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You may have noticed small lumps or long protrusions dangling from the leaves of your trees.  These are called leaf galls. Leaf galls can be hollow or hard, and look like there’s something wrong with your tree, but fret not.  These bumps are usually not a sign of disease.

While leaf galls look terrible, they are usually not anything to worry about.  The bumps are usually caused by an insect or bacteria feeding on your leaves. The bumps are an after effect, similar to a bug bite you may get.  The original organism is not still hanging around. Unfortunately, unlike our bug bites, leaf galls don’t go away.

Insects like to feed on new, fresh leaves, so leaf galls rarely affect more mature leaves on the trees.  You may also find galls on stems or flowers, but they are most commonly found on the leaves of trees, such as oaks, maples, and elms.  

Trees will most likely be more affected by galls after a harsh winter, when the bugs are hungrier.  This is usually not a problem for healthy trees, but trees that have encountered more damage over the winter season may be more susceptible to early leaf loss.

Since leaf galls are primarily a cosmetic issue, it’s best to just leave them alone.  If the insects are a problem, that typically takes care of itself, as gall causing bugs find natural predators rather quickly.  It’s also not a bad idea to spray your trees at the beginning of spring to ward off any unwanted pests.

With any unusual growth on your trees, keep an eye out for weakening trees along with the gall, as this could be a sign of something larger at play.  When in doubt, always call a professional arborist to examine your tree for further damage or infections.