Apple Leafroller (Lepidoptera: Tortricidae) Populations and Parasitism in an Orchard Managed With Either a Grass or Alfalfa Cover and Without Insecticides Over Four Growing Seasons

Abstract

Northwest U.S. apple growers are concerned that with reduced insecticide use leafrollers will become serious economic pests. Concomitantly, interest in integrating legume covers in the agro-ecosystem, to augment orchard nitrogen nutrition, increases. We evaluated leafroller populations and parasitism in apples with grass or alfalfa covers and curtailed insecticide use. For both covers, the leafroller populations rose to high levels then dramatically declined the fourth year of the study. Parasitoids modestly contributed to leafroller biological control. Only in a few instances, parasitism rates were higher in alfalfa cover plots compared with grass cover plots. Six parasitoid species contributed to leafroller biocontrol. Yield was not substantially adversely affected by leafrollers.