Most lawns we service in the area have St. Augustine turf so this information will be specific to St. Augustine. However, most of these points can be applied to Bermuda and Zoysia as well.
1. Any sign of discoloration in the lawn is generally assumed to be a lack of water or heat stress my most homeowners. While common this time of year, it is not always the case that you just need to water more to correct your problem. In fact, over watering can be one of the leading causes in fungal growth in the lawn that usually produces patches of brown colored grass in the lawn.
2. Heat Stress in St. Augustine does not immediately turn the lawn brown and takes several days and weeks without proper moisture to completely go dormant or brown. Its first reaction will be for the blades of grass to begin to contract as a form of protection. This leads to a visible contrast in your lawn that might be seen initially in patches of your lawn.
3. Disease or fungus comes in the form of brown patches in your lawn, but there is typically some signs of green mixed in early on before the disease continues to spread. These spots will become more brown the longer they go without treatment, however, the easiest way to tell the difference between disease and pest issues is by completing a simple pull test. More on that below.
4. Lastly, large brown spots in your lawn can form because of pests damaging the grass and often times they are below the surface eating at the roots which leads homeowners to believe the grass is dying because of a lack of water. To test for bug damage, simply give a light pull on the damaged grass blades. If they easily pull out of the ground without much effort, you very likely have pests that are eating at the roots and need the appropriate treatment to correct.
In all cases, these issues can be prevented and treated with proper agronomy practices in your lawn throughout the year by applying the right amount of water, controlling thatch with annual aerations, and keeping your soil pH balanced.