Good picture. See those two blades of grass that run left to right and almost parallel in the picture? Those both look like they are covered in white spots. Can you verify that in person? If that is not an illusion, then you do have a fungal process going on. If you can find those grass blades, watch them to see if they die in the next day or two.

My first line of defense for fungal issues is corn meal. Ordinary corn meal attracts a beneficial and predatory fungus which feeds on other fungi. It will take out most lawn diseases. Since this is a biological process it takes about 3 weeks before you see the grass coming back in.

Summer heat is a bad time to apply chemical fungicides. Maybe someone knows of one that will work. If you apply a chemical first, then the corn meal will not work, so that's something to keep in mind. You can use corn meal first but not second.

The best place to get corn meal is at a feed store or farm and ranch store. Call first to see if they have it. You want ordinary corn meal, not corn gluten meal.

I'll try to check that spot again, but my inclination was also that it was some type of fungus. I actually treated my previous lawn with cornmeal after a fungus problem from reading some of your posts on here and it worked great. So thank you very much for commenting! The only thing I don't remember - is it necessary to water after applying the cornmeal?

Nature will water it in for you, but if you want to get the process going, damp it down in the morning after you do it.

Evenings aren't wise as that's going to encourage the fungus you already have, and there's no sense in setting that off.

I agree, nice picture. I'd agree that given the age of the turf, the season, the amount of moisture, and the application of N......disease is likely. Google 'Pythium'. It's a fast moving disease that can be quickly be devastating to new lawns. Bring yourself up to speed on the symptoms and the conditions that favor it. Then do your best to minimize those conditions that favor the disease. All species of turf are susceptible to Pythium and its soil borne and a potential problem in virtually all soils. If you start to notice die-back in patches, often in low spots, etc. Fungicide is your ONLY help and only a handful afford protection. Google both Subdue and Disarm. Both are available as granular and provide 3-4 wks protection. Might be only professional usage, so check locally and see what's out there. I'd also encourage a soil analysis ( if you haven't done one ). Sandy soils are almost always N and K deficient and an analysis will be helpful for determining a baseline for macro and micro-nutrients. Consider the report a starting point. I'd suggest you also request recommendations. Again, a starting point. Another fert comment. Sandy soils are typically quick to leach N, especially with the more frequent irrigations during establishment. Therefore, I'd suggest using blended N's. Those would be products featuring both slow and fast release N. Polymer coated ureas (PCU's) are awesome for sandy soils. Sandy soils are also a great place for bridge products containing both organic and synthetic forms of N. Bottom line, see what's available at your professional outlets, get on a program, and stick with it.
Good luck! PG78