Question
One of my mother -in -law's maple tree (in mn)has slightly raised red bumps on the back side of all the leaves on one maple & the other tree has none. they have an oak tree in between them. what is this & why one & not the other  tks

Answer
Larry:
Not sure, but these bumps may be an insect. If the tree is well established and looks good, I suspect these critters don't have a significant impact on the trees well-being.  You can collect a few of these leaves and carry them by your local county Extension office for an ID.  Doesn't sound like a disease, but it may be an insect gall of sorts- there are a bunch of different kinds out there.  Another option--in the meantime,take a closeup photo and email to me and I will have a look. Be sure to review it and make sure it is in focus Before you hit the send button.
Steve