Stem

  • Up to 4 ft. tall, rough-textured, branched and bushy; NO wings on upper stems
Photo of spotted knapweed stem with leaves

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
Photo of spotted knapweed plant

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)
Photo of spotted knapweed pink flower

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

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Also of Interest:

 
Photo of diffuse knapweed with white and pink flowers
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
Russian Knapweed Control Trial 2013-2015, Pershing County
A document of effective ways to maintain and control Russian Knapweed crops.
Foster, S., and Schultz, B. 2016, Extension, University of Nevada, Reno, PS-16-04
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
Photo of squarrose knapweed plant with small pink flowers
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
 

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Integrated Pest Management

Integrated Pest Management program is a long-term management strategy that uses a combination of tactics to reduce pests to tolerable levels with potentially lower costs for the pest manager and minimal effect on the environment.