There is an invasive pest called the Emerald Ash Borer Beetle (EAB) that is killing ash trees across the country. It is a very serious threat and, over time, could kill most ash trees in North America if a cure/remedy is not discovered.
The EAB has been spotted in 13 states so far and is normally spread by the transport of undried firewood from county to county. There are some natural parasites that attack the EAB larva and are being cultivated in hopes that this can reduce the spread of the EAB, and the USDA is working to develop EAB-resistant strains of ash. It is unknown whether either of these remedies will be developed in time to stem the spread of the EAB.