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scourge of the West!

Last Update : 8/10/96
Diffuse Knapweed, or Centaurea diffusa is threatening our pastures and is toxic to horses. We have an image, followed by a description and more information...


The problem...

Diffuse knapweed is affecting the county's ecology by invading dry, disturbed areas such as roads, trails, and over-grazed pastures. Once established, it forms dense stands, crowding out native plant species. It can seriously affect the productive potenti al of rangelands and is toxiic to horses.

The culprit...

There are three types of knapweed: diffuse, spotted, and Russian. About 90% of the knapweed found in Boulder County is the diffuse type, Centaurea diffusa. The plant grows like a thistle with an elongated tap root. It reproduces and spreads from se eds. Knapweed developes a single main stem that grows 1 to 2 feet tall. The leaves are grayish-green and covered with tiny hairs. They become smaller towards the top of the shoot and have smooth margins. Flowers - Numerous solitary flower heads occ ur on short tips. The flower heads are usually white in color but may be purplish. Seed head bracts end as sharp rigid spines which can penetrate skin easily.....watch out! The plant is similiar to tumbleweeds in that they fracture at the base and tumble or blow.


By hand -
Rainbow Valley has started a campaign called "WHACK THE KNAP ATTACK!" Volunteers patrol throughout the county, looking for stands of Knapweed that are accessible to hiking and biking trails. When such a stand is located, a re-cyclab le sign is posted, identifying the problem and asking that users of the area pull a few...and help prevent the unecessary use of pesticides.
This program will be assessed for effectiveness, and potentially be renewed earlier next year.
Herbicides -
Noxious Weeds, why we need to control them.
Colorado State Co-operative Extension Publications are a good place to look for information, this link is to Natural Resources Publication on Weeds
Biological controls -
The Colorado Department of Agriculture, Division of Plant Industry, Biological Pest Control Division has put out information on the Spotted and Diffuse Knapweed Biological Control Plan. A half dozen different beetles, weevils, moths and flies are natu ral enemies of Knapweed, and most are extremely specific.
More information can be attained by contacting:

Div. of Plant Industry, CDA
700 Kipling St., Suite 4000
Lakewood, CO 80215
(303) 239-4140

*Information about these techniques is currently being researched for accuracy....If you have immediate questions, please contact Rainbow Valley.

General Weed Information

Internet Weed Resources
Saskatchewan Weed Information

Colorado Weed Management Association

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