Noxious weeds are estimated to inhabit over 100 million acres in the United States, and could be increasing by as much as 8-20% every year (US Department of the Interior 1997). Introduced and invasive weeds comprise an estimated 8-47% of the total plants in most states. In the West, noxious weeds have invaded over 17 million acres of public rangelands. Presently, an estimated 4,600 acres are invaded by noxious weeds each day (FICMNEW 1998).

          In 1994, the economic impact of weeds on the America economy was estimated to be more than $20 billion per year. Historically, a large portion of this cost was in agriculture, but growing weed problems impact industrial sites, roadsides, and other private and public lands. Close to $4 billion were spent in non-agricultural areas (FICMNEW 1998).