I think it's an autumn variant of the yellow one I find from time to time on the bottom of my potted plants (near / on the drain hole). I don't know what it is, either, but at least the yellow one is not harmful AFAIK - maybe this brown one isn't either, except for being unsightly.

Difficult to say what it is. Perhaps a slime mold?

There are people who say "spray fungicide" at any possible sign of fungus and there are people like me who refuse to use it. Nitrogen exacerbates fungal problems, so it's generally good to hold off on fertilizer if you suspect fungus. However you may have had nitrogen deficiency and needed some. Thank goodness you didn't use the urea! Milorganite for the most part is slow release. Try keep the grass blades dry, so if you need to water, do it early in the day so the grass can dry off before evening. If the problem looks like it's spreading and you are worried about major damage, here is some information on the kinds of fungicide least damaging to the mycorrhizae fungi: fungicides and mycorrhizae You had a soil test last year. Did it say you were low in potassium? If you were, Milorganite doesn't provide any. You could use potassium sulfate 0-0-50 to supplement the Milorganite. If the soil test did not indicate a deficiency, don't worry about it. Some general info on mycorrhizae: Mycorrhizae: so what the heck are they?

Oh yeah that looks like spider feet alright. And fungus. Poor fella. There are fungi that attack spiders. I couldn't personally identify any of 'em, but it looks a bit like some of the Gibellula fungi.