Thanks for the question.

Four immediate possibilities come to my mind:

1). There is a dearth of water in these areas. I rather doubt this is the cause given the ample amounts of rain recently received in the Metro, but out of necessity felt I should mention this. In any event, be sure that these areas are well watered.

2). There is some type of fungal infection. They often pop up at this type of the year. However when they occur they often present themselves as irregular patches, not following straight line areas.

3). Your second picture is very informative. Note the straight lines of the dead area. As mentioned, this is NOT consistent with a fungal infection. I realize that you first stated that no chemicals were used on your yard. But yet this picture suggests that a cart containing some type of chemical might have been inadvertently pushed over the garden’s limits. Perhaps this involved the application of fertilizer onto a garden? Have you recently had a lawn service visit you?

4). There might be grub activity. But yet, again this is not consistent with the well defined area of dead grass. Nevertheless, pull up some of the dead areas and look for the presence of white grubs with orange heads that curl up when you expose them.

As for remedial procedures, here are my suggestions:

1). For the immediate moment, I do not think that you have a serious problem. With time, I believe that grass will return. Continue watering, especially focusing upon these dead areas.

2). It will be important for you to ascertain whether or not any herbicides are culprits. Ask your your neighbors about any of their activities. You said this came on rapidly. This not consistent with a fungal infection. Have you recently had a lawn service do anything? What about your putting down any type of garden fertilizers?

Bottom Line: in my opinion, your grass is not completely dead. It is just suffering from discomfort at the moment. It can quickly be improved. If you wish, do a vigorous raking and remove the dead grass. Sometimes the surrounding grass can fill in the brown areas. Doing grass seeding at this time of the year may not be very productive. But if you do so, don’t expect quick miracles. Please keep us informed. Trying to grow grass at this time of the year f(approaching mid-June 2022) can be a challenge.

Finally, I really have no idea what you mean when you say you "mowed 1/3 and 1/3".

Good Luck!!