Phenology and management of noctuids attacking apple in Central Otago, New Zealand

Abstract

Noctuids are minor pests of apple crops in New Zealand. Leaf and fruit clusters on apple trees at the Clyde Research Centre were monitored for the presence of eggs and larvae of noctuids and their damage from petal fall to harvest in three growing seasons 1995 to 1998. Over the same period, pheromone traps for the two taxa of Graphania mutans ‘South’ and ‘North’ were operated in the same apple blocks, and continued for the ‘South’ taxon until 1999-2000. Eggs could be found on the trees from spring to harvest but not in every season, whereas larval presence and fresh damage was almost confined to the period from petal fall to the end of December and comprised only young larvae. G. mutans constituted about 95% of all noctuid eggs and larvae. The time and magnitude of catches of the two taxa in the pheromone traps were extremely similar, with a peak flight over apple flowering, a trough at the end of December, and an extended further flight(s) with peak numbers usually in January/February but catches extending to May. From 1998 to 2000, 21–22 apple blocks in Central Otago commercial orchards were monitored with pheromone traps (‘South’ taxon) and/or by sampling fruit clusters for noctuid eggs, larvae, and damage over the flowering and fruit set period (Oct-Nov). Harvest sampling in the same blocks demonstrated a strong linear relationship of ‘harvest damage to fruit’ with ‘spring foliage damage to fruit clusters’. An initial action threshold for spring insecticide application was derived from this relationship as >5 out of 200 fruit cluster with leaf damage but further analysis now suggests doubling this threshold. There was only a weak relationship between pheromone trap catches and damage in spring or at harvest. Photographic records of the same damage to apples in spring and at harvest were used to determine unequivocally the separation of noctuid damage from other causes. Two noctuid species, Graphania plena and Agrotis ipsilon aneituma, were found for the first time to cause occasional damage to apples in spring.