What can I do next to a dying ash tree?
Answers: Was the borer a green color? If it was, report it to your local county extension office at once, as it would be the Emerald ash borer, explicitly killing thousands of ash trees. If you are in the Michigan, Illinois, Indiana or Ohio nouns, or anywhere near there, it is drastically important you report it and get the tree removed now.
Do you know why it is dying? Is it insects and if so can they be treated?
Is it disease? Is it a treatable disease?
Is it a structural problem such as a compromised root system? Not much can help there.
Is is weather related? Lightning?
First you call for to know WHY it is dying? The best source is a certified arborist accredited with ISA or NAA...it will speak in their phone book ad. Yes, they will charge to come and diagnose. You pay cheque a doctor, these arborists are tree doctors, they know their stuff. They may recommend treatment and pruning. If you own a tree, it cost money to maintain them.
Second thought would be to call your Cooperative Extension Service agent. They may own a Master Gardener program where you can bring in tree sample or maybe the MG will come to your yard. Realize MGs are not arborists! They may be capable of diagnose insect problems, maybe cultural problems and offer suggestions, but they can not do the work.
You requirement to call in professional support. In the mean time think going on for what has happened to the tree surrounded by the last few years: has within been construction near the tree, have the soil level changed, drainage patterns, what chemicals hold been used under or hard by the tree both in your yard and I don`t know neighbors, has the tree been hit by lightning, previous pruning can definately interfere with trees if done incorrectly, etc.
Without me seeing the tree I can't tell if it has ash borers, girdling root or herbicide wreck...all three possible causes.plus a dozen more.