Last year my husband and I had a hard time keeping weeds at bay, so this spring I discussed options with one of our herbicide sales reps; he suggested using the Killzall 365. In the past we have used Eraser (generic round-up) and have had to spray every few weeks (since it is exclusively a contact killer). The Killzall 365 is meant to be sprayed once a year- it kills all growing weeds and future weeds. I added about 1/4 of the bottle to a 2 gallon pump sprayer.
The picture to the right shows part of our driveway about 2 months after I sprayed it >>
It seems to be working!
<<<The picture to the left shows 4 days after spraying the edges/middle of the driveway.
If mixed strong enough Killall 365 can kill trees (and we're pro-tree at our house). It has a drip line of 2 (1 drip line=distance from the trunk of the tree to the edge of the branches).
I use Eraser Foam on the edge of my flower bed and near tree lines. It doesn't go very far but I prefer not to have to store multiple sprayers.