I just remembered that the March/April issue of Natural Home & Garden has a whole article on getting rid of weeds in your yard without using chemicals that alter your chromosomes or cause cancerous lesions.

Homemade weed killers:
Boiling water (use a teakettle)
Vinegar

Store-bought killers:
Corn gluten meal
Sprays: St. Gabriel weed and grass killer, Planet Natural's herbicidal soap, and Planet Natural's natural weed killer.

I'm afraid to say anthing more for fear of copy right infringement, if you'd like the details you can check out the magazine article in your library or bookstore. It's called "Whacking Weeds" pg 80-82.
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"If you want yor children to be bright, read them fairytales-- if you want them to be brilliant, read them even more fairytales" Albert Einstein