In various places in the world, aerial spraying of pesticides has met with resistance from local communities potentially endangered by toxic pesticide drift. Social movements, and the counter-expertise that they mobilise, often trigger changes in state regulations of the practice. This article describes such struggles over risk regulation in the Philippines, where aerial spraying is common in large monoculture banana plantations. It has provoked local activism contesting the socio-economic power of landed and business elites and has challenged the government’s approach to managing pesticide risks. This article develops the argument that different types of counter-expertise must be recognised. The case shows that it can be difficult for movements to articulate these different types of counter-expertise. Furthermore, the weak state characteristics of the Philippine state has shaped the ambiguous responses of risk governance to multiple actors’ divergent knowledge claims. The result is a legal impasse in which civil society has successfully pushed the issue of aerial spraying onto the national political arena, but the state has as yet been unable to develop a comprehensive pesticide risk regulation independent of powerful business interests.