Posted: 22/02/2013 at 10:08
Any glyphosate based weedkiller will kill all the existing growth without leaving any harmful residues. Your local garden centre or DIY barn is sure to have a selection.
The weedkiller will need warmer weather and for the plants to be actively growing in order to work so depending on where you live about another 4-6 weeks maybe? It will take about 2 weeks to work and might need another application but a good dig and removal of all remaining roots should take care of anything left.
By then it will be late April/early May which would be a good time to lay the new turf but make sure it is well watered through the summer.