What is causing the unusual growth on the leaves of my maple tree? - Ask Extension
My maple tree has an unusual growth on the leaves this year. Is this something to worry about, and is there anything I can do at this point?
Knowledgebase
What is causing the unusual growth on the leaves of my maple tree? #205461
Asked August 08, 2014, 12:00 PM EDT
My maple tree has an unusual growth on the leaves this year. Is this something to worry about, and is there anything I can do at this point?
Washington County Minnesota
Expert Response
The round wart-like structures on the upper surface of your maple are maple bladder galls caused by a small Eriophyid mite, Vasates quadripedes (Shimer). The structures are often first noticed in May when the leaves have become fully expanded. The galls are initially green, but they quickly turn pink to red and eventually black. Leaves may become covered with so many galls that they completely twist out of shape and then drop early. These galls seldom harm the tree, so control measures are not generally needed. The following sites explain the life cycle of these mites.