"Biological invasions" are now recognized as the cause of significant ecological and economic damage. They also raise a series of less visible social issues. Management of invasive species is often a political process raising questions such as who decides which organisms are to be managed, and who benefits or is affected by different management techniques. In a rural region of northern California, the proposed use of herbicides on spotted knapweed sparked an intense social controversy. This research uses participant observation, interviews, and archival material to understand how members of the Karuk Tribe of California, the non-Indian community, and the U.S. Forest Service developed different perceptions of safety and risk regarding herbicide use. I describe interconnected factors that frame the interpretation of risk: institutional trust, proximity to exposure, gender, and race. Gender and race, in turn, form the basis of anti-herbicide mobilization. The larger sociological question highlighted is, who pays the price for species invasions? Use of herbicides on invasive species is increasing. Many people who face increased exposure to herbicides are members of racial minority groups. When the poor or racial minorities face disproportionate exposure, differences in risk perception become matters of environmental justice. This paper discusses the broader social implications of differences in risk perception among communities and land managers. (Contains 1 footnote.)