You might want to keep some of those suckers in case it is dying. I don't know what's wrong with it, but it's trying to survive with the suckers.

need a pic ...

obviously the root system is not dying ... if it grew a 5 foot sucker ...

whens the last time it was rejuvenation pruned???

is your grass sprayed with lawn chems??? or did you dump any product on it in spring???? or late last fall ????

might also help to know where you are ...

ken

Going on what sounds like a soil pathogen, I googled for Sumac soil pathogens and Verticillium Wilt came up.

There are photos and reading about it, here.

Dax

I consider any one stem of sumac to be very temporary. In nature, it is a thicket-forming plant with numerous stems. Any individual stem is of no great consequence. The colony is what survives. As such, I'd rank as unwise any heroic efforts to save "this tree". In fact, if it were mine, I'd give serious consideration to cutting it down flush with the ground, thereby ensuring multiple root suckers next year. From these, you could select one and continuously cut back all others to try and develop a "sumac tree" again. And again, this could work for a while but ultimately would fail. Such is simply the nature of sumac.

+oM