It's hard to tell you how rich of a mixture to make because it's dependent on factors like how coarse or fine your spray is and how fast you drive.

I can tell you that a 1% mixture of gly will kill most weeds if you condition the water with ammonium sulfate so that you're getting the most out of the gly. I have calibrated our sprayer at camp to spraye about 12-13 gallons per acre with 1% gly and we get a good kill. I'm using a boom sprayer with size .02 nozzles so I'm spraying and fairly fine mist which yields really good coverage.