Outbreaks of the destructive coral-eating crown-of-thorns starfish, Acanthaster planci, present a considerable threat to coral reefs worldwide, and mitigating their impact has proven challenging. The most effective methods to control A. planci require injecting individual starfish with lethal chemicals. While some of these are highly effective, their administration often requires permits, training and access to specialised equipment. We aimed to identify a widely available and highly efficient alternative. We discovered that common household vinegar is lethal to A. planci individuals when injected at the base of one their arms. A single injection of 25 ml vinegar induced functional mortality in <24 h and 100 % mortality in <48 h. These results demonstrate that vinegar is an effective alternative to currently used chemicals. Vinegar is a viable alternative in the toolkit of methods that can control and eradicate local outbreaks of COTS on coral reefs.