Grub Symptoms and Damage
White Grub damage mimics water stress and water stress mimics grub damage – the two are hard to tell apart. The best test is to half kick, half scuff your shoe like you’re trying to move a throw rug - if it doesn’t move – fix the irrigation. If it does move like a throw rug on a terrazzo floor – you have grubs. If you look under the sod, you may find the white "C" shaped fat little grubs laying around on the soil surface.
White grub damage is random in lawn - not usually the entire lawn - but a section. It seems grubs have their favorite spots in the lawn and that is where they concentrate. Therefore the symptoms can be confusing when you look over a nice lawn and find a random spot that appears to be water stressed. If you give the water stressed sod a tug it should lift easily from the soil. Grubs may or may not be present as they can burrow into the soil to avoid heat and drought.
Note: finding one or two grubs in a lawn does not indicate your lawn has a grub problem. A few grubs are actually beneficial. It is when they over populate an area that they cause damage. The treatments I use do not eradicate grubs – they maintain population levels below damaging levels.
White Grubs feed on roots near the soil surface severing the roots from the plant. The plant no longer has roots to absorb water and anchor it to the soil. The results is water stressed turf that can be kicked around like a throw rug on a terrazzo floor. However, by the time the symptoms occur in late fall, the damage is done, the grubs have borrowed deep into the soil and recovery is slow. Then in the spring the grubs transform into beetles and lay eggs. Then in the late summer to early fall the new generation of grubs feed on your turf’s roots and the lawn dies - again! The best control of this cycle of recovery/root pruning is to apply an insecticide long before the symptoms occur.
White Grubs are tough. For the homeowner, if you had them last year, you'll probably have them every year and most likely in the same spot. Apply a granular insecticide labeled for grubs in the evening and water in the application with .25 inches of water.
The prime time to treat for grubs in Pinellas County is June through August - while the grubs are small and easy to kill. I start treating for grubs in mid-June through August with insecticides specially engineered to be safe and effective for sub-surface pests. The treatments are broad spectrum and reduce mole crickets, weevils and ants in the lawn and landscape.
Warning: Grubs are persistent and cannot be eradicated - Do not think you can have one treatment and be done. Regular treatments every year is the best management practice. For best results hire a lawn spraying company that INCLUDES grub treatment in their regular yearly programs.
Post Damage Recovery
If you have grub damage and some life left in the turf, keep watering. The grub damaged turf is like fresh sod and needs to be watered daily to recover. A dose of insecticides will reduce the pressure on the root system and allow for quicker recovery. If the turf has turned completely brown, remove the dead turf, apply an insecticide and sod.