsch, H., Moe, A., Schultz, B. 2020, Extension, University of Nevada, Reno, Field Guide

Nevada Noxious Weed Field Guide – Spotted knapweed