Do you have pets? They look like dog pee spots. One thing I have found that works on dog pee spots is table sugar. Yes, I know it sounds stupid, but it worked. Scatter a heaping handful of sugar on each spot and moisten it - don't wash it away, just moisten it. Check again in 3 weeks to see if it looks better. The background is that the dog pee has too much ready nitrogen for the soil microbes to handle all at once. By adding sugar, the microbes begin to repopulate and soon enough have sufficient population to deal with all the nitrogen. Within 3 weeks you should see very tall, and very deep green, grass on those spots. It's just like you fertilized - which is sort of what you did.

Thanks dchall. I don't have any pets. No animal has entered my property since I installed a fence 2 years ago. I'll try the sugar trick though :)

Sorry, double post.

This post was edited by tonyastro on Fri, Feb 21, 14 at 15:39

Well, for anyone else with pets, that's how you fix it!

Okay I should have asked this first. Especially since I just noticed zone 9.

Where do you live?
How often do you water and for how long?
When were the last two times you fertilized and what did you use?

My reply didn't go though for some reason so here it is again:

I think I got it. I noticed some white cottony stuff on the soil and when I looked it up it looked just like fungus which has been known to cause brown patches.
http://www.ipm.iastate.edu/ipm/hortnews/files/images/pink%20snow%20mold%20on%20turfgrass%20fig%204.preview.jpg
Hopefully a fungicide will do the trick.

This post was edited by tonyastro on Wed, Feb 26, 14 at 17:56