Preliminary results from a multistate validation of the insecticide termination rules of the COTMAN expert system are discussed. COTMAN recommends insect control be terminated at 350 heat units after the flower date of the last effective boll population. Small plot experiments in Arkansas, Texas and Louisiana show no significant yield difference from terminating insect control for bollworm and boll weevils at NAWF=5 + 350HU. Large plot experiments in Arkansas, Texas and Mississippi demonstrated higher yields, lower insect control costs and higher net revenues from following the COTMAN termination rules.