Weed detection and/or destruction

A method of determining the position of weeds growing in soil amongst crops comprising the steps of:- Using a camera to acquiring a stereoscopic image of plants growing on soil; - Segmentation plant pixels and soil pixels; - Creating a modelised height profile of the soil at positions at which soil pixels have not been captured by the stereoscopic image based on information derived from adjacent soil pixels; - Determining a corrected plant height at plant pixels representing the distance between the plant pixel and the modelised soil underneath; - Differentiating between weeds and crops by ciomparing the corrected plant height with an expected crop height. Once the position of a weed has been determined, it may be destroyed, for example by heat applied to the identified position or by a robotic arm.