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  
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
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
African mustard plant
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
Photo of common crupina stem
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
Photo of Common St. Johnswort plant
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
 

Associated Programs

Master Gardeners at tabling event

Master Gardeners of Nevada

Program trains local gardeners to provide research-based horticulture information to Nevadans

ladybug larva eating aphids on a pepper plant

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.

master gardeners in garden

Master Gardeners of Washoe County

Master Gardeners provide free, research-based horticulture information to Nevadans.