Using the Nematode, Steinernema carpocapsae, to Control Peachtree Borer (Synanthedon exitiosa): Optimization of Application Rates and Secondary Benefits in Control of Root-Feeding Weevils

Abstract

The peachtree borer, Synanthedon exitiosa (Say) (Lepidoptera: Sesiidae), is a major pest of stone fruits including the peach Prunus persica (L.) Batsch. The entomopathogenic nematode, Steinernema carpocapsae, was previously shown to be an effective tool for controlling S. exitiosa. In orchards where irrigation is not available, a sprayable gel (Barricade®) can be used to maintain soil moisture which can facilitate nematode efficacy. However, rates of nematode and Barricade® application had not been optimized for their maximum economic and biocontrol efficiency. Therefore, our objective was to compare rates of S. carpocapsae and Barricade® in field trials. Nematodes were tested at per-tree application rates of 1.5 million, 1 million and 0.5 million infective juveniles. The sprayable gel was used at two rates, 4% and 2%. A reduction in the used nematodes from 1.5 million to 0.5 million per tree showed no difference in efficacy. Similarly, using the gel at half rate also did not impact the efficacy, and treatments containing nematodes controlled the S. exitiosa better than the chlorpyrifos control in several of the tests (p < 0.05). As an added benefit, the nematode treatments were also able to reduce the prevalence of weevil (Coleoptera: Curculionidae) populations as secondary pests of the peach trees. The lower rates of grower inputs will reduce costs, making the nematode biocontrol of the peachtree borer more likely to be adopted by commercial growers of peach.