12-Spotted Knapweed

Spotted knapweed (Centaurea steobe) is a perennial tap-rooted plant introduced to North America about from Eastern Europe probably as a contaminate of alfalfa seed or ship ballast. 

It is currently reported in all but three states in the U.S. and infests an estimated 7 million acres. Knapweed spreads by seed and produces an average of 1000 seeds per plant.

Celestine Duncan

Celestine Duncan

USDA Plants Database

USDA Plants Database

Impacts

Spotted knapweed reduces grass production 60 to 90% impacting wildlife and livestock resources.  It also: increases soil erosion; reduces species richness; threatens rare and sensitive species; increases human allergies; and reduces land values.  In 1996 the economic impact of spotted knapweed in Montana was calculated at $42 million annually in direct and secondary losses.

Status

Considered a noxious or prohibited weed in 16 states.