I must admit I'm pretty reticent to use chemicials in the garden - especially after discovering the reasons why Derris Powder (used to get rid of ants and other such creatures) is likely to be removed from shop shelves in the UK by September 2008 (according to Garden's Monthly Feburary 2008). Rotenone is a natural product extracted from the roots of derris plants and has been found to possibly contribute to the onset of Parkinson's during recent research in the USA at Emory University in Atlanta. I've never liked the idea of using chemical weedkillers particularly on an area where you are going to grow vegetables despite the instructions on glyphosate saying that it is quite safe for this purpose and would rather resort to more organic methods.
Happy digging!!