Answer: I'm not sure what is going on with your lawn. Crabgrass preventer must be applied before the crabgrass seeds have germinated. March is the best month to apply in your gardening region. If applied too late, the seeds will already have germinated and the preventer won't kill the weeds, but future seeds won't sprout so you will have less crabgrass than if you did not apply it at all. As for the deteriorating lawn, you may have applied too much of the product, or forgot to water it in after application. At this point I can only suggest you water regularly to help dilute any excess salts and to encourage healthy new growth of your lawn. Later this season you can rake out the dead grass and overseed. Fall is the best time to reseed lawns in your growing region.
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