Suppression of pear psylla, <i>Cacopsylla pyricola</i> (Hemiptera: Psyllidae), with fall applications of kaolin clay

Pear psylla, Cacopsylla pyricola (Förster), is a key pest of pears in the Pacific Northwest United States. Overwintering adults (winterforms) recolonize orchards in late winter from habitat outside orchards. To reduce winterform colonization and subsequent damage, sprays of the repellent particle film, kaolin clay, are recommended from late dormant through bloom. However, many pear growers struggle to make early sprays due to the danger of driving tractors over hilly terrain with lingering winter moisture. To address this challenge, we tested fall applications of kaolin (Surround WP) for suppression of pear psylla the following spring. Experiments were performed on potted trees and commercial orchard-sized plots, with fall kaolin treatments made at 112 kg/ha (120 g/L). Pear psylla adult and egg densities were measured by visual counts, and kaolin residue stability was assessed by relative whiteness of branches using ImageJ. In the days immediately after kaolin applications (fall and spring), kaolin significantly reduced pear psylla adult numbers and increased branch whiteness. Fall kaolin residues visibly declined over the winter, but branches often remained significantly whiter than checks at spring assessments. Likewise, fall kaolin often resulted in significantly fewer adults and eggs than checks the following spring. This study demonstrates that residues from fall-applied kaolin can remain through the winter and reduce pear psylla colonization the following spring. This tactic will be advantageous in orchards that are difficult to spray in early spring, and as a general addition to the pear integrated pest management toolkit.