Many weeds are more easily prevented than cured once we have them. A pre-emergence herbicide is applied to the ground before weeds come up. It prevents them from getting started. Many winter annual weeds have been prevented by applying these weed preventers in late September or early October. Most of the type chemicals must be used before weeds come up.
Timing is critical.
There are several types of preemergence herbicides. Do not use Atrazine on green Bermuda grass lawns, it may burn them. It is okay to use on dormant Bermuda. Some weed and feed fertilizers have these pre-emergence chemicals in them. The problem with them is the fertilizer should be applied in April while the weed killer should go out now.