Stevens County Noxious Weed Control
Board This web site will help
you identify & control noxious weeds. Conventional & biological control
(BioControl) information and photographs are here. Maps & related
information are included.
Russian knapweed
Acroptilon repens
Sunflower
Family
Key identifying traits
Black to brown scaly roots produce stem buds
Cone shaped heads with light pink to purple flowers
Bracts surrounding each flower are paper like
Forms dense colonies from root shoots
Stems and leaves covered with fine hair, giving a blue or gray–green
color
Stems are erect, openly branched, 18 to 36 inches tall
Biology and ecology
Tap-rooted perennial with limited seed production
Spreads mainly by underground rootstocks
Flowers June through September
Invades cultivated fields, pastures and roadsides
Roots penetrate to a depth of over 8 feet
Ingestion of substantial amounts can be fatal to horses
Grazed readily and without ill effects by other livestock
Control
Prevention-
Learn to
identify the plant; know your property; beware of fill dirt, hay and seed
from outside your area
Biological –A gall forming nematode established in
Washington may eventually assist control
Cultural –Competitive vegetation helps avoid initial
infestation, but Russian knapweed can invade healthy plant communities
Mechanical –Mowing, pulling and cultivation are
ineffective controls because of root spread
Chemical –
Several
effective at label rates, but timing is critical with bud stage and after
a light frost being the two best times;
refer to the
PNW Weed Management Handbook for specific chemical recommendations
press of heads/stems
seedlings
infestation
roots & flower head
Where found –
Scatteredsites along roadsides, pastures and cultivated fields in most regions
of Stevens County.
