RoundUp QuikPro is not labeled to control catbrier. Catbrier or Smilax is very difficult to control and usually requires a combination of digging and possibly mutiple herbicide applications over several years to eradicate the root system completely. The only product we have labeled for this plant is TVC Total Vegetation Killer. This product stay in the ground for up to one year, so you would only want to use it in areas where you don’t have or want any desirable plants for at least this long.
This blog post has some great accounts of treating this plant. And this guide from the UGA Extension has some great insight, too. We always recommend contacting your local Cooperative Extension for further assistance with tough weeds like this one in your area.
