Years ago I cut down a small, wild cherry tree in the backyard. I noticed it had strange black lumps on some of its branches. It took a long time before I noticed those same odd lumps on my Methley plum. It took even longer before I got around to finding out what those lumps were.

My Methley was pruned a few weeks ago. It looks ok from a distance although it resembles a flailing octopus.

This is a close up of one diseased branch.

And another.

Underneath the white goo, the bark is swollen, black and hard. Now and then large chunks of disgusting goo fall off for the unwary to step in. I can prune the smaller branches to get rid of the disease, but not major limbs.

This is one of the small branches I cut off. The disease is called Black Knot for obvious reasons.  It’s a disease specific to plum and cherry trees and a few others. The gray on the surface of the black stuff is a secondary fungus.

Black Knot is caused by the fungus Apiosporina morbosa. The fungus overwinters in knots on twigs and branches or in the infected wood. The fungus spreads by ejecting spores into the air during rainy periods to be blown by the wind.

I considered spraying a fungicide, but decided not to. I simply waited too long. Although the Methley is a sturdy, robust tree, it will eventually weaken and die from the infection. My biggest concern is that the disease will spread to the cherry trees in the yard and the little Santa Rosa plum planted next to it.

It’ll be removed next winter. I won’t miss the plums because I rarely got any. The blooms were nearly always killed by a late frost.

I’m considering replacing it with a dwarf weeping mulberry.  It’s a vigorous grower, fairly disease-free, tolerant of clay soil, adaptable and does not resemble a flailing octopus. Best of all, I’ll get some fruit!

This is a lovely picture of one from

Check out Six on Saturday’s head gardener and links to gardens around the world at Six on Saturday 02-02-2019.