ABSTRACT
The role of the United States Department of Agriculture, Agricultural Research Service (ARS) in the research and control of introduced weeds is discussed. Introduced weeds are a major economic threat to the United States. Currently, about 60 % of all weeds in the United States are of foreign origin. These alien weed species reduce the quality of food, feed, and fiber and increase the cost of crop production by several billion dollars annually. In addition, introduced weeds threaten native plant species in natural areas and reduce environmental quality on public and private lands.