Black tree Fungus or mold?

Asked May 16, 2018, 9:49 PM EDT

I have 4 cherry trees that have some sort of black fungus or mold growing on the branches. It grows 6-8 inches long and surrounds the branch until it eventually kills it off, on the larger branches it appears to be eating through them. I’ve tried cutting out as much of the fungus/ mold as possible but it comes back worse each year. Is there anything I can do to save my trees?

Wright County Minnesota black knot cherry trees prunus

1 Response

The black stuff is a fungus called Black Knot, which is unfortunately really common in the Prunus species., which includes cherries. It effects wild and cultivates Prunus species, so it can be challenging to control.

Some trees it just be cosmetic, but it can also kill a tree - the effect that the fungus has on trees can vary widely between species of tree. The fungus does not systematically infect the tree, rather infects the branches at and around the gall (the black stuff). Prune those branches out, removing at least 4 inches of healthy appearing wood around the gall. Ideally you want to do this in early spring before the fungus has a chance to spread it's spores.

Fungicides are really only effective on young trees and and new growth. Any fungicides should be applied in early spring as well. I will include links below that has suggested fungicides. Be advised to read all instructions provided on the product and follow carefully.

https://www.extension.umn.edu/garden/yard-garden/trees-shrubs/black-knot/
http://blog-yard-garden-news.extension.umn.edu/2011/02/black-knot-of-plums-cherries-and-other.html