Noxious weeds are non-native plants introduced to North America from Europe and Asia.  These plants have spread at an alarming rate because, unlike native species, there are no native insects, fungi, or diseases to control their growth and spread.  Noxious weeds destroy wildlife habitat and forage, threaten endangered species and native plants, increase erosion and groundwater loss, and prevent recreational activities. Estimates are that noxious weeds have invaded approximately 17 million acres of public rangelands in the West - more than quadrupling their range from 1985 to 1995.  In northern California, yellow star thistle expanded its range from 1 million acres in 1981 to 10 million in 1997.