Biological control of Oligonychus perseae (Acari: Tetranychidae) on avocado: IV. evaluating the efficacy of a modified mistblower to mechanically dispense Neoseiulus californicus (acari: phytoseiidae)

Abstract

A Stihl SR400 backpack mistblower was modified to mechanically dispense the phytoseiid predator, Neoseiulus californicus (McGregor) onto artificial and actual avocado trees. The ability of the mistblower to broadcast N. californicus vertically was initially evaluated on a group of four artificial trees (4 m height). Distribution of corn grits, the carrier material in which N. californicus is commercially packaged, was unevenly distributed. Analysis of sticky cards arranged at 0.5 m intervals on artificial trees indicated that 75% of grits adhered to cards at heights ranging from 1.5-3.5 m. In an avocado orchard, the efficacy of three treatments for dispensing N. californicus was assessed: (1) mistblower application of phytoseiids mixed with corn grits with water setting on 0.5 (provided a fine spray to adhere predators and grits to leaves); (2) mistblower application of phytoseiids mixed with corn grits with water setting on 1.0 (provided a coarse spray); and (3) 4-point hand-release of predators into 10 paper cups placed evenly around trees at shoulder height. Each release strategy used about 19,000 predators and all treatments were compared to control trees that were not treated with N. californicus to determine naturally occurring densities of this predator on experimental trees. The mistblower successfully dispensed viable N. californicus mixed with com grits onto avocado trees. Predators on trees treated with the mistblower were recovered in the field up to 16 days post-application. However, 5-fold higher levels of N. californicus were recovered from hand-release applications. These tests on artificial trees and avocado trees demonstrated the potential of the mistblower for field applications of viable phytoseiids for control of spider mites on trees.