CONFUSED!!! Some kind of fungus has exploded in my yard...
My lawn was fine one day and then almost overnight it looked like someone had spilled roundup (and they didn't!!) and then walked thru the yard. I dug up a chunk of the sod and took it to Tagawa's and was told the lawn had both brown spot fungus and dollar spot fungus so she sold me a bag of Bayer Fungus Control. Came home and mowed the yard short readying it to apply the fungicide... usually I mow high till the end of the season. I bagged the clippings so as not to spread?... usually I just mulch. Then I raked it well trying to loosen any thatch buildup with a regular metal tine rake, not power rake. Decided to check out this web site (as I do often) before proceeding with the fungicide... sounds like you're recommending NOT using this product. CONFUSED!?!? How do I treat this? I had a friend recommend spraying the yard with a soapy water solution? Appreciate any advice.
Arapahoe County Colorado
Could not zoom your photo much, but it's safe to say that causes other than fungus could result in spotty browning.
If this is caused by dollar spot fungus, you would see "hourglass" shaped lesions on green blades at interface of brown and green grass, as in photos below. It sounds like you've already seen and read http://www.ext.colostate.edu/pubs/garden/02933.html or http://www.ext.colostate.edu/ptlk/1522.html
Dollar spot can be "cured" by mowing higher, applying sufficient nitrogen fertilizer and thorough core aeration....that's why a fungicide is rarely needed.
Soapy water just reduces surface tension of water, allowing it to penetrate further into soils, perhaps even through a thick thatch layer (layer of dead roots at soil surface, as in photo below). Excessive thatch can promote dollar spot, so check to see how thick your thatch layer is - use a trowel or shovel.
Excessive amounts of soap dissolved in water will damage plants.
If browned grass pulls up easily like a piece of carpet and there's a thatch layer, check thatch layer for larvae (photo below) of cranberry girdler (a type of sod webworm). There would need to be 12+ larvae per square foot to do the kind of damage seen in your photo. Plus, you'd likely see some to many starlings and blackbirds on your lawn, trying to feed on these larvae.
Was mower gas tank (over)filled near these spots? Was mower left running for a long time over these spots?
You may bring an 8" diameter and 3" deep sample to CSU Extension office at 5804 S. Datura St Littleton 80120. 303.730.1920 weekdays 8am-430pm. Sample MUST be from transition area green to brown (4" green, 4" brown).
There is a $6 fee for samples submitted. Several photos and diagram should accompany sample.