What Are Lawn Grubs?
Lawn grubs, also known as white grubs, are small white creatures that curl up into a distinctive C shape when disturbed. The grub worm is the larval form of several types of scarab beetles including Oriental beetles, Japanese beetles, chafer beetles and green June beetles.
When lawn grubs are active in an area, you can find them a couple of inches below the surface of the soil. As winter approaches, they burrow deeper, between 4 and 8 inches beneath the surface.
Grubs typically damage lawns by feeding on grass roots. They develop into beetles, which feed on foliage and flowers. The female beetles lay their eggs in the lawn, and the eggs hatch into grubs during the summer. The young grubs begin feeding and continue into the fall. This is when they do the most damage. They become inactive as winter approaches but become active and begin feeding again in the spring. The life cycle of most scarab beetles is one year.
Do You Need Lawn Grub Control?
There are several types of damage in the lawn that may indicate grubs. Brown patches that don't green up in the spring may be the result of grubs feeding the previous fall. In late summer and fall, randomly shaped dead patches may indicate grubs.
Birds, raccoons, skunks, moles and other small animals may tear up areas of your lawn at night looking for grubs. Turf that feels spongy or that lifts easily to reveal damaged roots or no roots at all may also be evidence of grub damage.
These symptoms can also signify other lawn conditions. Checking the soil for grubs is the only way to confirm that your lawn has grubs and to determine if you need lawn pest control.
- Make cuts 6 to 12 inches long and about 3 inches deep on three sides of a patch of grass.
- Peel back the turf and look for grubs.
- Check several areas and estimate the number of grubs per square foot of your lawn.
- Once you've finished checking for grubs, replace the turf.
Having five or fewer grubs per square foot isn't a problem for a healthy lawn. If you find six or more per square foot, you may want to treat the most visibly damaged areas of your lawn. You may also want to get rid of the grubs if animals are digging up your lawn looking for them. Ten or more grubs per square foot will likely cause noticeable damage and require thorough treatment.
Beetles flying over your lawn or a neighbor's lawn during the summer may be a hint that you'll find grubs later in the year. A well-watered, unshaded lawn can invite grub activity. There will be a better chance that beetles will lay eggs and grubs will develop if you have moist soil.
How to Control Grubs in Grass
Some grub control methods are simply good lawn care practices. A healthy, thick lawn discourages beetles and grubs, and has a deep root system that'll be more tolerant of damage that does occur. See 8 Easy Tips for the Perfect Lawn for ideas on how to maintain a healthy lawn.
Insecticides
Insecticides are available to help you control grubs. Curative products with active ingredients, such as trichlorfon, are designed to kill grubs at any stage of development.
If you've had grub problems the previous year and expect them this year, a preventative insecticide like one containing chlorantraniliprole or imidacloprid can be effective. Preventative products kill young grubs currently hatching, helping you avoid damage later on in the year.
Application timing impacts insecticide effectiveness and differs depending on the chemical so follow the recommendations on the package. Pay attention to the types of insects that the insecticide will kill so you don't accidentally exterminate beneficial species like mantis and dragonflies.
Mow before grub worm insecticide treatment to help the chemical reach the soil faster. Dethatch and aerate your lawn to also help get the chemical to the grubs.
Grub Worm Insecticide Alternatives
There are other treatment options you can consider which don't include the use of pesticides.
Milky Spore
Milky spore (Bacillus popilliae) is a bacteria that can naturally kill Japanese beetle grubs. However, it won't work against the larva of other types of beetles.
Natural Predators
Encouraging visits from grub worm predators — such as ants, wasps, ground beetles and birds — can be effective in managing the grub population.
Dormant Grass
Letting your lawn go dormant during the summer can prevent damage from grubs in the grass because the dry soil will be less attractive for egg laying.
When using lawn treatments or lawn-care products, always follow package directions regarding proper clothing, protective equipment, application procedures and safety precautions.
Repairing Lawn Grub Damage
Once you've found an effective method of lawn grub control, you need to repair the damage they caused. Some areas may recover simply with proper care. Just clear away the dead material and water the damaged area.
See How to Plant Grass Seed for tips on selecting grass and instructions on seeding.
A grub-tolerant variety of grass is a great option if you frequently encounter lawn grub damage. No grass is grubproof, but grass species with deep root systems and drought tolerance can handle grub damage better.
Drought-tolerant grass also fares better in the dry conditions that discourage grubs. Warm-season grasses are more tolerant of grubs than cool-season varieties. Of the cool-season grasses, tall fescue grass is the most grub tolerant.
Learn how to Choose the Right Grass for Your Lawn with this article.