Russian knapweed
From Wikinfo
Russian knapweed, Acroptilon repens, is an invasive weed which infests rangeland. It is often found as an impurity in hay and may spread though infested hay. In 2002 over 100,000 acres in Colorado were reported infested with Russian Knapweed. The weed actually is native to the steppes of Eurasia and grows thoughout the rangelands of the American West.
Russian knapweed is a woody perennial herb which grows from 6 to 18 inches high with dull green lanceolate foliage and light purple or pink flowers. It grows in patches linked by a web of roots. Pulling a plant cause it to break off, leaving the root which buds, propagating a new plant. Russian knapweed excretes chemicals which retard the growth of competing plants, allelopathy.
Effective control of Russian knapweed depends on constant pressure on the plant. The key is to eventually exhaust the reserves of the root system. Controlling knapweed can prove quite expensive; therefore, weed control organizations often offer to share the cost with private landowners who agree to undertake control [1]
As a patch of knapweed will have eliminated other vegetation, after it is eliminated, something else must be planted to fill the void, turf type perennial grasses are the most effective replacement.
