Yellow spots/rings in St. Aug grass. Need advice (pic link within)

Hey all.
The past month or two, I've been getting increasing (both number and size) yellow rings and circles in my St. Augustine lawn.
See the following page for some digital pictures... The damage actually looks a little less than it was, as I raked out some of the dead grass before these were taken.
http://www.suzyandscott.com/content/grass.asp
After doing some research, I thought it may be brown patch...but they say that usually happens in cooler weather. Houston, TX in August-Sept doesn't really qualify (been averaging 90-97 during the day, 70s at night). The grass is getting enough water I think. One of the bigger spots is in the grade, so if anything it may get too much (although areas around it are some of the greenest in the lawn). The grass definitely gets enough sun. I don't think its chinch bugs, since I've had those before and they were a *lot* more destructive.
This is a new house and this sod was laid in March...everything was fine until this started in July or so.
Is it a fungus? What should I treat it with? If I ignore it and just routinely care for the grass will it eventually go away (maybe during the winter or next season)?
Thanks for any advice!
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It sure appears that the most likely culprit is brown patch (Rhizoctonia solani). Brown patch does not occurs during cool weather, but rather when night air temperatures stay above 68 F and there is continuous leaf wetting for a period of eight or more hours. It is usually worse during rainy and/or warm periods, and on grass grown with high rates of nitrogen fertilization.
In my experience brown patch rarely kills a lawn, but it sure can make it look crappy. Some fungicides, Daconil for one, are effective, but you must make multiple applications once the disease appears.

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