About this Webpage
This webpage outlines season-long integrated pest management (IPM) program guidelines for pear. The guidelines a built around a degree day model that predicts the development of pear psylla life stages and generations. The guidelines in this page (above) place specific strategies at timings where they can affect vulnerable life stages while minimizing harm to natural enemies. Most sprays target adults and eggs. Sprays are less effective on pear psylla nymphs, which are better suppressed by natural enemies (for example, the parasitoid of pear psylla, Trechnites insidiosis, only attacks nymphs, not eggs or adults). Further, thresholds help to avoid unnecessary sprays when pest populations are too low for concern. Timings for non-chemical tactics, such as tree washing and pruning for pear psylla and mating disruption for codling moth, further support this goal. Altogether, this program supports effective pest management while reducing input costs and enabling biocontrol.
Insect development rates depend on temperature. After making observations and using them to build mathematical models, we can predict the relative abundance of a pest’s life stages across its generations within a season based on accumulated temperature units called degree-days. This degree-day phenology model for pear psylla was developed by Vince Jones of WSU in 2019. Learn more about degree-day models and how they are made on the Degree Day page.
Biocontrol and Natural Enemies
The term “biocontrol” means suppression of pest organisms by other living organisms. We also use the term “natural enemies”, referring to the naturally occurring predators or parasitoids that kill pear psylla or mites (therefore, providing biocontrol). More information on natural enemies in pear orchards can be found Pear IPM Natural Enemies page.
How These Guidelines Work Alongside Biological Control
The management guidelines on this page work by conserving natural enemies while suppressing pear psylla. This approach results in less pear psylla pressure later in the season (both before and after harvest) because of the natural enemy populations you will cultivate. Programs that use multiple broad-spectrum insecticides, on the other hand, may appear to control pests early in the season, then lead to pest outbreaks in mid-summer. When using the phenology-based guidelines on this page, you may find pear psylla adults, eggs, or nymphs at higher levels than were common in the broad-spectrum insecticide programs. However, the chance for injury will be much lower because predators and parasitoids are present. So, try not to abandon the program if you see some psylla – remember, psylla are predator food! Allowing natural enemies to build through the season will control psylla populations in the fall, resulting in fewer psylla the following year. Natural enemies cannot perform this service if multiple broad-spectrum insecticides are used. Try to limit yourself to no more than one broad-spectrum spray per season, preferably prebloom at 200 PDD, and only if pear psylla pressure is high. If you do make one broad spectrum spray, natural enemies can recover, so do not abandon the overall selective approach.