Question: My lawngrass pulls loose from the soil very easily. It's as if something has eaten all its roots. What does that damage?
Answer: White grub worms (larval form of June beetles) devour turf roots (both bermuda and St. Augustine) leaving the grass dead and lifeless on top of the soil. Their prime season of activity starts 6 weeks after the major June beetle flight in early summer and continues until frost. The fully developed grubs are 1/2-inch long. They are white with brown heads, they have legs, and they are always curled into crescents. If you see the damage and find 4 to 5 grubs per square foot, use an appropriate turf insecticide followed by a deep watering to eliminate them. There is little benefit from treating after early November.
On a related note, if you see the same type of damage to St. Augustine, yet you do not find the grubs in the soil, there is the chance that you have take-all patch. It also devastates the grass roots, but you'll just not see the grubs. Use a labeled turf fungicide to stop its spread.