A few industrial sized bags of salt should do it...
Your yard is just dirt right now? Try Total Wipe Out Concentrate. It's perferct for newly built homes with dirt yards cuz it kills everything, weeds, grass, flowers... And since you only have weeds, yer good to go.
Just checked online, you can get it at Canadian Tire and they're giving 5x BONUS CANADIAN TIRE MONEY for buying it. OMG!!
