I suspect a) chemical injury but it might also be b) Spring/Fall leaf blight too.

a) You have done the right action by watering to dilute the chemical concentration.  Correct the problem so you don't repeat it again next time.  Consider spot spraying only the weedy areas of your lawn if "much of the lawn did not even have weeds".

b) Spring/Fall Leaf Blight is a fungal disease where the leave die back from the tips.  Most prevalent in warm (60-80F) - humid conditions.  More severe on stressed turf or turf treated with grass herbicide.  Cultural controls include:  1) maintain adequate fertility, 2) mow at species recommended height, when turf is dry, 3) minimize leaf wetness and 4) avoid herbicide applications when periods of hot, humid weather are expected.

Tips on lawn maintenance:

Get a soil test to know the soil your turf is growing in. Knowing the condition of your soil is the starting point to establishing & maintaining a good lawn. More info here: Don't Guess-Soil Test-MSU and MSU Home Soil Test-self mailer

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