From the Garden Gal podcast, published on June 3, 2013, here is a great tip that Debbie Cook received on how to spray RoundUp. RoundUp is a non-selective herbicide so it will kill anything that it gets on, which can be tricky in a full flower bed. Because it has to get on a green leaf to work, you have to be careful of overspray. Here is your solution.
Cut the bottom off of a 2-liter bottle (we used an half gallon orange juice bottle in this picture). Place the bottle over the top of the plant you are trying to kill. Spray inside the neck of the bottle.
The bottle will protect the plants around by containing the spray to what is inside the bottle.