Efficacy of horticultural oil(s) thermotherapy towards pear psylla suppression

Abstract

This study evaluated mortality of winterform pear psylla after treatment with four commercially available horticultural oils delivered in both heated and non-heated sprays. The aim was not to compare efficacy of the oil products, rather validate previous studies reported on efficacy of heated oil spray (HO) using various oils. Furthermore, this study aimed to validate fumigation effects of heating oils through additional investigation of the efficacy of a heated water spray (HW) treatment. Four oil products – Cinnerate®, Thyme Guard®, Purely Green Bio-Pesticide and PureSpray™ Green – were tested at minimum label recommended concentrations. For each oil product, the following treatments were conducted: 1) untreated control, 2) HW spray, 3) unheated oil (UO) spray, and 4) HO spray. Each treatment was replicated 5 times against winterform adult pear psylla in a bioassay format. The spray was applied using a single hollow cone nozzle (D8DC45, VMD = 165 μm) at 0.3 and 0.6 m from the target organism. Mortality was evaluated at 24 hours after spray. Regardless of oil product, when applied at 0.3 m from the psylla, the mortality response for HO was not different from HW, but both had significantly higher mortality than the control. At 0.6 m from the nozzle, HW failed to increase psylla mortality relative to the control. However, Purely Green Bio-Pesticide, significantly increased psylla mortality relative to the HW treatment, but heating this specific oil did not alter its efficacy. Similarly, remaining pesticide products failed to show significant difference between HO and UO applications at 0.6 m. Overall, spray distance appears to be a limiting factor for successful delivery of a heated spray, and that tested oils did not improve their efficacy with heating.