Grubs are the soft-bodied, C-shaped larval stage of various scarab beetles, including the Japanese beetle and European chafer. These insects spend a significant portion of their life cycle beneath the soil surface, where they feed on the roots that anchor turfgrass. An unchecked infestation can quickly compromise the health and appearance of an entire lawn, leading to widespread damage before the problem is even visible above ground. Understanding how grubs damage the lawn and how to confirm their presence is the first step toward effective management.
How Grubs Cause Lawn Damage
Grubs consume the fine root hairs and the root system. By severing the connection between the grass blades and the soil, the grubs eliminate the plant’s ability to absorb water and nutrients. This root-feeding activity leads to noticeable symptoms that are often mistaken for drought stress, such as irregular patches of wilting, discolored grass that fails to green up even after watering.
When a significant portion of the root system is consumed, the turf loses its anchoring to the soil. Walking across an infested area may cause the ground to feel unusually soft or spongy underfoot due to the loose, unattached layer of sod. In cases of severe feeding, the turf can be easily lifted or rolled back like a piece of carpet, revealing the white grubs underneath. This level of damage often peaks in late summer and early fall when the grubs are largest and feeding most actively.
Identifying an Active Infestation
Confirming the presence of a grub problem requires a physical inspection of the soil, as the visual symptoms alone can be misleading. To accurately diagnose an active infestation, a small square foot section of turf needs to be cut on three sides and peeled back like a flap. This allows for a direct examination of the soil and the remaining root zone, where the grubs congregate.
If more than six to ten grubs are found within that single square foot area, the population is considered high enough to warrant treatment, as this threshold indicates a strong potential for visible lawn damage. Another important diagnostic sign is the increased activity of predatory animals such as raccoons, skunks, and birds, which will tear up the turf to forage for the grubs. These animals are drawn to the concentrated food source, often causing damage to the lawn in their search.
Effective Grub Control Strategies
Grub control strategies are typically divided into two categories: preventative and curative, each with specific timing and product requirements. Preventative treatments are the preferred method and rely on applying a product before the damage occurs, targeting the newly hatched, small larvae. These applications, often containing ingredients like neonicotinoids, are made in late spring or early summer to create a long-lasting barrier in the root zone. This proactive approach is highly effective because the young grubs are most susceptible to the chemical shortly after they hatch in mid-summer.
Curative treatments are necessary when a high population is discovered later in the season, typically in late summer or fall when damage becomes visible. These products, which often contain active ingredients like carbaryl or trichlorfon, are fast-acting but are less effective than preventative measures because the grubs are larger and harder to kill. For both chemical types, it is necessary to water the lawn immediately after application to move the product down into the soil where the grubs are feeding.
For homeowners seeking alternative methods, biological controls offer a more environmentally focused solution, though they require specific application conditions. Beneficial nematodes are microscopic organisms that parasitize and kill grubs, and they should be applied when soil temperatures are between 50 and 70 degrees Fahrenheit. They must be applied on a cloudy day or in the evening and watered in thoroughly, as they are susceptible to direct sunlight and desiccation.
Another biological option is Milky Spore, a bacterium that specifically targets Japanese beetle grubs, but its establishment is a gradual process. The spores are ingested by the feeding grubs, multiply inside them, and are released back into the soil upon the grub’s decomposition, slowly building up the disease in the area. Although it can take several years to fully inoculate the soil, a single successful application may provide long-term control against this specific grub species.
Cultural practices promote turf health and minimize the impact of grubs. Maintaining deep, healthy grass roots through proper mowing height and appropriate watering can help the lawn tolerate a moderate grub population without showing visible damage. Reducing excessive watering in mid-summer makes the lawn less attractive to adult beetles looking for a moist location to lay their eggs.