Abstract Field studies were carried out from 2002 to 2004 in an olive grove near Cairo, Egypt, to evaluate the efficacy of the mating disruption to control the olive pest Palpita unionalis, during the 1st (May–June) or the 1st and the 2nd (September–November) distinct flight periods. The binary blend of the two pheromone components, E-11-hexadecenyl acetate and E-11-hexadecenal, at the ratio of 70:30 in hexane was dispensed from polyethylene (PE) vials or absorbed into montmorillonite and dispensed from PE bags at a dose of 80 g active ingredients per hectare. Efficacy was measured considering suppression of pheromone trap catches, reduction of the moth population and fruit damage during harvest in the pheromone treated compared to the control (CO) plots. Male captures in treated plots were reduced by 91.3% (2002), 91.8% (2003) and 80.6% (2004) during trapping periods of 8, 21 and 20 weeks, respectively. The number of eggs recorded and fruit damage were lower in the pheromone treated than in CO plot. The fruit infestation accounted to 13.6±2.7% vs. 37.8±3.9% in 2003, a low fruiting year and 9.7±0.75 vs. 34.8±2.8% in 2004, a high fruiting year in treated and CO plots, respectively. Capillary GC analysis indicated that the release rate of E-11-hexadecenyl acetate was effective for the testing period; whereas the release and degradation of E-11-hexadecenyl were high, the inclusion of a photostabilizer into the pheromone-clay complex during 2004 improved substantially the release rate and photooxidation of the aldehyde.