Black Knot

Snow White Black Knot

I planted a multi-stemmed Canada red chokecherry (Prunus virginiana 'Shubert') years ago in my landscaping so I could admire the deep, purplish-red foliage; a signature display of this selection.  Of course, that was before anyone knew it’s a magnet for the fungus, Apiosporina morbosa; the plant pathogen that causes black knot.  The disease is characterized by thick, corky, elongated gall-growths on twigs and branches that become coal-black late in the growing season; thus the common name for the disease.  Black knot is now the signature display of many Canada red...

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Authors
Joe Boggs

Black Knot Not Black

Black Knot of Prunus is caused by the fungus, Apiosporina morbosa, and is characterized by thick, corky, elongated gall-growths on twigs and branches.  The common name of the disease is based on the coal-black coloration of older galls late in the growing season. Currently, newly sporulating black knot galls are olive-green or reddish brown and may have a velvety texture.  Newly forming galls may appear as simple swollen growths causing the bark to crack; they may be mistaken for a cankering disease.
Published on
Authors
Joe Boggs