Foliar sprays with Steinernema carpocapsae against early-season apple pests

Persistence and field efficacy of the entomopathogenic nematode Steinernema carpocapsae All strain applied by foliar sprays were evaluated against the apple sawfly Hoplocampa testudinea and the plum curculio Conotrachelus nenuphar, two early-season pest in Quebec apple orchards. From 1992 to 1995, bioassays with Galleria mellonella larvae were conducted to assess the persistence of S. carpocapsae on leaves, flower clusters, and twigs up to 4 days after evening application. S. carpocapsae juveniles remained infective on apple leaves 24, 42, 98, and 24 hours after application in 1992, 1993, 1994, and 1995, respectively. In bioassays, the percentage of C. mellonella mortality was consistently higher on leaves (average = 84%), intermediate on flower clusters (73%), and lower on twigs (43%) for all application dates. In 1992 and 1993, single nematode sprays applied every 2 to 3 days from early May to mid-June on apple tree limbs reduced primary damage caused by H. testudinea by 98% and 100%, respectively, but none of the treatments was effective in 1994. In 1993 and 1994, multiple border-row sprays were applied against C. nenuphar adults with a commercial hand-gun applicator in an insecticide-free orchard. At harvest plum curculio damage in the nematode-treated orchard reached 5% and 55% in 1993 and 1994, respectively, as compared to 80% and 85% in an adjacent insecticide-free orchard. In a second experiment performed in 1994, multiple broadcast sprays with a commercial orchard sprayer caused no significant effect on plum curculio damage (nematode = 28%; control = 31%). Although some efficacy of canopy sprays of nematodes was detected against early-season apple pests, the inconsistent results and high application costs preclude their use as a sole control tactic against these pest in commercial apple orchards.