Abstract: A water balance control for a pivotal end boom connected to the outer end of a center pivot irrigation system to irrigate peripheral areas (e.g., corners) beyond the periphery of the circular area covered by the main conduit of the system; the water balance control comprises a sensing mechanism for sensing both the angular position of the boom and its direction of movement (swing-out or swing-in) relative to the end of the main conduit. Primary control circuits, actuated by the sensing mechanism, turn the boom nozzles on and off, depending on the angular position of the boom; secondary control circuits, also actuated by the sensing mechanism, operate the primary controls in accordance with two different programs, one for swing-out movement and the other for swing-in movement. A speed control for the main conduit, also actuated by the sensing mechanism, is included.