Mix in regular lawn dandelion killer (something with 2,4-D or Trimec) with your roundup. Soak the heck out of your targeted weeds with a hand sprayer, that will kill almost any plant alive and it is a cheap mix. If you have the cash, buy a gallon of dicamba from a local ag supply store. I have found that the glyphosate and dicamba mixture is better, but certainly more expensive.