If you look closely at the leaves of many trees, you may notice small bumps, irregular or spherical growth, velvety patches or other distorted growth. These different growths are called galls. They can look strange and unsightly but it is only a cosmetic problem and will not affect the health of the plant.
Galls generally form in the spring when an insect or mite lays eggs, feeds, or in some other way irritates actively growing plant tissue. The plant responds by producing a growth over the area that was irritated. You rarely need to control galls. Gall growths on leaves are unattractive and may cause concern, but damage to the tree is purely cosmetic. Because the tree’s health is not involved, homeowners need to determine if spraying is really necessary. Large trees are difficult to spray and you may need a professional to do a proper job of spraying. The number of galls will fluctuate from year to year and may disappear on their own. If you decide to spray, determine what causes the gall, proper treatment, and what product is most effective. For more information on galls contact your county Extension office, Master Gardener hotline or local nursery.