In article , PA
writes
thanks every one for your input, I'm still in two minds though....
the bit I don't get is: if no residue is left in the soil, what about when
the roots of the weeds start to break down wont they release chemicals,
which will be then taken up by whats ever growing?
Most of the roots will not break down, they will survive and re-grow
with increased vigour to replace the temporarily wilted plant tops.

If glyphosate is used as a spray, it can carry by air for quite a
distance depending on atmospheric conditions at the time of use. Small
quantities of it settling on nearby food plants will render them unfit
to be described as organic grown. Commercial growers attempting to sell
affected crops have lost their organic certification by that means.
--
Alan & Joan Gould - North Lincs.