There is only one pre- emergent,(selective) for lawns and that is for crab grass ONLY. Unlike selective herbicides, like broad-leaf weed killers,which can be used year round, there is no selective treatment for crab grass once its up and growing. You will then be forced to either pull them by hand or use a non-selective herbicide,(round-up), and depending on how much crab grass there is, use of the latter will make your lawn look as though you have several female dogs with really powerful urine. Your bermuda lawn should still be dormant,(?) depends on your recent temps, so I would say your not to late, however your window of opportunity is rapidly closing.