Black Knot

Black knot is considered a gall and is easily identified by its rough black appearance. The black galls are most noticeable in fall or winter when leaves are not prevalent. The galls usually form along branches but can also be found along the trunk of the tree. Spores are spread through spring & summer, and initial/ recurring infections will also occur at this time. Green spores will be apparent along the edges of old and new galls. In late summer galls will turn black and hard. The Black Knot fungus overwinters inside the galls, then restarts the cycle again in spring.

Control Methods

Black knot primarily affects the Prunus genus which includes: plum trees, cherry trees, and chokecherry trees. The main control for this disease is to prune off affected branches. It is imperative to sterilize pruning tools in-between each cut to prevent further spread of the fungus. Pruning during the dormant period of both the tree and fungus (ex. late fall – early spring) will allow for the best results and will prevent the least amount spread.

Disposal

Do not put infected branches that have been removed in your personal compost or in municipal green waste facilities. Put branches in a black garbage bag or other sealed bag and put in your garbage bin for pick up or take to a local garbage disposal.