A system comprising a spray boom including a pair of boom assemblies, means for measuring the position of the boom assemblies relative to the ground, a stabilising device mounted on each boom assembly for stabilising and damping vertical movement of the spray boom, activating means connected to the stabilising device, and computer controlling means, wherein the stabilising device is configured as a block movable on a track along the length of the boom assembly thereby displacing the centre of gravity of the spray boom, the activating means capable of moving the block along the boom assembly, the computer controlling means receiving information from the means for measuring the position of the boom assemblies relative to the ground on the vertical movement of the pair of boom assemblies, whereby the computer controlling means controls the vertical position of the stabilising device through the activating means in response to received information.
