Answer: Depending upon the type of herbicide you used, the dead grass may or may not need to be dug out and removed. A non-selective herbicide such as Round-Up will kill everything it touches, including the roots. If this is what you used, you will need to rake the dead grass out, including the dead roots. If you used a different kind of weed killer, the grass may look dead on top but the roots might still be alive. If so, simply watering the areas can help regenerate the grass and you won't need to reseed.
If reseeding is necessary, try to wait a month to 6 weeks to reseed. New grass will become established quickly because of cooler temperatures and natural rainfall. If you reseed now, you'll need to keep it watered several times a day until the grass germinates. If you have dandelions in the future, try using a selective weed killer, made especially for broadleaf weeds (such as 2,4-D). Products like these will kill off dandelions without damaging turfgrasses.
Best wishes with your lawn!
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