The recent availability of sex pheromone lures for the navel orangeworm, Amyelois transitella (Walker) (Lepidoptera: Pyralidae), improves options for monitoring this key pest in conventionally managed almonds. These lures are, however, minimally effective in the presence of mating disruption. Experiments were conducted to determine if phenyl propionate (PPO), an attractant for the navel orangeworm, acts in an additive or synergistic manner when presented together with the pheromone. In the absence of mating disruption, traps baited with PPO captured significantly fewer adults than traps baited with a sex pheromone lure. There was no difference in the number of adults captured in traps with both attractants when mating disruption was not used. In the presence of mating disruption, pheromone traps were completely suppressed, yet traps with both pheromone and PPO captured significantly more adults than traps baited with only PPO. Traps with only PPO captured equal numbers of both sexes, whereas traps with both attractants had significantly more males. These findings demonstrate that PPO is likely to be useful for monitoring navel orangeworm in fields treated with mating disruption.