Abstract We investigated the potential of disrupting pheromone-mediated mating communication in European corn borer, Ostrinia nubilalis (Hübner). The female sex pheromone, a blend of (Z)-11-tetradecenyl acetate and ( E)-11-tetradecenyl acetate in a ratio of ∼97 : 3 was released from two dispenser types and in two deployment patterns, a Shin-Etsu rope formulation spaced 2 m apart and a widely-spaced (35 m) pattern using a controlled release system called the Metered Semiochemical Timed Release System (MSTRS TM). Both dispensers were situated in grassy sites that constitute aggregation areas for O. nubilalis mating activity within and around cornfields at three different locations in Iowa. Pheromone-emission rate (after 7 days in the field) from the MSTRS TM (6.09 μg/min) was ca. 26 times greater than from the rope formulation (0.23 μg/min). Both dispensers during both first and second flights achieved a significant level of disruption of pheromone-source location (averaging 97%). More importantly, a significant level of mating disruption was achieved, as measured by the frequency of mating by free-flying feral females. The mean number of matings, as measured by spermatophores, per first generation female was 1.33 in the MSTRS TM plots and 1.58 in the rope plots, compared with 1.88 in untreated check plots. During the second flight, the number of matings per female averaged 1.63 in the MSTRS TM plots, 1.56 in the rope plots and 2.17 in untreated check plots. There was also a significant reduction in the proportion of females that mated at least once during both flights in MSTRS TM plots. During the first flight, 17 and 10% fewer females mated in the MSTRS TM-treated and rope-treated fields, respectively. A similar level of disruption was also achieved during the second flight.