Typical lawn grubs, often called white grubs, are white, 'C'-shaped larvae of beetles about a half-inch in length. A grub may be the larvae of the masked chafer, European chafer (pictured), Japanese beetle or other beetle species. Lawn grubs have soft bodies with legs near the head. They feed on grass roots (and organic matter in the soil), causing sections of grass in the lawn to die. Grubs eventually turn into adult beetles and emerge from soil to mate and lay eggs, which hatch into more grubs.
How Do I Know if I Have Grubs?
If you can pull sod away from the ground, the root system may have been eaten by grubs. Cut into the soil and look for their presence. More than 10 grubs per square foot is a red flag.
The presence of grubs may be an indication that beetles are laying eggs in your lawn. Tan-colored chafer beetles are active just after sundown; Japanese beetles can be seen flying during the day, feeding on ornamentals.
Grub damage can appear two ways. First, small irregular patches of a lawn will appear brown, dry and wilted. Damage also occurs when raccoons and crows tear up the lawn to feed on grubs. Both types of damage can be extensive during a severe outbreak.
Dealing with Grubs
An active IPM program is the best plan for dealing with any lawn pest. Periodic scouting is the best defense, especially in late in the summer when grub damage is greatest.
If you have cut into the soil and determined that an outbreak has occurred (indicated by more than 10 grubs per square foot), an insecticide such as Dylox could be used. (Insecticides such as Merit help prevent grubs while in the egg stage.) Insecticides are dangerous and best handled by a licensed pesticide applicator.
Is There an Organic Product that Can Kill Grubs?
The best organic grub control is prevention. Beetles lay their eggs in moist, irrigated soil. A natural alternative is to avoid watering during mid-summer dry spells. The lawn may turn brown and go dormant, but a grub problem is less likely.
Healthy soil and Integrated Pest Management give you the upper hand in grub defense.
Milky spore is a naturally occurring bacterium that can help control grub populations in USDA weather zones 7 through 10. When the soil is inoculated with milky spore, the grubs inadvertently eat the spores while feeding and die, releasing millions of more spores. It can be a lengthy process, but it is organic.
Some nematodes are natural enemies of white grubs. There are many different types of nematodes, some beneficial and others not. Hb nematodes are watered into the soil to introduce a natural grub predator.
How to Repair Grub Damage
Because the grubs feed on the roots, grass will need to be started from scratch. Just treat the area like any other bare patch repair and be certain to keep the seed moist while germinating.