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

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)

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

Root

Deep, stout taproot

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

Learn more about the author(s)

Carrie Jensen

Jennie Johnson

Heidi Kratsch

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Nevada Noxious Weed Field Guide – Diffuse knapweed