Industry News: Bark and Trunk Concerns

Q: Cherry tree has strange-looking clumps on the branches and trunk that grow and fall. What is it?

Thursday, December 31, 2015  

A: It has two things going on: one is a fungal disease called Black knot; the other is a curious, abnormal growth called witch's broom. Black knot is fairly common on cherries and usually is indicative of poor growing conditions. That covers many possibilities, from poorly drained soils to fertility issues. Wen one is growing cherries for a fruit crop, it means the tree is not vigorous and probably will not produce much. If it's being grown for flowers, it may well continue to perform for years. Some plant pathologists say you can control black knot by pruning it out and applying fungicidal sprays. Others say spraying is not effective, but pruning out the black knot galls is helpful.

Witch's brooms are clusters of twiggy growth that are caused by various microscopic organisms, and are not well understood. A number of landscape plants have been developed from this sort of mutation, which results from a hormonal imbalance that the causal organism initiates. One you may be aware of is dwarf Alberta spruce, which was propagated many years ago from a witch's broom on a full-size Alberta spruce. I would not worry about the Witch's broom, but you can prune them out if you want. The black knot may eventually overwhelm the tree. All in all, I would say to enjoy the tree as long as it provides what you want. That may be flowers, or it may be as a conversation piece regarding the witch's broom! Good luck with your tree.

Responder: Ed Milhous, RCA #350, Haymarket, VA