Hi Brian,

Thank you for contacting us at the UNH Extension Yard & Garden Infoline.

I am so sorry to see that your grass is not doing well this month! It is tricky to say 100% without submitting a sample for testing to confirm if this is strictly due to grub damage or a midsummer fungal related disease. I would strongly recommend submitting a sample to our plant diagnostic lab for further diagnosis/confirmation: https://extension.unh.edu/agriculture-gardens/pest-disease-growing-tools/plant-diagnostic-lab. I will also share a selection of educational resources below that speak to both possibilities and I hope these references help to gain more insights!

Grub related resources and how to prevent damages:
https://extension.unh.edu/blog/2019/09/how-do-i-treat-grubs-my-lawn
https://extension.unh.edu/resource/grub-control-video
https://extension.unh.edu/sites/default/files/migrated_unmanaged_files/Resource002814_Rep4169.pdf
https://extension.sdstate.edu/white-grub-damage-lawns

You can attempt to survey areas in your lawn for signs of grubs:
" Heavy white grub infestations can destroy grass roots, causing the affected area to become spongy, which allows the sod to be rolled back like a piece of carpet. Evidence of grub damage, including patches of dead or dying turf, are visible during spring (April and May) and late summer and fall (September and October). A good indication of a grub infestation is the presence of skunks, crows, or moles feeding on turf. However, remember that moles also feed on earthworms or insects living on shallow tree roots. The symptoms of a grub infestation are not always obvious. Survey and map the area in question to be sure an infestation is present. Using a garden spade, remove one square foot of turf and soil (two to four inches deep) at several locations. Examine the soil, thatch (excess grass cuttings and debris), and turf thoroughly for grubs. When the examination is complete, lay the sod back in place and pack it in firmly. Watering in the areas previously sampled is advantageous to prevent the area from drying out and dying." https://extension.psu.edu/white-grubs-in-home-lawns

Possible fungal related issue - patch diseases and more - many of these diseases thrive in high temperatures and high humidity conditions:
https://extension.unh.edu/sites/default/files/migrated_unmanaged_files/Resource000567_Rep589.pdf
https://extension.unh.edu/resource/rhizoctonia-brown-patch-fact-sheet#:~:text=Rhizoctonia%20brown%20patch%20is%20a,feet%20or%20more%20in%20diameter
https://extension.psu.edu/turfgrass-diseases-brown-patch-causal-fungus-rhizoctonia-solani
https://extension.umd.edu/resource/brown-patch-lawns/
https://apps.extension.umn.edu/garden/diagnose/plant/turf/circular.html

Best of luck with your investigative work here! Please reach out if you have any further questions.