Border-Row Sprays for Control of the Plum Curculio in Apple Orchards: Behavioral Study

Abstract

In spring 1987, 215 65Zn-labeled adult plum curculios, Conotrachelus nenuphar (Herbst), were released, just after they emerged from overwintering, at a single site located at the southern edge of a woodlot bordering an unsprayed apple orchard in southern Quebec. At petal fall, between the second and third day of release, a border-row spray of insecticide was applied to the two perimeter rows of apple trees in front of the release site. Dispersal of the population was compared with another group of 254 curculios released simultaneously in the center of the 1.7-ha orchard. In 1988 and 1989, the borderrow spray was applied to the entire orchard perimeter. Plum curculio damage at harvest was assessed and compared with that found in a nearby unsprayed apple orchard. Labeling had no significant effect on field mortality and behavior. Insects released at the edge of the woodlot moved toward the orchard. Mortality was three times higher for insects dispersing through the sprayed rows than for those dispersing in the center of the orchard. Among insects that were recaptured in the orchard and at its edge, 83% were found either dead under the sprayed trees (59%) or alive along the outside edge of the sprayed rows (24%). The remaining curculios (17%) were found alive within the orchard. Plum curculio damage at harvest decreased from 1987 (52%) to 1989 (2.4%), whereas in a nearby unsprayed apple orchard, it averaged 70% (minimum 43%, maximum 88%). A single petal fall border spray was moderately effective in protecting fruit, but the combination of a pink spray and a petal fall border spray provided economically acceptable control. Reinfestation after the petal fall spray appeared to be the main cause of plum curculio damage at harvest. Toads, Bufo americanus americanus Holbrook, were found with high levels of 65Zn. Ways to improve the efficiency of plum curculio control by border-row spraying are discussed.