Will it stick? Suppressing spring pear psylla with autumn-applied kaolin

Pear psylla, Cacopsylla pyricola, is the most challenging pest of pears in Washington and Oregon. Adults invade orchards and begin laying eggs from February to April. Surround WP (kaolin clay), a sprayable white powder that deters insect pests, has become a critical component of early season pear psylla IPM. Unfortunately, pears are often grown on steep hillsides where snow and ground moisture make spraying dangerous well into the spring. Surround WP is formulated with a sticking agent that allows residues to persist for long periods and through adverse weather, so it is possible that a late autumn application, when it is safer to spray, could persist through winter and provide suppression of pear psylla the following season. We tested this hypothesis over two experimental seasons on 2-acre commercial orchard plots and in corresponding choice test experiments using outdoor potted trees. Treatments were autumn-applied Surround, spring-applied Surround, or no Surround (check). Psylla adults and eggs were counted in plots and kaolin residues on branch cuttings were measured using Image J. In both commercial orchards and potted tree experiments, autumn-applied Surround had significantly fewer psylla adults and eggs than checks and similar densities to spring-applied Surround. Residues of autumn-applied Surround degraded over time and were less detectable than fresh applications in the spring, but were detectable, nonetheless. Our results suggest that autumn-applied Surround WP can benefit pear psylla management programs, especially for orchard blocks on steep terrain that is unsafe for early season spraying.