I'm no expert, but if you have already mowed twice with the sharp blade, I would think the old damage to the tops of the grass blades should have been removed already, and so I would suspect a fungus. Either that, or maybe your mower is moving too fast to get a clean cut? Though that wouldn't explain the dying grass....

I'm sure pics would help if you can post them.

Curious.

Thanks, I was hoping the F word wouldn't come up, though with all the rain we've had it was on my symptom list. New growth is getting a clean cut. I'd post a picture, but my hobby $ seems to go for other tools - just haven't made it that far down the list to a digital camera yet. I think I'll wait at least another couple of weeks and see if drier weather helps and let the grains get incorporated. Though I'm curious why the Milorganite treated area doesn't show the same problem. An Iron deficiency, maybe?

There is no fungus that shreds the tops of the blades.

True, but a damaged plant may be more susceptible to the fungal infection.

The milorganite areas may be better due to microbe action, or an iron difficency as you mentioned. If milorganite is working for you, than use it again on the whole lawn in late July.

If you have the stomach, try to mow it down to 2.5 to 3" over a couple of cutting and returning to 4" when done. If it is just dead grass that isn't decomposed, cutting it shorter with sharp blades will help it decompose.

If your worried about fungus, a 20 lb/1000 ft^2 application of corn meal with a 3-6 oz milk/1000 ft^2 watering in would help. You can also use cracked corn but corn meal will work quicker as it is finer and has a larger surface area to volume for the microbes to work on.

How are you watering?

So far this season I have yet to water. April and May we got consistent rains above average. More than an 1" per week. This past Saturday was an inch in a couple of hours. I'm watching my rain guage and so far the grass has not cried out for water. I'm mowing at 3.5" and forecast over the next few weeks is to get to 90 so I don't think I'll lower anymore. If I don't see any improvement in the next 10 days I'll try the corn meal and milk treatment. Thanks, I had forgotten about the milk.

None of the symptoms you've describe thus far sound anything like fungus at all. You need some more specific symptoms.