The leopard moth borer (LM), Zeuzera pyrina L., is a serious pest of walnut trees in semiarid regions of Iran. Chemigation, or irrigation in which an insecticide is incorporated into the irrigation water, is one strategy by which LM might be controlled. The experiment was carried out with five treatments in five replications in a completely randomized design in a 25 year-old walnut (variety Azarshahr at Kamalshahr) orchard in Karaj on 15 May, 2011. The treatments included imidacloprid SC350 at 20, 60, 100, 140 ml/tree and check (without spray). For sampling, 5 treated trees were randomly selected in each treatment. Ten annual branches were sampled in each tree and then the number of insect bore holes was counted in each 60 cm-branches individually. The mean numbers of bores per tree in imidacloprid treatments of 100 and 140 ml/tree were 14.25 and 8.25 bore holes, respectively, which were significantly fewer than the mean number of bores in the check (28). Lower imidacloprid treatments of 20 and 60 ml/tree had 32 and 38 bore holes per tree, respectively. Both of the last treatments could increase severity of LM infestation, whereas imidacloprid treatments of 100 and 140 ml/tree reduced LM infestation (50, 75%). The study showed that insectigation is a specialized method and should be carried out by a specialist knowledgeable about the physiochemical characters of the soil, tree physiology and pest biology; otherwise, this method can increase environmental pollution, LM infestation and the costs of pest control.