Black Knot is a fungal disease that causes infected plants to develop black tarlike swellings. The disease affects a wide variety of trees of the prunus species including, but not limited to plums, cherries and apricots. The disease is also very aggressive in Mayday and Chokecherry trees.
A recent survey in Alberta revealed a significant and widespread distribution of Black Knot found in commercial, municipal, private and natural plantings. This disease reduces the aesthetic value of affected specimens, as infections spread rapidly; high levels may result in the eventual death of the plant.
Black Knot is distinguished by the black, tar-like swellings that develop on the branches of the infected plant or tree.
Initially, a small, olive-green gall or swelling will develop at a succulent growing point or fruit spur (as a result of spores landing and infection taking place). This swelling will grow until it is mature after 2-3 years. The mature galls are hard, black, 10 to 15 cm (4 to 6 inches) and may be somewhat ruptured. Mature galls will produce and release a vast amount of spores during the bloom period, resulting in a rapid increase in infections. The fungus continues to grow internally and externally, with the branch eventually becoming girdled and dying.
Each year, Devon’s Parks department spends over 100 hours of labour pruning trees deemed “at risk” for developing Black Knot. Over the past few years, all of the seriously infected trees across Devon have been removed and replaced with a different tree with a much lower risk of being infected by Black Knot.
Contact Devon's Parks department with any questions regarding Black Knot at 780-987-8316.
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Municipal Office Contact
Town of Devon Municipal Office
1 Columbia Avenue West
Devon, AB T9G 1A1
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