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Bumps on Maple Tree Leaves

Q: I have several Maple trees on my property, on some of them there are these red nubs growing on the leaves.

It is occurring on both Red Maples & Silver Maples. What is this?

I have attached a picture of a Red Maple leaf with these growths.

Maple Leaf with red bumps on it

A: What you are seeing is a curiosity of Nature called maple bladder gall, and is often found on silver and red maples.

The bumps, which are mutated leaf tissue, are caused by the feeding of a tiny mite. The mites hide on the tree over winter, emerging in spring to begin their work.

The bumps are usually green to begin with and are hard to notice at this stage. They then turn pink or red, and finally black. Sometimes they'll cover an entire leaf and it'll distort and fall off early.

However, these galls rarely, if ever, cause any true damage to the tree, and control is usually not warranted.

Once you see the galls, it's pretty much too late to try to control them anyway, so it's a good thing they're not a threat to the tree. Other than the aesthetics of having some bumpy leaves, there is no harm done.

Suffice to say, you shouldn't really worry about the bumps. Instead, sit back and enjoy one of Nature's oddities.

p.s. Thanks for sending a photo!

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Tom Mugridge

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