Grubs or Grubworms can be an issue in turf from June to October in our area. The easiest way to make sure your lawn has a grubworm issue is to dig up a foot square section only a few inches deep. Look for the white larvae. A lawn with a grubworm infestation. The sample should contain numerous grubs. The absence of the larvae will indicate another turf problem. A lawn with grubs will have weak appearing grass and can be easily pulled up by the handsfull. As the grass will have little or no roots.
Attached is a comprehensive information PDF on Grubworms. Please review for a complete explanation of grubs life cycle and treatment options.