It probably won't work on marestail and I wouldn't spray glyphosate anywhere to avoid drift use a watering can and a fine rose (and only uise them for weedkiller, it's what red cans are for :D).. for marestail the problem is the skin of the thing is pretty much impervious.... you might need to get a metal pot scourer, mix up the glyphosate with some wall-paper paste, scrub it into the marestail then put a clear plastic bag over it.... sounds extreme, but I see it bouncing back year after year on areas I know are regualrly hit with roundup...... You might find it more effect to use the brushkiller/stump kliller varieties of glyphosate too, they're stronger.....
chrisc
