Hedgerow barriers and other reduced-risk controls for managing Oriental fruit moth, Grapholitha molesta (Busck) (Lepidoptera: Tortricidae) in apples

Management of Oriental fruit moth, Grapholitha molesta (Busck), in apple using an ‘Enhanced Integrated Pest Management (IPM)’ program comprised of a hedgerow barrier, pheromone-based mating disruption and reduced-risk [non-organophosphorous (OP) or carbamate] insecticides was investigated over a 5-year period. The barrier was comprised of a planting of three rows of hybrid poplar, Populus deltoides Bartr.×Populus nigra L., one row of Italian alder, Alnus cordata L. (nectar reward), and one row of white pine, Pinus strobus L. The hedgerow completely surrounded the perimeter of the apple orchard and was treated with garlic and a low rate of pyrethroid insecticide in 4 of the 5 years. The Enhanced IPM program significantly reduced G. molesta populations as measured by moth captures in pheromone traps. Captures of G. molesta were significantly higher in apple orchards treated with OP and carbamate insecticides, ‘Conventional IPM’, and either not surrounded by the hedgerow or with the barrier present but not treated with the repellent compounds. To explain these differences in G. molesta control, and the potential non-lethal effect of hedgerow barriers on G. molesta orchard colonization, we studied the adult vertical movement in a traditional unsprayed standard apple orchard at three different heights: 0.95, 1.95 and 3.20 m, respectively. In the overwintering generation at a height of 0.95 and 1.95 m, the mean number of moths captured per sampling period was 14.64 and 14.84, respectively, and only 2.95 at 3.20 m. However, the number of individuals captured in the second and third generations was not significantly different at the three different heights. Fruit damage evaluated before ‘June drop’ closely corresponded to the distribution of moths captured during the overwintering generation. Fruit damage at a height of 1.95 and 3.20 m was 5.8 and 3.5%, respectively. These results indicated that G. molesta is a weak flyer and that hedgerow barriers exerted some influence in the colonization of the orchard by limiting the free movement of adults from the overwintering generation. Thus, hedgerow barriers seem to limit early migration and establishment of G. molesta in the orchard. This in turn may reduce the size of the following generations and makes subsequent control easier under the Enhanced IPM program.