Q.I Thought Lilac Bushes Lasted Forever, But The Bush Clump That Was Here (well Established) When We Moved In 40 Years Ago Started S
howing signs of shelf like fungus growth followed by dying branches. This year the old original trunks were rotted and could be p ulled out of the ground. Is this a normal life cycle type of thing? There is an 8 foot volunteer black walnut which I keep cutting off and can;t seem to kill in close proximity to the lilac. Some one told me that the toxic root could be killing the lilac. So I guess it’s a two fold problem? Thank you.

Certified GKH Gardening Expert
The Walnut certainly did not help, but if you are seeing shelf mushrooms- They are the culprit. Most shelf mushrooms will damage heartwood, and some will damage sap wood. Both will kill a tree over a span of time, with some exceptions.
Your photo did not come through, so I can't ID the fungus. I can say that you will want to treat the area with a fungicide before planting anything in that area, again. It could fall to the same fate.
This article will help you with fungicide use:
https://www.gardeningknowhow.com/garden-how-to/info/homemade-fungicide.htm
https://www.gardeningknowhow.com/special/organic/biofungicide-information.htm
https://www.gardeningknowhow.com/garden-how-to/info/using-fungicides-in-garden.htm