Many of the world's most challenging environmental problems are trans-boundary in nature, requiring the cooperation of diverse actors. This study aims to assess the roles of trust and power in achieving environmental collective action among rural land managers. The empirical example used is serrated tussock (Nassella trichotoma), a highly invasive, noxious weed that covers more than two million hectares in south-eastern Australia. Semi-structured interviews were used to explore relations among the suite of actors responsible for controlling this weed in two case studies-Cooma, NSW and Bacchus Marsh, Victoria. Interactions between trust and power were found to be useful for explaining the development of positive and negative relations among these diverse actors. When trust and power worked in synergy, land managers and government staff were more likely to share information, provide support and defer to enforcement. When trust and power acted as substitutes avoidance, disengagement, resistance and retaliation ensued. The author argues that long-term collective weed control will only be achieved when the focus shifts from enforcement to building stronger rural social relations in which trust and power work in synergy.