witches’ broom

A witches’ broom is a dense ball of short congested twigs growing from one point on a branch, standing out from the normal structure of the tree like a nest. It is caused by fungi, mites, viruses, bacteria, or mistletoe interfering with the growth hormones at a bud, so the tree keeps producing shoots where it should have produced one. Birch, cherry, spruce, and hackberry carry them commonly.