Help identify a pear pest
Thank you for attaching the excellent images. They reveal that your tree has Pear Trellis Rust, a disease which only recently was identified in Oregon.
At this time, information is limited other than that this rust fungus is passed back and forth between two different kinds of plants: Junipers and pears. Even though the pear leaves are infected during wet weather in spring, the obvious raised lesions don’t appear until late summer or early fall.
Management strategies are two. Collect and discard infected leaves. (Do not compost them.) And, if practical, remove all junipers from a 1000-ft radius. No chemical remedies are available for edible pears.
I will refer this to the university pathologist (plant disease specialist) who may contact you for further information. At a minimum, he will want to know the kind and name of the pear; the age of the tree, if known; if you have seen this problem on the tree in previous years; also, where you live in Multnomah County.
Not much more to add unless you want to respond. We could also ask questions about any Junipers in the area that may have trouble as well.
The juniper is thriving, but I've been thinking about getting rid of it for some time, and the association with the rust is added impetus to remove it. My hesitation is that it is very well established - it's been there for more than 3 decades - and I'm concerned that rooting it out might damage the roots of an oak tree that is on the slope just a few feet above where the juniper is. Also, I posted a NextDoor query about the leaves and heard back from a neighbor who lives at 4539 SW Pendleton who says that his ornamental pears have been plagued by this rust for the last 3 years. They are "scraggly and not doing well". He also has juniper about 30 feet from the pears.
Thank you for the information. It is not every juniper that is a host and some hosts are more resistant than others. Most folks do not know the species of Juniper which is why I did not ask about it. Unless you find a nursery tag it could be hard to determine the species. Take it out if you wish. It may not do a lot if there are other junipers nearby.