Interesting idea. One of the reasons some people are leery of chemicals is the potential for runoff. If you douse an area with urea, you will certainly have at least some nitrogen run off. I would be surprised if it killed all the weeds, there is sure to be something that would survive the onslaught.

I don't think you would have to use much if it's a foliar application. I suspect 10-12 ounces of urea per thousand along with a surfactant would burn the heck out of everything it touches. It might take less than that, testing would be needed to find the best rate. Potential for runoff would be minimal, we routinely apply 1 pound of N (32 oz of urea) per thousand monthly as fertilizer. I think at least 30% would be lost through volatilization as well.

I have the other half of the back yard to kill, I'm doing one half at a time so the dog has somewhere to run and play etc. I will do some testing there.

One pound per month? The law here in Maryland is no more than .9 per application, .7 pounds of soluble nitrogen per application, per 1000 sqft. Then there are annual limits depending on types of grass and fertilizer. But it is max 4 pounds per year. How many months are you fertilizing? How do you know there isn't any run off?

Asked before apparently. Somewhat similar responses as here. Link below.

http://forums2.gardenweb.com/discussions/1675689/urea-as-herbicide

@Groundskeeper

I think you're missing the forest because of the trees. The point was that we apply much larger quantities of soluble nitrogen without really worrying about leaching than what I'm proposing as a foliar.

As far as how much nitrogen I'm applying, I plan on applying about 8 pounds per thousand this year, 3 this spring and 5 in the fall. Some controlled release, some water soluble. No limits here in NC as far as I know.

@Pennstater2005

Thanks. I'd like to step outside the realm of theory this time, give it a try and see what happens. I think there's no doubt the grass bladed will get badly burnt - and quickly - I just don't know if the plant will bounce back after a while.

Good point j4c11 regarding large quantities of soluble nitrogen being used. At least it's true for me. I did a fairly aggressive fall urea program for the first time. It's quite a bit of nitrogen plus the winterizer. I'd be interested in your experience using it as a foliar if you do though!

Read THE WORLD ACCORDING TO MONSANTO and you will never use glyphosate again . Unless you want the terminal NonHodgkins Lymohoma then use Urea to kill weeds . I made a saturated solution of Urea and killed Singapore Daisy permanently , while it soon recovers from glyphosate .

What dose of urea you used on 1 liter of water for burning the weed?