Removal of ash tree
The tree was mature when we bought the house 42 years ago. When I had a tree company come to check and trim the tree this spring I was told that it was infested with emerald ash borers. Foliage at the top of the tree has thinned out. The tree gets quite a bit of sun because it is taller than the house, 40 or 45 feet. The soil is typical Maryland clay. It has not been fertilized itself. The grass gets an application of fertilizer in the Spring. Is there an effective treatment? If not, is there a law about removing the tree, either state or county?
Emerald Ash Borer is an invasive species which is killing ash all over Maryland. Here is our page on EAB: http://extension.umd.edu/hgic/invasives/emerald-ash-borer
Whether emerald ash borer is treatable depends on how much of the canopy is already involved. If more than 30-50% is thinning, it is too late. It is also something that would need to be repeated over time.
Here is a page that helps you decide whether you (or a professional depending on size) can consider treating: https://extension.entm.purdue.edu/EAB/PDF/NABB_DecisionGuide.pdf
We are not aware of any laws regarding EAB tree removal specifically, but you should act sooner rather than later to remove if it's fall would threaten people or property. These trees loose their structural integrity pretty quickly. Some arborists or tree companies either refuse to climb them or add hazard fees because the wood weakens so quickly.