Black Knot

Dibotryon morbosum or Apiosporina morbosa is an infectious organism which causes black knot.

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It affects the cherry and plum trees of Canada.

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The disease produces rough, black areas which surround and kill the infested parts of the tree or shrub and provide habitat for insects.

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In the late nineteenth century, it was a very destructive disease for plums and cherries.

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These days, it is relatively well controlled though seen in poorly managed orchards. We see it frequently on choke cherry shrubs during our walks.

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Olive-green swellings can be seen in late spring. As it spreads and matures, the rough black knots circle and kill the affected parts.

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Older knots can kill trees by promoting insect infestations.

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These abnormal outgrowths 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.

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Pruning infected parts during winter and spraying buds with a fungicide are forms of treatment.

 

 

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Miles Hearn

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