Mating disruption of pecan nut casebearer, Acrobasis nuxvorella Neuzig, was evaluated using the single component sex pheromone, (9E,11Z)-hexadecadienal in four field experiments in commercial orchards of pecan, Carya illinoinensis (Wangenh.) K. Koch. The sex pheromone was formulated as either: 1) Microbead: a 5% microencapsulated sprayable or 2) Paintball: a latex sphere containing the sex pheromone formulation and designed for application with a paintball gun. Evidence of mating disruption was measured by comparing the number of pecan nut casebearer moths captured in sex pheromone-baited traps; numbers of viable, non-viable, and eclosed eggs; and nut damage by larvae in the sex pheromone treatment relative to the numbers in the nontreated check. In all four experiments, the sex pheromone treatment significantly reduced by 89.6% or more the number of captured pecan nut casebearer moths relative to the nontreated check. However, in three experiments, there was no significant reduction in the mean numbers of viable, non-viable, and eclosed eggs, or nut damage in the sex pheromone treatment compared to the nontreated check. In another experiment, the mean numbers of viable and eclosed eggs, percentage of infested nut clusters, and nuts damaged by pecan nut casebearer larvae were significantly less in the sex pheromone treatment than in the nontreated check. Based on the results of this experiment, application of sex pheromone before capture of the first pecan nut casebearer moth and two or three applications of sex pheromone at a rate of 6–10 g per hectare per application were necessary to disrupt mating. These experiments are the first to demonstrate the reduction of pecan nut damage resulting from the use of pecan nut casebearer sex pheromone to disrupt mating. However, the lack of control observed in three of the four experiments suggests further studies are needed to better understand and enhance the efficacy of pecan nut casebearer mating disruption.