other knapweeds, Russian knapweed is native to Eurasia (central
Europe and East to central Russia) and was introduced into America
around 1898. It is now considered a noxious weed in 21 Western states.
Russian knapweed plant can produce over 1,200 seeds, each remaining
viable for 2-3 years. Seeds are known to be dispersed by some mammals,
recreationists, crop harvest, transportation of infested topsoils,
and contaminated vehicles. Seed dispersal allows this plant to spread
into new areas, but once established, most reproduction within a
site comes from adventitious
buds on their black roots. Roots can grow 6-8 feet deep the first
year and 16-23 feet the second year. They also release allelopathic
chemicals that stunt the growth of many of the surrounding native
plants. Over time, Russian knapweed can out-compete and crowd out
native plants and form a monoculture.
properties and aggressive competition reduce plant biodiversity.
This plant loss reduces forage for a number of wildlife and domestic
animals. It is very toxic to horses wet or dry, causing the neurologic
disorder named "nigropallidal encephalomalacia". Any cropland invaded
by this plant is usually abandoned due to the cost of its control.
may be grazed.
knapweed often appears in areas that have a shallow water table
(less than 20 feet deep) or that received extra water from irrigation.
It invades open sites that have been recently disturbed or heavily
grazed. These sites include: cultivated fields, orchards, pastures,
roadsides, and rangelands.
of the following tools is best:
• The most effective management strategy is promoting plant competition.
Establish competitive, desired plants in disturbed areas and infested
sites. Cool-season perennial grasses have worked well.
has a short-term success, but is not highly effective (example
herbicides: Roundup, Tordon 22K,Curtail, Telar [look
at herbicide label: free search]).