BMNRI Home > Publications
> Weeds > Diffuse
Publications: Noxious Weeds
in Slow Motion: A
talk by Jerry Asher about noxious weeds in the Blue Mountains
Click on a weed to learn about how to find it and kill it!
Alias: Tumble knapweed, bushy knapweed
- Stem: Single with many branches, gives plant a bushy
look. Up to 4 feet tall.
- Leaves: Grayish-green. Lower leaves divided several times,
uppers once divided into narrow segments. Leaves are 6 inches
long at the base, they get smaller further up the stem.
- Heads: Numerous, narrow, few-flowered.
- Flowers: Numerous, white to rose, sometimes purplish.
Flowering period is from July to September.
- Bracts: Are yellowish-green with a light brown comb-like
- Fruits: Brown or grayish with several longitudinal stripes
and usually without a terminal tuft of hair.
Diffuse knapweed infests roadsides, waste areas, and dry rangelands,
and spreads into new areas quite rapidly. It forms dense stands
and excludes more desirable forage species. It spreads by seeds,
which are scattered by windblown tumbling mature plants.
***WARNING: All knapweeds
may contain a cancer-causing agent.***
***Handle with extreme
Control: Integrated management approaches are necessary
to control this weed.
- Biological: There are 12 insect species cleared by the
USDA for use in controlling diffuse knapweeds. Each attack reduces
the plant's overall seed production by weakening the plant or
eating the seeds.
- Chemical: Herbicide application is effective. Chemical
use should be carefully coordinated with the use of biological
- Mechanical: Consistent hand pulling can be effective.
The Nature Conservancy reports initial infestations can be successfully
controlled with pulling three times a year for 5 years.
Report all sightings to your local