Trees in decline have an unhealthy look. Often, leaves are fewer than normal and overall growth has been poor all season. Leaves may have yellow or brown tips or may be smaller than normal. Or there may be premature fall color and early leaf drop.
Tree decline never happens overnight; it can come as a result of a single disease or environmental factor or, more commonly, from stress over many years. Often, there is more than one stress affecting the tree. Stressed trees are often predisposed to other problems, such as boring insects and injury from extreme weather.