Black Knot

I received more than one comment or email on my Foam in the Creeks post which armed readers with information that could make them nature Smarty Pants when hiking with friends…

Well, here’s another one that may help you when someone asks, “What is that black stuff on the branches of that tree?”


The black, warty galls appear on trees in the Prunus genus. In this case it is Black Cherry (Prunus serotina), but it often affects wild and cultivated prune and plum trees as well.  Because all these trees have commercial value, you can find plenty of information about Black Knot (Apiosporina morbosa) and how to control it online!

The Cornell site listed below includes this diagram explaining the “disease cycle” of Black Knot:

While there are fungicidal treatments that can be used, most of the articles first recommend pruning in winter and removal from the site and/or burning of the galls.

Img_01Michael Kuo, author of many of the articles at, has a great sense of humor.  First, he describes Black Knot as looking like “dried cat poop on a stick.”  Each article at the Mushroom Expert site includes information about whether or not the species is edible.  Regarding Black Knot, he had this to say:

As far as the edibility of Apiosporina morbosa is concerned, I have four words for you: Look at the picture.

He cracks me up.


3 thoughts on “Black Knot

  1. I remember seeing something similar on a eucalyptus tree in our Australian back yard. Thought it to be of the nature you are describing, when it started to writhe, caterpillars entwined enmass – like an alien life-form. You probably know the caterpillar formations I’m talking about. I much prefer your cat poop Black Knot any day.

  2. Pingback: Gummosis « A Passion for Nature

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