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...
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.
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.
*Information about these techniques
is currently being researched for accuracy....If you have immediate questions,
please contact Rainbow Valley.
- By hand -
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 -
Weeds, why we need to control them.
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
700 Kipling St., Suite 4000
Lakewood, CO 80215
Weed Management Association
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