Lawn diagnosis required

Our lawn has several large dead spots. One is about 4' across on the sunny part of the lawn, another is about 2' across on the shady part of the lawn and a third consists of a bunch or small circles that have not YET joined together to form one big dead spot. These spots started appearing about two months ago or perhaps more correctly never recovered from the dry spring like the rest of the lawn. I fertilized in late May and did not start any watering until mid June.
The nominees for the dead spots are:
1) Dry spring. I started watering too late and some patches never recovered. But I never watered the back lawn (shady) and it has recovered nicely after the recent rains.
2) Fertilizer burn. Perhaps, but the telltale bright outer ring is missing and no amount of watering has helped this. Also, the same dufus (moi) fertilized the back and front lawns.
3) Crappy sprinkler coverage. We had one impact sprinkler that I moved around and there is no question that it misses spots. But this has not been an issue in other years.
4) Mould or Fungus. I have no experience with this.
5) Grubs. This seems to be the opinions of neighbours and others, but the Skunks and Raccoons do not concur. Also, I have excavated two 1' square patches, one in the dead zone (3 weeks ago) and one outside the dead zone a few days ago. I found ZERO grubs. Perhaps I waited too late to dig up a test patch, but we have had no Skunks or Raccoons digging up the lawn like other years. We have also had the lawn treated with Merit several years in a row, although not last year.
Your advice would be appreciated. I'm leaning toward a combination of 1 & 2, but I have no experience with Mould.
We recently had REAL sprinklers installed, as we plan to put some soil in the dead spots and seed them. But I'd like to solve any underlying problems before I do this.
I'm in Zone 6A (Southern Ontario)
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Bill Stock wrote:

I have the same problem. I don't water at all because the Town doesn't permit it. I put down fertilizer twice and real lime once. From my reading there is a common bug that eats the grass roots and spread out radially. You can peel up the dead turf like a carpet. I dusted with a bit of Sevin, but I believe any insecticide would do.
There is a chance this is a fungus (Fairy Rings). I'll spray with some fungicide if it doesn't start recovering soon. In then end, scrape it up, add some seed an starter fertilizer and wait for Fall rain.
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Time to turn a usless lawn into a garden..How much more fun to tend a garden where the colors change and brighten the day than green grass that requires nothing so much as mowing, pesticides, valuable additional water, for what?
alice
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