White grubs are the larvae of various scarab beetles, such as the Japanese beetle and the masked chafer, and are destructive pests to lawns and gardens. These creamy-white, C-shaped creatures reside just below the soil surface, where they voraciously feed on plant roots. This feeding damages the root system, causing turf to wilt, turn brown, and ultimately die in patches. Effective elimination requires accurate identification, appropriate treatment selection, and precise timing.
Identifying Grub Damage and Population
Grub damage often appears as irregular, brown patches of grass that may be mistaken for drought stress. A key indicator of grub activity is when the affected turf feels soft and spongy underfoot. The most definitive sign is the ability to easily peel back sections of the dead grass like a piece of carpet because the roots have been completely severed by the feeding larvae.
Increased activity from predatory animals like skunks, raccoons, and birds digging in the lawn signals the presence of grubs. To confirm an infestation, you can perform a simple assessment by digging up a one-square-foot section of turf about two to four inches deep. If you find an average of six to ten grubs or more in this sample, the population is high enough to cause significant damage and warrants immediate treatment. Treating a lawn with a lower grub count is often unnecessary, as healthy turf can tolerate a small population without visible harm.
Biological and Cultural Control Methods
Non-chemical control methods manage grub populations using an environmentally conscious approach. Beneficial nematodes (Heterorhabditis bacteriophora (Hb) species) are microscopic roundworms that seek out and infect grubs. These nematodes enter the grub’s body through natural openings and release a symbiotic bacterium that kills the host within 48 hours.
For the nematodes to be effective, they must be applied correctly, generally in late summer or early fall when the grubs are small and feeding near the surface. The soil must be moist before application, and the nematodes should be applied in the evening or on a cloudy day, as strong sunlight neutralizes them.
Milky spore disease, caused by the bacterium Paenibacillus popilliae, targets the larvae of the Japanese beetle. When a grub ingests the milky spore, the bacteria multiply inside its body, causing a fatal disease that turns the grub a milky-white color. This method is slow-acting and can take two to four years to establish, but once established, it provides long-term control, sometimes lasting 10 to 20 years. Cultural controls also reduce grub appeal; beetles prefer to lay eggs in well-watered turf, so reducing irrigation during the peak egg-laying period in summer makes the lawn less attractive.
Applying Synthetic Chemical Treatments
Synthetic chemical treatments are categorized into two types: preventative and curative, defined by different active ingredients and application timings. Preventative insecticides stop grubs before they hatch and grow large enough to cause damage. Common active ingredients for prevention include Imidacloprid and Chlorantraniliprole.
Imidacloprid and similar neonicotinoids are highly effective against newly hatched, small grubs and are typically applied in June or July. Chlorantraniliprole is less water-soluble and offers a wider application window, often from early spring (April or May) up until mid-July, as it takes longer to move into the root zone.
Curative treatments eliminate active infestations and contain fast-acting ingredients like Carbaryl or Trichlorfon. These products are short-lived in the soil and are generally applied in late summer or early fall when grubs are actively feeding near the surface. For both treatments, the chemical must be watered into the soil immediately after application (about one-half inch of water) to move the active ingredient down to the root zone. Safety precautions are necessary; follow label instructions exactly for proper dosage and handling.
Optimal Timing and Long-Term Prevention
Successful grub control hinges on understanding the beetle’s one-year life cycle, which dictates treatment timing. Adult beetles emerge in early summer (June and July) to mate and lay eggs. The eggs hatch into small, newly hatched grubs from late July through August, which are the most vulnerable to treatment.
This late summer to early fall period (August to September) is the optimal window for applying curative treatments or beneficial nematodes, as grubs are actively feeding near the surface. If not killed, they move deeper into the soil to overwinter as temperatures drop. Preventative treatments, such as those with Imidacloprid, are timed for late spring or early summer to ensure the chemical is present when the eggs hatch.
Long-term prevention is achieved by maintaining a dense, healthy lawn, which naturally deters beetles from laying eggs. Mowing grass at a higher setting, such as three inches or more, encourages deeper root growth that can withstand minor grub feeding. Proper watering, deep and infrequent instead of shallow and frequent, also promotes a robust root system that is more resilient to damage.