Glyphosate has worked for me on poison ivy too. Of course what few people state is what concentration they used. For general broadleaf weeds, grass, etc, 3% or 4% works fine. If I was doing a bunch of PI or similar, I'd use 6%. But if I had a tank of lower concentrate, I'd just use that on some small plants like the OP has. Worst case, maybe you have to hit it twice. And if you have a lot of tougher stuff like that, then one of the other brush killer products is better yet.