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

Stem

  • Up to 2 ft. tall; rough-textured; highly branched; bushy; covered with short, stiff hairs; NO wings on upper stems 
Photo of diffuse knapweed stem
 

Leaves

  • Alternate, lower leaves pinnate-divided, 4-8 in. long; sometimes covered with short grayish hairs; upper leaves strap-like (linear) with smooth edges (margins)  
Photo of diffuse knapweed seedling
 

Flower

  • White to pale purple, located at the tip of a branch; base of flower is vase-shaped, 0.5 in. long, 0.12 in. wide and covered with yellow, comb-like bracts tipped with a narrow spine 
Photo of diffuse knapweed flowers
 

Root

  • Deep, stout taproot
Photo of diffuse knapweed
 

Other

  • Grows best in dry, well-drained soils; often infests rangelands, waste areas and roadsides; known to occur in Douglas, Elko, Eureka, Lander, Lincoln, Nye, Washoe and White Pine counties
  • Biennial, but sometimes annual or perennial; reproduces by seed; dry, mature plants often break off and tumble in the wind to spread seed
Photo of diffuse knapweed with white and pink flowers
 

Control

  • Mowing plants in bud to flower stage can reduce seed production; repeated hand removal can be effective; burning is NOT effective
  • Several insect biological control agents are available
  • Apply 2,4-D or dicamba in the rosette stage; apply aminocyclopyrachlor, aminopyralid, chlorsulfuron, clopyralid, imazapyr or picloram pre-emergence to rosette and mid-bolt stages  

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