Methods, systems, and apparatus, including computer programs encoded on computer storage media, for controlling spraying of chemicals by an unmanned aerial vehicle (UAV). An unmanned aerial vehicle system includes one or more processors configured to perform operations of autonomously performing a flight path by the UAV and dispersing a chemical by the UAV along portions of the flight path. The UAV may include a chemical spray system having one or more spray booms with multiple nozzles for dispersing a chemical. The chemical spray system may include one or more tanks attached to the body of the UAV and a pump fluidly connected to the tanks to disperse chemical via the spray booms.