Nature’s Note: Ash Flower Galls common this winter

This winter many urban ash trees are covered with unusual growths called ash staminate flower gall.

An infected tree's twigs are covered with crumbly brown or black growths that look like flowers. Even when driving by it is easy to spot gall covered trees.

Because of the growths, anyone can distinguish the tree's gender. Ash trees are dioecious, which simply means that an individual tree is either male or female. If it has galls it is a boy tree.

The infection is particularly common in trees planted in urban or suburban lots, because people dislike raking up seeds that fall from female ashes. Nurseries sold male 'seedless trees” to eliminate yard clean up. As a result, a high percent of urban and suburban trees are infected male trees.

A tiny mite overwinters in male oak flower buds. In the spring it feeds on flower buds, causing the tree to create the gall. During the growing season the gall is green, but in fall it hardens, turns black or brown and stays on twigs all winter.

Unlike the unrelated Emerald Ash Borer, which devastates ashes, the tiny mite that causes the gall does not harm the tree and there is no need to treat it.