Where do you live? I live on the edge of the Texas desert in the middle of a drought and have only watered once this year. I would suggest you might be watering waaaay too often and that might contribute to a fungal disease. Is that sand in one picture? Living on sand can be a little challenging. When you do water, how long do you water? Are those spots the same spots where your wife laid piles of leaves or other garden trash for several days before anyone picked them up? Because that is what my yard looks like when my wife does that. If that rings a bell, then it is a fungal disease that will not stop spreading until you do something. Since 2002 (when I went organic) I have had good success stopping it with ordinary corn meal applied at 20 pounds per 1,000 square feet over the entire yard. In fact the entire reason I went organic was due to the success of corn meal in killing this fungus. Nothing I tried had worked before the corn. Anyway, even if you can't remember anything cutting off the air flow to the lawn in those spots, it still looks like a fungus. You applied fertilizer about 6 weeks prematurely. The grass coming back from winter would have looked dark green with or without fertilizer. At this point, in addition to the yellow spots, it looks troubled. It is thin. And are yoou mowing at the mower's highest setting? Without getting the reply to my questions, I'm going to suggest watering less often but more deeply, mowing higher, and fertilize now with an organic fertilizer in addition to the corn meal for the fungus.

Pictures are usually needed but I think you have identified the culprit - fungal disease. I live in San Antonio, TX. I believe we have a similar issue with chemical fungicides. They must be applied when the temperature is not going to be above 80 degrees and no rain or irrigation for 7 days. Well, when is that??? January 3rd??? I had given up on finding a solution when I heard a guy on the radio suggest using ordinary corn meal on plants with fungal disease. I tried it on a rose plant and it was cured in a week. Nobody was more surprised than I was. Next week I listened to that radio guy for 3 hours. That day I went out and bought 50 pounds of corn meal at my local feed store. The rest is history. Since then I have never been afraid of a fungal disease. I have watched my garden carefully and have even identified the cause of my fungal disease issues. It is my wife leaving garden clippings on the lawn for a few days. Dew forms and the normal air flow is choked off by the pile of clippings. She had one favorite place to put the clippings so I just pretreated it with corn meal every spring. Now I have her putting them in the compost pile or on the concrete until they can be disposed of. The application rate to get rid of disease is 20 pounds per 1,000 square feet. You should apply to the entire lawn so you don't end up with green spots where you applied it. Corn meal is an organic fertilizer, too. Having said that and rereading your original message, if you have already used a fungicide, then corn meal may not work. Corn meal relies on the fungal health of the soil. If you have sprayed a fungicide then you have no fungal health left. You might want to apply compost first. Give the compost 2 weeks to work and then use corn meal. Then give the corn meal 3 full weeks to work. I would reapply after 3 weeks whether you have seen progress or not. The second app at the third week will thrive on the back of the first dose and should supercharge the antifungal effect. Most people wonder how corn meal works to kill fungus. The original TAMU work showed that corn meal contributes to the growth of the Trichoderma fungus. Trichoderma is a naturally occurring, predatory fungus that feeds on the cellular structure of other fungi. Normal soil has Trichoderma but not in high populations. Corn meal is decomposed by another fungus that multiplies the population of Trichoderma.

It's not SAD, it's normal. It has happened to me for 15 of the last 20 years with no apparent permanent issues. Besides 1 inch of mulch over top of St Aug is GUARANTEED to suffocate it and eliminate the lawn completely. But I'm not surprised TAMU would come up with that bonehead diagnosis and worse solution. That is a great picture. I've been trying to find a good lawn to use for an example of this problem. The problem is the heavy rains we had washed all the acidity out of the soil. When that happens, the pH at the very surface goes to 8.0 and the iron becomes bound up and unavailable to the plants. If you do nothing, it will remain that color for the rest of the season, and next spring, all will be great again. You may not remember that you had a problem. What seems to happen over the winter is the soil pH in the upper root zone becomes more acidic...just enough to release the iron for uptake in the plants. At this point, no matter how much iron product you apply, the high pH will never allow it to reach the plants. One product that seems to work, and the reason is not crystal clear, is called greensand. The actual material is glauconite (GLAW co nite). It is mined from ancient seabeds in various places around the country. It is sandy and has a greenish tint. Apply at 40 pounds per 1,000 square feet and you have a chance of full recover this season. If you live north of Austin, I would not bother for this year. If you live south of a line from Corpus to Laredo, then you might want to go ahead and do it, because you have many weeks of active growing grass left this season. I live in San Antonio and have a house in George West - I'm not going to use it on my lawns. At least you can live in comfort of knowing the problem happens all the time. It has no effect on the health of the grass or soil. The reason it happened to you and not your neighbors might have to do with the fertilizer they use. If they use one with ammonium sulfate, it could be their pH is lower. I use only organic fertilizers with no "acidifiers," so if it is going to happen, it seems to happen to me. Greensand clears it up after about 3 weeks. You should be able to get greensand at any good nursery or garden center. This only happens in years with heavy rains. One year we had a low pressure system stagnate over top of us dumping 20 inches of rain in a week. At about day 4 of that event, I realized what was going to happen and applied the greensand while it was raining. It worked perfect! I had the only deep green lawn for the rest of the year while everyone around me went entirely yellow.

I'm guessing that you are watering too frequently, possibly daily, which has led to the lawn developing a fungal disease. Notice that there is a distinct arc to the brown blades from the bottom right of the picture to the middle left...that is another clue that it's a fungal disease and not caterpillars (worms). Quite often a fungal disease will form a near perfect circle. Can you post another picture? Get about 3 inches away from some of the grass at the edge of the brown area. The best pictures are taken on a cloudy day or in the shade to reduce the contrast. Fungal diseases show up on the blades of grass. If it is a fungal disease, my recommendation would be to apply ordinary corn meal at a rate of 20 pounds per 1,000 square feet. Corn meal attracts a predatory fungus which feeds on the disease fungus. It goes to work immediately but it takes about 3 weeks to see the improvement as the green grass returns. I have used corn meal successfully every year since 2002 to eradicate disease in my St Aug. Although, now that I have Floratam in the back yard, the grass fights off the disease faster than it can spread. I still see signs of disease...and then it's gone. If you don't have Floratam now, you might consider putting down one flat of it and letting it spread into the lawn. If you had Floratam in the lawn currently, it would be spreading into the thin (brown) areas and taking over even while the disease is present. Cool stuff. Oh and as to the watering, this time of year you should be watering no more frequently than once every 2 weeks in your area. If you get high temps in the 70s, then you could back off to once every 3 weeks. If you are not doing that, please write back and tell us what you are doing so we can get you backed off to watering less often.