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

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

Learn more about the author(s)

Heidi Kratsch

Also of Interest:


Nevada Noxious Weed Field Guide – Diffuse knapweed Diffuse knapweed 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
Paradise Valley Weed Control Demonstration Plot: Russian Knapweed Russian knapweed is a long-lived perennial broadleaf forb. New populations typically establish from seedlings. Long-term, its spread is largely from the lateral expansion of an extensive creeping root system. Individual plants reproduce vegetatively (i.e., are clonal) and become ... Schultz, B. 2005, University of Nevada Cooperative Extension
Managing Spotted Knapweed Spotted knapweed is an invasive, noxious weed that should be prevented from invading lands in Nevada. It can be successfully managed over time using a variety of integrated measures if addressed in an aggressive, consistent manner using the best knowledge about control methods av... Graham, J. and Johnson, W. 2004, University of Nevada Cooperative Extension
Nevada Noxious Weed Field Guide – Squarrose knapweed Squarrose knapweed 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 – Russian knapweed Russian knapweed 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 – Spotted knapweed