I used to spend a lot of time in Middle Tennessee visiting around Tullahoma. Wish I had paid attention to the lawns when I was there. I think I remember a lot of common bermuda out in the sunlight. Back in the trees I'm not sure what I saw. I am sure it wasn't zoysia, though. Who is recommending Emerald? Is it someone selling it or someone who has had it in their lawn for 20 years? In my limited experience with zoysia...if you fail to water it before you think you need to water it, it will go dormant on you. Once it goes dormant from drought, no matter how much you water it, it can be weeks (and WEEKS) before you see any sign of green. Mine is not the Emerald variety. If you are willing to water once a week, then St Augustine should work. If you are unwilling to water, then buffalo grass will work but only in full sun. Bermuda will survive the conditions you say but if you want it to look nice you would have to water it every week or so, fertilize it heavily every month, and mow twice weekly. You don't sound that ambitious. The seeded varieties of buffalo will not grow in dense. They quickly become weedy and look like pasture. One variety called Tech Turf grows very dense. St Aug and Tech Turf both thrive when mowed at your mower's highest setting. Both would spread once established and fill in without having to cover the entire half acre. Unlike the fescue, though, all the southern grasses will go dormant (brown) in the winter. Suck it up and get used to that feature. Another alternative would be native prairie grasses. Some of those, when mowed like a lawn, look excellent. They never need water (in Tennessee) and never need fertilizer. They do require full sun, like buffalo grass and bermuda do. Zoysia is known for being v-e-r-y slow to spread and slow to recover from damage. Anyone who tells you otherwise is probably trying to sell it to you.

How often are you watering? How much rain are you getting? I don't know St Aug grass very well, but if you're still watering the way you were when the sod was first put in, you're probably watering too much, which could be giving you fungal problems or saturating the soil and killing the grass roots.

I have been watering at night three times a week. There is your problem, you are over-watering at the wrong time and now have a fungus called BROWN PATCH. Also sounds like you are not mowing enough. Zoysia is very drought resistant, and should only be wayered when it is needed in the morning hours, not at night. You need to learn how to water properly and when to do it. Basic rule of thumb is once a week at a rate of 1-inch per application. If Mother Nature provides water, you don't. The best method is to lok at the grass, it will tell you when it needs water. Emerald Zoysia needs to be maintained at 1-inch, therefore mowed every 4 to 7 days.

You will not be over-watering. You will want to keep watering on that schedule for as long as the heat wave lasts. You will want to water 4 times per day for the first 12-14 days. Then when you can't pull the sod up because the roots are taking hold, that is when you start to back off the watering frequency to allow for deeper root growth. Remember, do not over-fertilize zoysia. Zoysia only needs about 2-3 lbs. N/1000 sq.ft. per year. Mow at 2" height of cut. For the rest of this first season, I would advise you to collect your clippings. Also, be observant of turf disease during this time of heavy watering in hot, humid weather. I hope you enjoy the beauty of your new zoysia lawn.