Lawn grubs are a common and destructive pest, representing the larval stage of various scarab beetles. These C-shaped, white larvae live beneath the soil surface, where they feed voraciously on grass roots. This feeding activity severs the connection between the turf and the soil, causing significant damage that leads to dead patches across a lawn. Fortunately, you can manage and eliminate these pests without resorting to harsh chemical treatments. Understanding the grub life cycle and employing biological and cultural practices allows you to restore your lawn naturally.
Recognizing the Signs of Grubs
Before applying any treatment, confirm that a grub infestation is the cause of your lawn trouble. The first indicator is the appearance of irregular, brown patches of grass that resemble drought damage. If these patches feel soft and spongy underfoot, it is often a sign of root damage.
A definitive test involves a pull test on the affected turf. Because the grubs have severed the root system, the grass will lift easily from the soil, often rolling back like loose carpet. Beneath the lifted sod, you may see the white, C-shaped larvae directly.
Another strong indication of a grub problem is increased activity from natural predators. Animals such as raccoons, skunks, and birds will actively dig up your lawn to feast on the grubs. If you find more than six grubs per square foot of soil, the population warrants immediate action.
Timing Your Natural Treatment for Maximum Effect
Effective grub control depends on timing, which must align with the pest’s annual life cycle. Adult beetles lay eggs in the soil during early to mid-summer, and these hatch into tiny grubs shortly after. The newly hatched larvae remain near the surface, actively feeding on grassroots from late summer through early fall.
This period, typically August to October, is the most effective window for applying natural treatments. The young grubs are easily targeted by biological controls because they are feeding consistently near the soil surface. Spring treatment is less effective because the grubs are large and have moved deeper into the soil to prepare for pupation. Focusing efforts on late summer and early fall targets the new generation before they cause extensive damage.
Utilizing Biological Controls
Natural methods for grub elimination involve introducing biological agents into the soil. These living controls target the larvae without harming people, pets, or beneficial insects. The two primary biological treatments are beneficial nematodes and Milky Spore powder.
Beneficial nematodes, specifically Heterorhabditis bacteriophora (Hb), are microscopic, soil-dwelling roundworms that actively hunt for grubs. These “cruiser” types move aggressively through the soil to locate prey. Once a grub is found, the nematode enters the host and releases a symbiotic bacterium that is lethal, typically killing the grub within 48 to 72 hours.
For successful application, the soil must be moist before and after treatment to facilitate nematode movement and survival. Since they are living organisms, apply them in the early morning, evening, or on an overcast day to protect them from ultraviolet light. After mixing the product with water, apply the solution using a hose-end or pump sprayer, then water lightly to wash the nematodes into the soil.
Milky Spore is a long-term biological treatment containing the naturally occurring bacterium Paenibacillus popilliae. This bacterium is specific to the larvae of the Japanese beetle. When a grub ingests the spores while feeding on grass roots, the bacterium multiplies inside its body, causing a fatal disease.
As the infected grub decomposes, it releases billions of new spores back into the soil, slowly building up the disease concentration. Milky Spore is a one-time application that can provide control for 10 to 20 years. However, it is slow-acting and may take two to three seasons to build up effective levels. For faster results, some apply both Milky Spore and H. bacteriophora nematodes simultaneously.
Adjusting Lawn Care for Long-Term Prevention
Preventing future grub infestations relies on modifying lawn maintenance practices to make the environment less appealing for adult beetles to lay eggs. Cultural practices that encourage deep root growth also allow the grass to tolerate minor grub feeding with less noticeable damage.
Adjusting your watering schedule is a key preventative measure. Adult beetles, particularly the Japanese beetle, prefer to lay eggs in consistently moist soil, as the eggs require moisture to survive. During the peak egg-laying season in mid-summer, allow your lawn to dry out slightly by watering infrequently but deeply. This encourages deeper grass roots, making them more resilient to surface-level grub activity.
The height at which you mow your lawn also plays a role in prevention. Maintaining a higher mowing height, typically between 3 and 4 inches, helps to shade the soil surface. Shaded, cooler soil is less attractive to egg-laying adult beetles than bare, warm soil.
Supporting grass vigor through proper fertilization minimizes the visual impact of grub feeding. Using organic or slow-release fertilizers helps maintain steady, robust growth. This ensures the grass can quickly repair and recover from root damage, allowing a healthy lawn to better withstand infestation stress.