This paper describes a real-time implementation of an algorithm to segment plants, weeds, and soil in images used to control an autonomous crop protection vehicle. We show how the segmentation module fits in to the overall system and mention previous work on other modules. We then describe a segmentation algorithm and show how it is implemented on two digital signal processors (DSPs) controlled by a single transputer. We present timing information to show that the algorithm can provide data at 5 Hz, which is fast enough to control the vehicle.