knapweed is a native of Eurasia, probably introduced to North America
about 1898. This plant is considered a noxious weed and is included
on the Colorado and the Adams County Noxious Weed Lists. Russian
knapweed is an aggressive perennial (lasts several years) weed that
reproduces from seed and adventitious buds on a creeping root system.
plant is allelopathic, which means it exudes toxins into the soil
so that no other plant species can grow around it. Dense colonies
are usually formed by the widely spreading black, bark-covered roots. Stems are covered with fine, white hairs that give the stem a blue-green
color. Stems are erect, openly branched, with plants standing up
to 3 feet tall. Flowers
are pink to lavender in color, and are surrounded by pearly, rounded
bracts with papery margins that are smooth to the touch.
knapweed invades open, disturbed land, cultivated fields, along
ditch banks, fence rows, roadsides, and in waste places. Once established,
it tends to form a single-species stand and is very difficult to
control or eradicate. Russian knapweed infestations reduce forage
for livestock, and greatly reduce biodiversity for wildlife habitat.
Plants ingested as fresh or dried forage are toxic to horses, causing
a nervous disorder called "chewing disease".
1,400,000 acres in the western United States are infested. Roughly
30,000 of those acres are infested in Colorado.