Grub Worms and Army worms are really bad news! Grubs will go after your root systems and can do catastrophic damage. Army Worms will eat the top foliage and are responsible for loss of color in the lawn.
Grub worms feed on the roots of your grass. The damage can be fatal to your turf. Grubs feed on virtually all types of turf grasses. Normally there are not enough of them present in one area of the lawn to show noticeable damage, but heavy damage can occur if 10-15 grubs feed within a small area. Grubs are normally deep in the soil, and come up to feed only certain times of the year.
Army worms feed on the stems and leaves of turf grasses. Damage most commonly occurs on Bermuda or zoysia lawns during the late spring through the late summer. Army worms feed mostly at night. Their damage is best described as wide spread browning of the turf; almost like the lawn is going into dormancy in the middle of the summer. Unlike grub damage, the damage caused by army worms can typically be repaired. If army worms are present you can normally find them if you search in the thatch layer right at the soil level.