Typical lawn grubs, often called white grubs, are white, C-shaped beetle larvae about a half-inch long. A grub may be the larvae of the masked chafer or European chafer, Japanese beetle, or other beetle species. Lawn grubs have soft bodies with legs near the head.
What Is a Grub?
A grub is the soft and wormlike larva of an insect, such as a beetle, that feeds on grassroots (and organic matter in the soil), causing sections of grass in the lawn to die.
How to Know if You Have Lawn Grubs
Grub damage can appear in 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.
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, and Japanese beetles can be seen flying during the day, feeding on ornamentals, for example.
Types of Lawn Grub Control
An integrated pest management (IPM) program—also known as integrated pest control (IPC)—uses a combination of methods to control garden pests. It incorporates preventative measures, regular monitoring for pests, environmentally friendly control methods, and the responsible use of pesticides.
An active IPM program is the best plan for dealing with any lawn pests. Periodic scouting is the best defense, especially late in the summer when grub damage is greatest.
If you have cut into the soil and determined that an outbreak has occurred, an insecticide such as Dylox could be used. (Insecticides such as Merit help prevent grubs while in the egg stage.) It's also best to wait until a new lawn is established before applying grub killer chemicals.
Insecticides are dangerous and best handled by a licensed pesticide applicator. Insecticides also harm pollinators, such as bees, that feed off of blooming clover weeds in a lawn. Protect pollinators by applying insecticide when weeds are not in bloom, or mow down blooms before application so bees don't ingest the toxins.
Keeping your soil healthy with the right type of organic matter can deter grubs.
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.
Beetles lay their eggs in moist, irrigated soil. A natural preventative method is to avoid watering your lawn during midsummer dry spells. The lawn may turn brown and go dormant, but a grub problem is less likely.
How to Repair Lawn 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. Here are the basic steps:
- Rake and remove loose and dead patches of lawn.
- Aerate your lawn.
- Reseed your lawn.
- Adequately water seeds to establish roots.
- Keep an eye on flipped pieces of new lawn; just flip them back over.
What Do Grubs Turn Into?
Grubs eventually turn into adult scarab beetles, which emerge from the soil to mate and lay eggs. The adult beetles don't do much damage to yards. The serious damage comes to your lawn, ornamental grasses, and flowers when the adults hatch their eggs that turn into these problematic, hungry little grubs. Scarab beetles, which have stout, metallic bodies, will emerge to mate and lay eggs in early summer to midsummer.
Dung beetles, which are scarab beetles, are not dangerous to your yard since they feed on feces and are actually beneficial to soil. However, there are a few different types of pesky scarab beetles that grubs can turn into, including:
- Asiatic garden beetles
- Black turfgrass ataenius
- European chafers
- Green June beetles (June bugs)
- Japanese beetles
- Northern masked chafers
- Oriental beetles
- Southern masked chafers
Billbugs are not scarab beetles, but grubs can also turn into these destructive pests. Billbugs are prevalent in most of the United States except in Florida. Adult billbugs are creamy or brown but not metallic. They chew holes in grass where they lay their eggs. Adults and their larvae are equally damaging since they feed off the grass roots.