Ash Tree Sudden Death, with Borer Holes
An ash in my neighborhood just suddenly died, leaves suddenly turned brown and fell off. When I inspected the tree I noticed borer holes and sawdust at the base of the tree. I did not notice anything wrong with this try prior to today. It is not in my yard, but I drive by it several times a day.
Jefferson County Colorado
This damage is from the lilac ash borer. This insect attacks stressed trees. If you look closely at the base of the tree, you'll see it has a sort of "pinched in" look. I suspect that the tree has a girdling root, which, over time, affects the movement of nutrients and water within the tree. It also appears to have been planted too deep. I think these combination of stresses are what led to the tree's demise. The insect is sort of the straw that broke the camel's back.
Here is a CSU fact sheet on borers affecting shade trees: