thanks for all the info, dandelion is edible by the way [if you don't spray it with roundup] and if you would like to eradicate it, you must pull ALL of its root system or it will return...
the use of DDT was much the same, except used decades earlier; it took 20-30 years and a biologist to lead the way to a worldwide ban -- it is still found in the earth today....
http://en.wikipedia.org/wiki/DDT