NAVEL ORANGEWORM IN SOUTHERN CENTRAL VALLEY WALNUTS: SOURCE, SEASONAL ABUNDANCE, AND IMPACT OF MATING DISRUPTION

The navel orangeworm is considered the principle insect pest of almonds and pistachios in California, but generally of secondary importance in walnuts. In the former nut crops, however, there is a gradient of navel orangeworm abundance and damage, with less damage in the north and more to the south. Efficacy of mating disruption for navel orangeworm has been demonstrated in almonds, but separate examination of mating disruption in walnuts is important due to a very different canopy structure compared to walnuts. In 2012 we examined abundance of navel orangeworm in walnuts the southern portion of the California growing area, and the impact of mating disruption on navel orangeworm in this crop. Traps with unmated females as a pheromone source found cohort structures of male abundance similar to those observed in almonds. Extensive arrays of egg traps captured many eggs during first flight, but few during subsequent flights. Comparison of males in pheromone traps with distance to other tree nut crops, and spatial analysis of egg trap captures in a walnut site adjacent to almonds suggest that this year-around navel orangeworm abundance at these sites is not due to principally to immigration from other crops. Biological impact of mating disruption was demonstrated; i.e., near-complete suppression of males captured in female-baited traps and significant reduction eggs captured in egg traps, demonstrating both disruption of sexual communication and impact on fertility. Insect damage at harvest was >10% in some cases. The impact of mating disruption on this harvest damage was less clear than the biological impact, although this was also true of grower standard insecticide treatments in the absence of mating disruption. Comparison of seasonal abundance of navel orangeworm and codling moth suggests that insecticides targeting codling moth flight 2A would also impact the second navel orangeworm flight, but that the first navel orangeworm flight would be less affected by insecticides timed against the 1B codling moth flight. OBJECTIVES 1. Characterize seasonal abundance of navel orangeworm in southern Central Valley walnuts, and compare these data with codling moth abundance and walnut infestation by these two pests.