Sick spring flurry Serviceberry from friends of trees

Asked May 21, 2018, 6:45 PM EDT

I planted a spring flurry serviceberry this spring in my parking strip and now it looks spotty and sick. I attached some photos. Any thoughts on what is going on and how to treat it? Thanks, Anna

Multnomah County Oregon

1 Response

What you have is called Pear Cedar Rust, aka Pacific Coast Pear Rust, aka Cedar Broom Rust. Or, scientifically, Gymnosporangium libocedri. It has so many names because it has an interesting story....

This fungus bounces between Incense Cedar trees and members of the rose family --most commonly pears, but also, when conditions are right, apples, quince, wild roses--and closely related plants like hawthorn, mountain ash, and serviceberry. It lives on a cedar tree for three years, and then forms a sporing body that looks like a mass of orange jelly thrown up into the tree. Those spores do not reinfect a cedar tree, they must find one of those alternate Rosaceous hosts. When it infects one of those, it forms those bright yellow / orange raised bumps which you are seeing. These are also sporing bodies, producing spores that will not reinfect any member of the rose family hosts, but must find an incense cedar to infect.

The most effective treatment is to locate the incense cedar(s) that must be fairly close to your yard (but very possibly in a neighbor's yard), and either remove the tree or cut out the bright orange sporing masses when they appear. Alternatively, especially if the incense cedars are large and beautiful, remove the serviceberry bush! There is no effective fungicide available for the homeowner to use on the cedar host. Immunox will work on the serviceberry or pear phase, but it will render any of this year's fruit poisonous. NEVER eat any fruit from a tree or shrub that has been treated with Immunox in the preceding 12 months! (As always, carefully read and follow the instructions on the label when using any pesticide.)

Note that this interesting rust is much more common on years when we have unusually warm wet springs; in ordinary years it is fairly rare. With near-90 degree days in both April and May, this year we are seeing lots of it!

Here is a link to an article by Denise Ruttan and Jay Pscheidt, a plant pathologist at OSU: http://extension.oregonstate.edu/gardening/watch-out-rust-can-jump-incense-cedars-fruit-trees