Curative Control of the Peachtree Borer Using Entomopathogenic Nematodes.

The peachtree borer, Synanthedon exitiosa (Say 1823), is a major pest of stone fruit trees in North America. Current management relies upon preventative control using broad-spectrum chemical insecticides, primarily chlorpyrifos, applied in the late summer or early fall. However, due to missed applications, poor application timing, or other factors, high levels of S. exitiosa infestation may still occur and persist through the following spring. Curative treatments applied in the spring to established infestations would limit damage to the tree and prevent the next generation of S. exitiosa from emerging within the orchard. However, such curative measures for control of S. exitiosa do not exist. Our objective was to measure the efficacy of the entomopathogenic nematode, Steinernema carpocapsae, as a curative control for existing infestations of S. exitiosa. In peach orchards, spring applications of S. carpocapsae (obtained from a commercial source) were made to infested trees and compared with chlorpyrifos and a water-only control in 2014 and 2015. Additionally, types of spray equipment were compared: nematodes were applied via boom sprayer, handgun, or trunk sprayer. To control for effects of application method or nematode source, in vivo laboratory-grown S. carpocapsae, applied using a watering can, was also included. Treatment effects were assessed 39 d (2014) or 19 d (2015) later by measuring percentage of trees still infested, and also number of surviving S. exitiosa larvae per tree. Results indicated that S. carpocapsae provided significant curative control (e.g., >80% corrected control for the handgun application). In contrast, chlorpyrifos failed to reduce S. exitiosa infestations or number of surviving larvae. In most comparisons, no effect of nematode application method was detected; in one assessment, only the handgun and watering can methods reduced infestation. In conclusion, our study indicates that S. carpocapsae may be used as an effective curative measure for S. exitiosa infestations.