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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

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

Learn more about the author(s)

Heidi Kratsch

Also of Interest:


*Needs Assessment for Noxious Weeds in Churchill County: Part 4 of 5 - Criteria for Herbicide Use and Selection* This fact sheet is the fourth in a series of five that reports the results of a needs assessment survey completed by faculty in University of Nevada Cooperative Extension (UNCE). The survey attempted to identify the major issues related to the management and control of weeds in N... Davison, J., Powell, P., Schultz, B., and Singletary, L. 2012, University of Nevada Cooperative Extension
*Nevada’s Priority Agricultural Weeds: Hoary Cress* Plants commonly referred to as hoary cress (Cardaria sp.), or short whitetop, are one of three different but closely related perennial forbs. The Cardaria species are widespread across all eleven Western states, including every county in Nevada. B. Schultz, S. Foster 2021, Extension, University of Nevada, Reno, SP-21-03
*Nevada Noxious Weed Field Guide – African mustard* African mustard 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., H. Kratsch, Moe, A., Schultz, B. 2020, Extension, University of Nevada, Reno, Field Guide
*Nevada Noxious Weed Field Guide – Common crupina* Common crupina 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 – Common St. Johnswort* Common St. Johnswort 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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Master Gardeners of Nevada

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Nevada Noxious Weed Field Guide – Diffuse knapweed