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This article examines the biosecurity management of invasive species, focusing on the case of the control of ragweed ( Ambrosia artemisiifolia), an invasive plant with allergen pollen. An ethnographic survey was conducted in France’s Rhône-Alpes region among local residents’ communities, farmers, and inhabitants. I analyze the social organization of surveillance along with the imaginaries and techniques of controlling the spread of the ragweed, highlighting their specific relationship with singular living. Considered as biological pollution, ragweed upsets the traditional categories that we use to consider nature. Its management is structured around participatory monitoring, which places most of the responsibility on farmers. However, the failure to control the ragweed leads us to reconsider the causes of its spread, in connection with the anthropization of land occupation. The approach hereby chosen rejects constructionism in order to leave room to consider the singularity of the plant in its material expressions and ecological interactions.