It would be wise to start the grubicide program this fall. I put in a new lawn . Nothing but weeds came up. If you do not have 8 inches of loam, forget about growing a lawn and put in a rock garden with pockets of soil for the plants. If a grass root is stifled, the crown will suffer disease.
Crabgrass spreads like grazy in hot dry weather.
Rather than trying to kill the weeds, I would turn the entire would be lawn over. Cut the entire area as low as possible and rake out the clippings. Rent a heavy duty tiller and turn it in. Plant a new lawn with the neccessary depth of soil. The best weed control is a good tight lawn.