In The Garden – What is Black Knot?

By Jan Dugdale – LaSalle Horticultural Society

Photo courtesy of
Taken by Tricia Simon

Black knight is a fungal disease of plants in the Prunus Genus of the Rose family. Other plants besides the Chokecherry are cherries, plums, mayday, and apricot that may be at risk.

If you see long black knots that look like goose poo it’s how the disease is characterized. The knots and compass twigs and small branches but can show on the leader branches and trunk.

This fungus spreads by releasing spores after warm wet weather. When, rain, insects and animals also spread these spores to other trees infecting them.

Once established the disease gets worse with the growth above the not becomes stunted and eventually dies back when the disease enters the leaders and trunk death is imminent.

There is a fungus side for black not but it is very expensive, so the best control option is to physically remove. Removal should be done during the disease is norm dormant season, so late fall through to the early spring. The lack of leaves at this time allows you to see the knots for removal making it easier.

To avoid further spread you can cut at least 15 to 20 centimeters, 8 6 to 8 inches below the knot. Ensuring the removal of all internal infection. If you’re not as in a bad location, cut back to healthy tissue at least half an inch past the not.

Black knot can spread quickly so all you’re cutting blades should be disinfected after each cut. Disinfect with propylene alcohol. For this disease, know your three “B’s”, bag it, bury it, or burn it. Any of the diseases would release the scores for remembering the three B’s.

Bagging is not needed when your tree is dormant however if remove all of the knots during the effective growing season, bagging is important if you can’t burn or burn it and greatly reduces the spread of this disease.

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