Zoysia, St. Augustine and Bermuda grass are all common lawn grass choices due to their heat and drought tolerance. While some varieties tolerate the rampant heat, humidity, weather extremes and often unfriendly soils native to south Texas, all can be damaged by insect, disease or environmental hardships. The indicator of this damage most often shows up in the form of brown patches or spots in the lawn
Chinch bug, grub worm and cutworm infestations will cause patches of lawn to turn brown as the bugs eat the lawn. Large swaths of brown that show up during warm weather in moist soils are likely fungal diseases, especially if the grass is watered in the evening. Excessive hot, dry periods common to south Texas will cause even drought-tolerant Zoysia lawns to turn brown in places. And despite the infrequency and relative mild nature of cold snaps in south Texas, they can make patches of St. Augustine will turn brown and Bermuda grass go dormant.
If an entire area has turned brown, it's likely that the grass is dead down to the roots. The exception to this is Bermuda grass lawns that go dormant. Lawn grass will re-grow over dead spots once the cause of the problem has been dealt with. For especially large patches of brown grass, the recovery happens slowly from the edges, leaving the center of the brown patch open to weed infestation, drying out and possibly erosion if the roots are gone.
Fungal diseases in lawns almost always stem back to improper watering practices. During warm weather (which is much of the year in south Texas), water only in the early morning, and no more than once per week. Yes, even during the summer. Water at least 1 inch, and remember that if your yard slopes you will have to water slowly to prevent the moisture from running off before it soaks in. Install drought-tolerant lawn cultivars to fend off devastation from drying out and chinch bug infestation.
Check with the Texas extension services for availability of beneficial nematodes to fend off grubs. This is a slow solution, and you have to avoid using insecticides on your lawn. But nematodes often stick around for many years, so you don't have to re-apply noxious and expensive pesticides every year. Chinch bugs can be treated with insecticides, but that also kills the predator bugs that could be eating the chinch bugs for you. Water deeply and regularly during droughts in the hot summer months until cool weather immobilizes chinch bugs. Add a 1/4-inch layer of compost to the lawn to help combat fungal diseases.
Frequent use of high-nitrogen fertilizers, close mowing and frequent watering are all culprits of brown spot problems in lawns. Nitrogen fertilizers will even exacerbate fungus problems. Allow your grass to grow a short while between mowing, mow only down to three or four inches, and avoid shallow, frequent watering. Use compost on your lawn and mulch with the clippings instead of fertilizing. Healthy lawns resist environmental damage better than weak lawns.