Cultivation of genetically modified soybeans with the use of herbicides is now becoming widespread in Argentina. This work addresses an emblematic case of knowledge articulation between experts, professionals and communities, namely, the case of an association of people affected by fumigation Grupos de Pueblos Fumigados (GPF). The GPF warns against agrochemical spraying in urban areas, and its activists collect and disseminate information about its impact with a view to banning the practice. Here, we apply Parthasarathy’s framework, used to analyse the strategies employed by activists to break the expertise barrier, to the case of the GPF, adding a new category to her original four strategies. There is an institutionalizing potential in these social and environmental movements, many of which are organized in the form of Civic Assemblies. The composition of the assemblies reflects a heterogeneous and multi-sectorial character; they articulate a new kind of knowledge that can be an appropriate interlocutor for traditional expert knowledge.