Too late for winter weeds
You may be seeing alot of weeds in your yard at this time of year, but a post emergent herbicide will not manage these mature weeds. Even though post emergent herbicides are labeled to manage weeds that have already emerged, they only work well against small, young weeds. Once weeds grow well above the turf, begin to flower or seed, herbicides will not be very effective. You may burn a little of the plant, but you will not kill the weed.
At this time of year, you may still apply a pre emergent herbicide to lawns to managing germinating weeds. Be sure not to overwater after applying a pre-emergent or you will wash the herbicide out the soil zone where weed seeds are beginning to grow. Always make sure your specific herbicide is labeled for your lawn and situation. Read the label to be sure and to protect yourself and the environment.
If you have a lawn professional treat your lawn with chemicals, always make sure they hold the appropriate pesticide license.