There is some good information here:
You probably need to cut it down and remove roots. An herbicide may help since roots go everywhere.
Sumac is very sensitive to herbicides such as triclopyr (Garlon 3A and 4), so that existing stems can be killed by cutting and treating, or by basal bark treatment. However, although herbicide treatment will kill above-ground stems, rhizomes and the buds that turn into root suckers usually escape treatment.
Ranger pro works really well as it is a herbicide containing glyphosate as the active ingredient. . https://amzn.to/3gTu7Wr
Hope this Helps! Jeremy - https://pahjodesigns.com
Hi Theresa, sorry you are dealing with sumac trees. Hope this will help you get rid of them. How to Kill Poison Sumac Trees