We have always had a beautiful, plush lawn, and this year it looks TERRIBLE!! Our new lawn service fertilized about 2-3 weeks ago, but since then with the HOT weather - we have these dried up -dead looking- bare spots mostly where the hot sun hits- not in the shady areas. Our lawn service said it is a fungus and our neighbor’s lawn service said it was insects.
Summer fertilization can damage heat and drought stressed lawns. Use a slow release preferably organic nitrogen fertilizer, like Milorganite, to avoid damage when fertilizing in the summer. Fertilizer and herbicide damage can cause the damage you describe as can the hot dry weather, insects and diseases. Hot dry weather usually means fewer diseases and more insect problems. Check for insects before spraying. Applying an insecticide to the lawn can kill many of the beneficial insects that keep our lawns and landscapes healthy. Dig around in the grass or sprinkle soapy water on the soil to irritate the insects and bring them to the surface and find out if you have a problem. Make sure the insects you discover are harmful before treating. In the meantime water thoroughly whenever the top few inches of soil are crumbly and moist or your footprints remain in the grass. Water early in the day to limit water lost to evaporation and to avoid disease problems.