re: Lawn issue: dead grass base

Is probably thatch, and may be caused by frequent but light watering and over fertilization causing the roots to grow lateral instead of deep, then become damaged by sun and heat

Rent a dethatcher from Home Depot and run it , will Make your lawn look like shite for a few weeks, but then become very healthy

Also stay away from the "Scott's" system and next year only apply a pre emergent weed killer early spring then a variety specific fertilizer after green up is complete

Cut your grass at a high setting on your mower

Take a soil sample and send to LSU