How do you kill off Sumac Trees. We cut 2 trees down and they are now

come back with herbicide for 'woody' growth plants; you'll have to treat as new growth appears - or grub out the stumps/root system.

Quick fix is to hire a stump grinding service - can be expensive. Or drill holes in stumps and repeatedly drown in vinegar. Will eventually rot out. To speed up the process, purchase "agricultural vinegar" which has a higher acidity content.

Your question got cut off, but I assume that you are saying they are coming back. I assume you did not dig up the roots so they are sending up new shoots. Cut the new shoots off somewhat close to the ground. Use a good weed killer and PAINT the cut end with it. If it is real tenacious, it may take a few times for the killer to get all the roots to die, just trim again and paint on the cut end until it does not come back. It took me nearly a year to get rid of a wild grape that was huge, but trying to kill a massive lilac my neighbor has by our driveway, it was even trying to grow under her siding. It has been three years now and it still hasn't come back! Be patient and you will kill the offending roots, they can be real hardy. By painting it on, you will not affect the grass, soil or any other nearby plants that inevitable get hit with over spray from weed killers. It will eventually absorb enough into all the roots to stay dead.

Watering with bleach for a couple weeks. After, water for a week to wash bleach away before replanting.