Fall kaolin sprays suppress next spring’s psylla, 2020-2021 season update

Written by Robert Orpet and Louis Nottingham, WSU TFREC, Entomology October 2020.

Kaolin clay (Surround WP) is a white sprayable powder that discourages pear psylla from laying eggs on pear trees by creating a physical barrier over the tree’s surface. If sprayed early in the season, the white coating could also deter psylla from colonizing orchards, possibly due to repellency of reflected UV light to insects. Kaolin is more persistent on trees than most insecticides, especially when used with a spreader-sticker (check labels for compatibility and mixing instructions), and it has low risk of harming natural enemies because it is non-toxic. Kaolin also provides sun protection to trees, making it beneficial from a horticultural standpoint. Additional notes on particle films for pre-bloom management of psylla can be found in a previous article (https://treefruit.wsu.edu/article/prebloom-management-of-pear-psylla-with-particle-film/).

In experiments from 2017-2018 and 2018-2019 (https://treefruit.wsu.edu/article/fall-kaolin-sprays-suppress-psylla-next-year/) we found that Surround WP sprayed at the experimental rate of 100 lbs/acre on pear trees in late October or early November during leaf drop persisted on trees over the winter (Figure 1) and contributed to pear psylla adult and egg suppression the following springs (Figure 2).

Further understanding the utility of fall-applied kaolin may fill a hole in current management because psylla colonization and egg lay often occurs before the first sprays of the season are possible. For example, in the spring of this year (2020) in Wenatchee, we observed egg lay started in late February, long before most growers would typically plan or be able to spray. In this situation, application of kaolin in the fall could be a useful preventative measure to cover the period of early winterform adult movement into orchards and oviposition before spring sprays.

This year we are continuing to experiment with fall-applied kaolin on large commercial plots in Wenatchee, WA, Hood River, OR, and Medford, OR to further validate the efficacy of fall kaolin and assess commercial viability. We are also conducting small plot experiments in Wenatchee to examine a more basic grower inquiry: do the early-laid eggs on wood contribute to the first generation of nymphs, or are these eggs less important (or not at all important) compared with eggs laid on green bud tissue?

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