Grubs are the larval stage of various beetles, such as Japanese beetles, June beetles, and masked chafers. These C-shaped insects spend most of their existence beneath the soil surface, causing destruction to lawns. Their presence often leads to the failure of reseeding projects for homeowners.
The Truth About Grub Feeding Habits
Grubs do not typically consume grass seed itself; their destructive focus is on the established root system of the grass plant. These larvae are primarily root feeders, devouring the fine, fibrous roots that anchor the turf and absorb water and nutrients. The damage is a direct result of them severing the connection between the grass blades and the soil.
For a newly seeded lawn, the outcome is the same as if the seed were eaten, but the mechanism is different. New seedlings develop fragile, shallow root structures that are easily clipped by grubs. When these tender roots are eaten, the new grass quickly wilts and dies because it cannot access moisture, leading to reseeding failures.
Recognizing and Confirming Grub Damage
Grub damage often first appears as irregular patches of brown, wilting grass, which homeowners may mistake for drought stress. These damaged areas will feel soft and spongy underfoot because the turf is no longer firmly connected to the soil.
A simple “tugging test” can help confirm a grub problem: if you can easily pull up a patch of grass like a piece of loose carpet, the roots have been eaten away. The “shovel test” involves digging up a square foot of turf in a damaged area; if a count reveals six to ten or more grubs, treatment is warranted. Secondary signs of an infestation include activity from vertebrate predators like skunks, raccoons, and birds, which dig up the lawn to forage for the grubs.
Timing is Everything: The Grub Life Cycle
The most common lawn grubs, like the Japanese beetle, typically have a one-year life cycle that dictates the timing of control measures. Adult beetles emerge in early to mid-summer to mate, laying their eggs in the soil, usually in late June and July. The eggs hatch into tiny, first-stage grubs, known as instars, within a couple of weeks.
These small grubs begin feeding heavily on grass roots in late summer and early fall, which is when the most visible damage appears. As soil temperatures drop in late autumn, the grubs stop feeding and burrow deeper into the soil to overwinter. They return to the root zone to feed briefly in the spring before pupating and transforming into adult beetles, restarting the cycle.
Effective Strategies for Grub Control
Controlling grubs involves two distinct approaches: preventative and curative. Preventative treatments are applied in early summer, typically June or July, before the eggs hatch. These systemic insecticides are absorbed by the grass roots and kill the grubs shortly after they hatch, making this the most effective strategy.
Curative treatments are reserved for active infestations found in late summer or early fall when the grubs are present and feeding. These fast-acting contact insecticides kill the larger grubs on contact. Curative applications are less efficient because the grubs are larger and have already caused turf damage.
When reseeding a damaged area, apply a curative treatment two to three weeks before planting the new grass seed. This buffer period is important because some chemical controls can interfere with seed germination or harm tender seedlings.
Biological controls, such as beneficial nematodes, offer an alternative, targeting the grubs in the soil. Integrating proper lawn care, such as deep and infrequent watering, can also make the turf more resilient by encouraging a deeper root system.