What is causing my maple tree to lose its leaves?
My 10-year-old maple tree has been losing leaves from the center of the tree out. The attached picture is a good leaf on the left and two diseased leaves - center and right. Do not see bugs, scale, or aphids. Almost looks like leaves are turning fall color, but orange is more like dull rust. Is it a fungus wilt?
Dakota County Minnesota
Many things can account for the symptoms you have described. Some of them are described in this publication: Maple Decline: Various Factors
Asking a forester or certified arborist to assess the tree's health onsite is probably the best way to determine what's causing the problem.
In the meantime, see if you can rule out verticillium as a possible cause by reading the following publications. Norway maples are especially susceptible to this disease.