Willy for some reason your other post has the comments turned off. You might want to repost. I have let St Augustine grow up to 32 inches high, which seems to be the limit of growth. Then I "mowed" it back down with a string trimmer and kept it at 12 inches tall with a string trimmer. So there is nothing going to happen if the grass gets too tall. The taller it is the deeper the roots go. The deeper the roots go the less irrigation you need to apply. My tall grass St Aug went for 36 months with no irrigation, and it looked fine(ish) through all the droughts we had. As soon as the rains came again the grass, of course, perked up. The point is the taller it is the better it will make it through the summer. I just trimmed my current lawn down to get the few pieces of weed stems out, but I tried not to cut the actual grass. This is on a south facing slope in the heat of Texas, so I'm trying to keep it alive with once a week watering allowed around here. It looks very good considering the situation. I attribute that to the length. So you can mow if you want to. If you decide not to mow right now, then when you finally do mow, bring it down by about 1/3 with a string trimmer for your first cut. Give it a couple days to rest and regrow, then bring it down to the final height or by another 1/3 if the grass got pretty tall. Then mow at the mower's highest setting all the time. There is never any reason to mow St Aug at any other setting.

You should be watering 1 time a day every day for the first week.Every other day the second week.Every third day the third week.Twice a week from there.To much water to often leads to shallow roots and poor drought tolerance.Less freqent but deeper watering is perferred.Also use a slow release fert like scoot cat recomends4 times a year.Or use a time realesed fert as recomended on the bag.Never use a fast release fert because of run off and the fact that N is highly mobile and moves through the soil very fast.This causes a nutrient spike after the app followed by a steady decline in avalibilty.

You could do 50/50 of soybean meal and alfalfa pellets (not meal) at the rate of 30lbs per 1000 sqft to feed the microherd in the soil. You will have to spread each separately with rotary spreader. Use the highest setting for alfalfa pellets and probably halfway between highest and lowest for soybean meal. Do you have ortho-dial? You could get unsulfured blackstrap molasses and APPLE VINEGAR (not the fake one). again 50/50 at the rate of 4oz per 1000 sqft after you've spread soybean meal and alfalfa pellets. Mow at the highest setting. Water deeply whenever large area are wilting. Try to go as long as you can between watering.

Looks like it to me. Here is a link to some more information, which you might have already found. I would assume the grass came with the disease which got much worse with the rain. Take a note and don't buy grass from that supplier again. Being an organic kind of guy, I would be hitting the grass with ordinary corn meal at 15 pounds per 1,000 square feet every 3-4 weeks for the rest of the summer. This is INSTEAD of using a fungicide. As discussed in the link above, this is a soil borne disease. These problems are caused by an imbalance of beneficial versus pathogenic microbes - essentially an unhealthy soil. The fastest way to restore the soil to health is to use organic fertilizer, NOT fungicide. Corn meal has the additional benefit of heavily populating the soil with a predatory, but beneficial fungus called Trichoderma (try koh DER mah). Not all fungi cause disease. If you cannot find ordinary corn meal at your local feed stores (call first), then cracked corn will work. If you cannot find either one, then look for a grocery store catering to the Hispanic market. They will have 25-pound bags of corn flour. They will also have 25-pound bags of tortilla ready-mix which has baking soda and baking powder in it. The bags are almost identical, but you want the plain corn flour. Ask for help if you cannot tell them apart. If you have any doubts about the effectiveness of organic fertilizer, please ask. I think you ran into an unfortunate weather situation - unlucky timing. The grass could have been afflicted before you bought it, but that's hard to prove. It may have a guarantee or you might get a discount on buying again from the same supplier.