Maple Tree Problem

I have a maple tree that I have been growing in my back yard for 3 years now. It is about 6 feet tall. About 1 in 3 leaves has a little red thing popping up out of it. I am not sure what it is. My question is what is it and if it is bad how do I fix it. Thanks
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These abnormal growths are leaf galls. While they may be aesthetically unattractive, they seldom result in harm to the tree so control is not warranted or necessary.
http://www.extension.umn.edu/distribution/horticulture/DG1009.html
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This is the time of the year we usually start seeing odd lumps or growths on maple leaves, which are called galls. This is simply a cosmetic issue and won't harm the leaves or tree. Enjoy this curiosity of nature! More info: http://www.uwex.edu/ces/wihort/gardenfacts/XHT1064.pdf
Suzy, Zone 5, Wisconsin

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