If you have a sliver or red maple tree, you’ve most likely noticed small raised bumps on the leaves. Tree owners will call them “freckles”, “measles” and sometimes even “zits”. Whatever they are called, maple bladder galls are caused by a very tiny mite. The galls themselves are made up of plant tissue and are a part of the leaf. Maple bladder gall mites live, eat and mate inside the galls and are well-protected from any application of a miticide.
Are the mites harmful to the tree? Most assuredly they are not. Occasionally there may be so many galls on one leaf that the weight of the galls themselves will cause the leaf to fall from the tree. Few leaves will be affected to this extent and leaf loss is inconsequential.
Galls will be a pinkish-red color and, as the season progresses, will turn light green and finally black by season’s end. While these leaf blemishes may be alarming to tree owners, the bumps are only cosmetic and treatment is not needed.
More information about maple bladder galls may be found here: https://ag.purdue.edu/btny/ppdl/Pages/POTW_old/7-7-08.html