This paper analyses the use of metaphor in discourses around the “superweed” Palmer amaranth. Most weed scientists associated with the US public agricultural extension system dismiss the term superweed. However, together with the media, they indirectly encourage aggressive control practices by actively diffusing the framing of herbicide resistant Palmer amaranth as an existential threat that should be eradicated at any cost. We use argumentative discourse analysis to better understand this process. We analyze a corpus consisting of reports, policy briefs, and press releases produced by state extension services, as well as articles from professional and popular magazines and newspapers quoting extension specialists and/or public sector weed scientists or agronomists. We show how the superweed discourse is powered by negative metaphors, and legitimizes aggressive steps to eradicate the weed. This discourse reinforces the farmers’ techno-optimism master frame, contributes to deskilling of farmers and sidelines ethical concerns.