There are thousands of types of galls produced on a variety of trees, including Maples, Oaks, Hackberry and Spruce.95% of galls are formed by different parasitic insects, usually microscopic or very small in size. Galls develop when the plant tissue is irritated. It’s believed that the parasitic insect produces a plant-growth-regulating chemical that deforms the leaf surface and causes the gall to form.

Maple Bladder Gall is one of the most common galls in Illinois. Silver Maples, in particular, are prone to Maple Bladder Gall formation, but other Maple varieties are also affected. The Maple Bladder Gall is caused by a mite insect that is feeding on the leaf. The mite is so small that it may require a hand lens to view. The leaf swells in the area where the mite feeds, comparable to a mosquito bite on a person. The leaf swelling is caused by the irritation and toxins put into the leaf by the mite insect.

Maple Bladder Gall starts as yellow or red bumps on the leaf surface and turns brown as the year progresses. It may be unsightly, but Maple Bladder Gall doesn’t cause much harm to the tree. The galls that appear are actually leaf tissue, and not the mite insect, which has finished feasting on the tree.

Have questions or concerns? Call the PHC Department at KTS!

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