Corn meal at 20 pounds per 1,000 square feet should do it for you. Have you checked for grubs in your problem spot? Dig up 1 square foot of sod and count the grubs you see. If you have 12 or more, then your problem is grubs and the organic solution is beneficial nematodes. If you don't see enough grubs to be a problem, it could possibly be another bug and, again, beneficial nematodes is the solution.
Time is of the essence to get this fixed before the end of the season. I would order the beneficial nematodes immediately and then go digging around. The brand of BN I like is the
Guardian Lawn Patrol out of Colorado. They come as a smear on a damp sponge. You wring the sponge out into 5 gallons of water and then spray the water onto the soil. They have to be kept moist so they work best in pretty damp soil (think a week of rain).