Pseudomonas syringae

This disease is the sneaky, quiet guy. A bacterium like fire blight, it affects a different group of hosts. Similar in its methods to fire blight, it attacks the rose family stone fruits that are immune to fire blight: cherries, plums, apricots.

When these trees are infected, usually one of the symptoms is gummosis, which is an amber-like deposition of hardened sap that collects near cankers. The other commonly affected hosts here are lilacs. They are affected with classic blight symptoms, wilted discoloured flowers and leaves.

One favourite tree that can be outright killed by Pseudomonas is the beautiful Amur cherry. Last year, a homeowner noticed some wilting on her 40-foot Amur in the McKenzie Towne area. Several calls went out, some time went by, and some misdiagnosis occurred. In about three weeks, the tree had gone from a couple of wilted looking branches to being overwhelmed by the disease. Removing it quickly to avoid spreading the disease was the only option.

(Photo credit: “Pseudomonas syringae on Syringa vulgaris (location: Poland)” by Jerzy Opioła, licensed under CC BY-SA 4.0.)