Ask Mr. Smarty Plants

In order to find a point of reference, we found three members of the Rhus genus native to Central Texas: Rhus aromatica (fragrant sumac), Rhus glabra (smooth sumac), and Rhus virens (evergreen sumac). You probably have, at the very least, some of all three of these plus others that have migrated in. The bad news, in your case, is that this is a very tough survivor. It can take just about all soils, rocky, sandy, limestone, etc., is drought resistant, can thrive in sun, part shade or shade. But the worst news is that it spreads by suckering. Colonies are often single-sexed, formed from a single suckering parent. Worse, we learned that colonies can be rejuvenated every few years by cutting them to the ground in mid-winter, which is probably what happened to you when you tried to cut them back in cool weather. 

Sumac is generally so well-regarded that we could find no references to how to get rid of it.  So, we are going to offer some ideas for you to try. You obviously already know that it comes back with a bang when it is cut down. However, it would seem from the information on rejuvenating it by cutting down in the winter also suggests that cutting it back in the heat of summer might have the reverse effect. Because the Rhus genus has suckering, spreading roots, cutting off one area of the shrub just means the upper part of the plant will have to go to another area for nutrition. But, any plant can be eventually starved to death, and being cut in the dry hot summer would hopefully discourage it. You can hardly dig out all those roots. As the plant digs in for survival, it will continue to pop out more suckers. So, our first suggestion is to keep cutting, perhaps even mowing, and do it into the heat on the summer. Hard on the gardener, but hopefully harder on the plant.

A second line of control is the use of an herbicide. The Lady Bird Johnson Wildflower Center recommends neither for nor against the use of herbicides and pesticides, but in this case carefully controlled use may be necessary. Don't spray, you are dealing with too large an area, and spray can easily drift onto more desirable plants, contaminate the soil, and get into the drainage off the area. Instead, with large heavy-duty clippers, cut off main stems at the ground, and immediately paint the stub with an herbicide. This can be done with a disposable paintbrush, and must be done within 5 minutes of cutting, before the stub can seal itself off. This will then permit the herbicide to penetrate into the root system. That system is probably so extensive that applications everywhere you can find a stem to cut and treat will be necessary.

This is not a quick fix, and is going to be tedious. The plant will probably keep trying to return, since it obviously finds your area very enticing. Wild animals and birds who browse sumac or feed on its seeds will carry fresh seeds onto your property; again, frequent mowing is your best way to control the return of the plant.

Rhus aromatica

Rhus glabra

Rhus virens