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Dealing with Leaf Galls

What Are Those Bumps on Your Tree's Leaves?

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A Type of Spindle Gall

A Type of Spindle Gall

Marie Iannotti Leaf Gall Photo

Leaf Gall Photo

Marie Iannotti

Have you ever picked up a leave that was dotted with bumps or had long protrusions dangling from it? Chances are these are galls.

Leaf galls are a frightening sight, but are not usually as serious as they appear. These bumps and deformities are usually the result of insects or mites feeding on the leaves. The gall itself is the plant’s response to the irritation. It’s not unlike the bump you get when an insect feeds on you, expect the leaf gall is not going to go away.

Despite appearances, the insect is not living in the gall. In fact, it is very likely that once you notice the galls the insects have moved on. Before they do, they can do a lot of cosmetic damage to many plants and in particular trees. Many common trees are susceptible to leaf galls, especially in the spring. Maple, oak, elm, hackberry and others each are favored by a different insect that causes unsightly and intimidating galls. Damage will be greater following a mild winter, since more insects have survived and are hungry. Galls won’t usually kill a tree, but they may cause early leaf drop. A healthy tree will send out new growth and recover.

What Can You Do About Galls?

Since the damage occurred before the gall formed, treatment is rarely recommended. If you have a serous reoccurring problems, you can spray your tree in early spring, to lessen the severity of the damage. Contact your local extension office for specific guidelines and recommendations in your area. But if you're patient, nature may take care of the problem for you. Gall making insects tend to attract their own predators.

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