Where do you live and what kind of grass do you have?

What is your watering schedule? How often and for how long do you water?

Over watering is a prime reason for dying grass, but usually it looks different from what I see in your pic. Grubs are usually only a problem in late summer. Use a grub treatment in the spring is wasteful and unnecessarily toxic to other beneficial insects. I'm thinking the problem was caused by too much water, possibly standing water, in those spots. Need more info from the questions above to get a better diagnosis. Also could you get down into the grass and take a picture from 6 inches away. Take the pic at the fringe where the grass is green and where it is brown.