Efficacy evaluation of horticultural oil based thermotherapy for pear psylla management

The goal of this study was to improve techniques for pear psylla, Cacopsylla pyricola (Föerster) control, one of the major pests in pear orchards worldwide and in the United States. Mortality of adult pear psylla was determined after its exposure to horticultural oil (HO) combined with high temperature (thermotherapy) treatments. A laboratory-scale application technology unit was developed to apply HO-based thermotherapy. Spray treatments included four variables namely heat-condition (i.e., heat and no-heat), HO concentration (i.e., 0.5 and 1.0%), nozzle types (i.e., N1: Conejet nozzle, N2: D2/DC13 disc-core nozzle) and application pressure (i.e., 344.7 [50] and 689.5 [100] kPa [psi]). Each treatment was replicated four times on pear psylla bioassays. Mortality was evaluated at 3, 6, 12, 24 and 48 h after spray application. HO combined with thermotherapy achieved as high as 100% pear psylla mortality during early hours after spray application. The overall mean pear psylla mortality using HO under heat condition (63.7 ± 2.4% [mean ± std. error]) was significantly higher compared to no-heat condition (43.6 ± 1.8%). Higher HO concentration (i.e., 1.0%) under heat condition had significantly higher mortality (60.2 ± 2.3%) compared to similar applications at lower concentration (47.1 ± 2.0%). Pear psylla mortality was significantly affected by nozzle type under heat conditions, and nozzle N1 (with comparatively higher spray coverage on water sensitive papers) had significantly higher (74.4 ± 3.1%) pear psylla mortality compared to nozzle N2 (52.9 ± 3.3%). The interaction between thermotherapy and each of the HO concentrations and nozzles on psylla mortality was significant at α = 0.05. Overall, HO combined with thermotherapy caused a rapid kill of pear psylla. Future field studies are warranted to evaluate efficacy of HO-based thermotherapy at reduced HO concentrations and pertinent effects on smothering of eggs and pear psylla mortality.