There are ways to attach more than one photo. Gardenweb has a help area just for that. Search for "posting photos" and you should find it.

This is definitely a fungus problem. When the spot is a perfect circle like that, fungus is the easy answer. You are probably watering too much and too often. The only time your lawn should need to be watered weekly is in the hottest heat of summer. In the winter it is more like monthly. The surface of the soil should be allowed to completely dry out before watering again. You'll have to watch the grass for signs of wilting. If it wilts, water it NOW but water it for a longer time than you watered before. Water deeply, not for just a few minutes. Generally we talk about watering a full inch, all at once. Spreading out your 1 inch into seven days is definitely NOT the way to go. And withholding water like I'm suggesting is the best way to keep weeds away. Weed seeds like continual moisture to sprout. If you let the surface dry out, they won't. Of course the rain may sprout them but you can't control that.

Assuming this is St Augustine grass you should mow at the mower's highest setting. As an experiment I have let my St Aug go unmowed since October of 2011. Some places it is 36 inches tall and in others it is under 6 inches. The taller grass is under the shade of live oak trees. One place has not been watered one time (except for rain) since 2011. This experiment is to see what effect tall grass has on watering. Clearly tall grass needs less water than short grass. Most people have an HOA or neighbors who will jump all over you for letting your lawn get out of control, but I live on an acre in the country and can get away with it.

I have had good success with ordinary corn meal to treat fungus like that. Since 2001 it has worked every time I tried it. Apply at 20 pounds per 1,000 square feet over the entire lawn and reapply in 3 weeks. If you only applied it on the disease spots you would end up with dark green spots instead of brown. That's because corn meal is an organic fertilizer. Do the entire yard.

dchall, thank-you for the response...

I'm in the process of looking for a fertilizer spreader, found some on craigslist, but someone beat me to it; oh well, better luck next time. Question about corn meal, it is in powder or pellet form? The only feed store that I know of around this area is Tractor Supply.

Back to the topic, I've turned off the irrigation system for the time being and will keep an eye on it.

Here are some of the weeds I have on the lawn...

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These seems like a lot but its not; they're small in area but spreads around the yard. what is the best way to deal with these weeds?

Thank-you.

You can pull those weeds or you can spray them with a product that does not kill the lawn. St Augustine is sensitive to herbicides. One herbicide that works is Atrazine. Here is a picture of one product...

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Thanks for the photo, this helps a lot.