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Pear Psylla Phenology Update

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Written by Louis Nottingham, May 2021.

A phenology model for pear psylla was recently developed by Dr. Vince Jones. This model predicts the relative number of pear psylla from each life stage occuring as degree days are accumulated. Below is a graph showing the psylla degree day model and the status of psylla development on May 6th 2021. Degree days were averaged among weather stations in Medford, OR, Hood River, OR, Wapato, WA and Cashmere,WA; the difference from the coolest to hottest location was approximately 110 DD.



Fig 1. Pear psylla degree day phenology model. Current nymber of accumulated degree days averaged among WA and OR as of May 6th 2021 (pink line).

What stage are psylla in now? There should be very few winterform adults still alive, and nearly all of the first generation eggs have hatched into nymphs. Warmer regions like southern Oregon are seeing mostly mid to late-stage nymphs and a few summerform adults starting to emerge. Cooler regions like the upper Wenatchee River Valley are seeing mainly early to mid-stage nymphs, and first summerform adults will start emerging in about 1-2 weeks.


IPM Recommendations: Just before summerform adults emerge (now, or in the next 2 weeks depending on your region) is a good time to apply a particle film like Surround (kaolin clay) or Celite (diatomaceous earth). These will deter the next generation of adults from entering your orchard and laying eggs. Once adults hit their peak (2 – 4 weeks), population suppression can be achieved conventionally with selective materials like Ultor (spirotetramat) or Esteem (pyriproxifen), or organically with materials like oil, azadirachtin products (not on Comice!), Cinnerate, or additional particle film sprays. Keep in mind, organic insecticides may require 2-3 applications on 1 week intervals.


These methods will have low impacts on natural enemies. Natural enemies like lady beetles (Fig. 2A), predatory bugs (Fig. 2B), and parasitoid wasps (Fig. 2C) are critical to prevent psylla population surges closer to harvest, and they do it for free! So avoid broad spectrum materials, especially multiple products at a time. Also remembr to do soft on codling moth. Use mating disruption and soft materials to control like oil, granulosus virus, Intrepid (methoxyfenozide), and Altacor (chlorantraniliprole).

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Fig 2. Natural enemies of pear psylla; i.e., your friends! A) Lady beetle feeding on psylla nymphs (L. Nottingham). B) Deraeocoris brevis feeding on psylla nymph (B. Higbee). C) Trechnities insidiosis parasitizing psylla nymph (R. Schmidt-Jeffris).

Funding: This project to develop recommendations corresponding to pear psylla’s phenology is being funded by the Fresh and Processed Pear Committees of Washington and Oregon and a WSDA Specialty Crop Block Grant.


Use pesticides with care. Apply them only to plants, animals, or sites listed on the labels. When mixing and applying pesticides, follow all label precautions to protect yourself and others around you. It is a violation of the law to disregard label directions. If pesticides are spilled on skin or clothing, remove clothing and wash skin thoroughly. Store pesticides in their original containers and keep them out of the reach of children, pets, and livestock.


YOU ARE REQUIRED BY LAW TO FOLLOW THE LABEL. It is a legal document. Always read the label before using any pesticide. You, the grower, are responsible for safe pesticide use. Trade (brand) names are provided for your reference only. No discrimination is intended, and other pesticides with the same active ingredient may be suitable. No endorsement is implied.



Louis Nottingham, PhD.

Research Assistant Professor

Dept. of Entomology articles may only be republished with prior author permission © Washington State University. Reprint articles with permission must include: Originally published by Washington State Tree Fruit Extension at and a link to the original article.

Washington State University