Diffuse knapweed
Centaurea diffusa

• Diffuse knapweed is a native of Eurasia that has been known to exist in the U.S. for at least 80 years. Prior to 1977, infestation in Idaho were primarily in the southern part of the state. Recently, it has spread to other areas. In the past, this weed infested dry rangeland, rights-of-way, waste areas, and similar sites. Diffuse knapweed has invaded forested areas, which may indicate it is adapting to areas with higher precipitation.
• Diffuse knapweed is on the Idaho noxious weed list.
• Diffuse knapweed is an annual, biennial or short-lived perennial that can grow to a height of 3 feet, with a many-branched stem that usually has a bush appearance. Tips of each branch have a white or sometimes pinkish flower head. Bracts surrounding the flower are yellowish-green with a light brown margin. The upper part of each bract narrows into a short, stiff spine.
• Biological agents are available to aid in management of this and other knapweeds.

Report Sightings of Noxious Weeds

Contact:
Kim Pierson, USFS Botanist
208-737-3212
kpierson@fs.fed.us

SPREAD THE WORD ... NOT THE WEEDS

• Drive only on established roads and trails away from weed infested areas.
• When using pack animals, carry only feed that is certified weed free.
• Removed weed seeds from pack animals.
• Don't pick the flowers of noxious weeds and take them home.
• Don't pick and transport wild flowers that you can't identify.
• Don't camp or drive in weed infested areas.

Weed Removal Instructions

No Flowers or Seed Present:
Pull the weed and leave it on the area.

Flowers or seed present on the weed:
Pull the weed. Be careful the seed does not fall from the weed. Place the weed in a plastic bag or similar container.

Dispose of the weed by burning or turn it in at a Ranger Station.