Cedar Quince Rust

Well shut my mouth! When Jane Troup sent me a picture of her "alien invasion," I confidently diagnosed it and sent her this link to our cedar apple rust blog.  She responded, "It's weird though, no gall, just the rust." But I still didn't catch on.  Only when Linda Ellis sent another email to me and mentioned she had "never seen this erupting along the branches instead of just in galls" did the great light dawn.

Eruption on a cedar (Juniperus virginiana) branch - Dr. Dailey O'Brien, Bugwood.org

Cedar-quince rust doesn't produce the galls of the other cedar rusts.  Instead, the twigs and branches swell from infection.  Later they become elongated and the bark begins to peel.  Symptoms on junipers are described on the Missouri Botanical Garden site:

"Perennial, elongated swellings on the tips of twigs and branches, which may crack and form cankers, are symptoms of cedar quince rust on red cedars and other junipers. In damp spring weather, cushion-shaped, orange, gelatinous blisters burst through the bark where the branches are swollen. Cedar-quince rust disease damages the ornamental value of susceptible cedars and junipers, killing young branches and weakening plants when cankers occur on the main trunk."

Infected hawthorn fruit - MO Bot Garden

Much like cedar apple rust,which alternates with apples, this alternates annually between junipers and deciduous host trees.  In this case however it infects 480+ species of the Rosaceae family including serviceberry (Amelanchier), chokeberry (Aronia), hawthorn (Crataegus), and apple/crabapple.

My lesson from this is to listen closely to my botanical betters when they send me clues, instead of shooting from the hip directly into my foot.

* This University of Minnesota site,  describes the four varieties of cedar rusts.