Ash Tree Problems
Your ash is dying. Emerald Ash Borer is an invasive pest that is killing Ash trees in our state and others.
Here is our page about it. http://extension.umd.edu/hgic/invasives/emerald-ash-borer
If less than 30% of the tree is affected, you could have an arborist treat it, but it would need to be continued indefinitely.
If you don't treat, and it's fall would threaten people or property, have it removed sooner rather than later, as they become weak very quickly, to the point that some tree companies won't climb them or consider them 'hazards'.
I don't see evidence of a borer. Could it be something else?
You probably would not see the actual holes of the emerald ash borers. Please read through the info above so you know what the symptoms look like.
Anthracnose is a fungal disease which will also make ash leaves curl and drop, but they don't usually turn brown before they drop.
Or your tree could be dying for other reasons which we have no way of determining.
Please have an arborist look at your tree or else send us photos if you still do not feel you know what is happening to your tree. For an arborist certified by the International Society of Arboriculture (which is who we recommend) near you, follow the prompts on the following website: www.treesaregood.org
If you choose to send us photos, send us several showing affected leaves that have not turned completely brown. Close and far shots.