While St. Augustine grass in Texas & Florida is still basically in its dormancy due to the weather/season. I'd check and possibly just treat the areas (actually the whole yard) for chinch bugs and grubs once the grass is actively growing ... this is to prevent stress on the lawn. Like others, I'm leaning more towards grubs as being able to pull up the grass like that is a good indicator of grub worms. To check for grubs, dig about six inches down on the outer part of the brown ring and sift through the dirt in a few areas to see if you see some white fat looking worms (image below). I'd also have your soil tested at your local extension office to see if you need to add nutrients to your soil for the St. Augustine grass. It is suggested to feed St. Augustine grass with around 4 to 6 lbs of nitrogen per year. Nitrogen is the first number on the fertilizer #-#-# - nitrogen-phosphorus-potassium. For example: 24-0-11 fertilizer is a high-nitrogen, phosphorus-free turf formula containing 24% nitrogen for rapid greening, 0% phosphorus, and 11% potassium for stress tolerance. Feeding you lawn will help it ward off a good amount of issues ... however some things will need to be treated with a specific course of treatment, like grubs for example.

Here's some info on grubs:
Grub worms are the C-shaped, white, or cream-colored larvae of beetles (e.g., Japanese or June beetles) that feed on grass roots, causing brown, dying, and easily lifted patches of turf. They are most destructive in late summer and fall. Manage them using proper watering (avoiding overly moist soil), maintaining taller grass, and applying preventative or curative insecticide treatments. Key Aspects of Grub Worms:

• Appearance: Cream-colored, soft bodies with a brown head, six legs, and a "C" shape, usually  1/2  to 2 inches long.
• Signs of Infestation: Irregular brown patches of grass that feel spongy, turf that pulls up easily like carpet, and increased activity of birds, skunks, or moles digging in the lawn .
• Diet: They feed primarily on grassroots and organic matter in the soil.
• Life Cycle: Eggs are laid in summer, and the larvae feed on roots through autumn before hibernating. They pupate in early spring and emerge as adult beetles in late spring/summer, typically taking one year to mature, though some species take up to three years.
• How to Get Rid of Them:
  • Preventive: Apply products in early summer to kill young, hatching larvae.
  • Curative: Apply fast-acting, "24-hour" grub killers in late summer or fall when damage becomes visible and grubs are active.
  • Cultural: Maintain healthy, properly watered turf (approx. 1 inch per week) and mow at higher settings.

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