Lawn grubs, often called white grubs, are the immature, larval stage of several types of beetles, including Japanese beetles, June bugs, and chafers. These pests reside just beneath the soil surface, feeding voraciously on the delicate roots of your grass. As grubs consume the root system, they sever the turf’s connection to the soil, preventing the grass from absorbing necessary water and nutrients. This root destruction compromises the lawn’s health and stability, leading to visible damage. Determining the presence of these subsurface pests requires observing outward signs and performing a physical inspection.
Visual Indicators of Grub Activity
The initial signs of a grub problem frequently become apparent in the late summer or early fall, when newly hatched larvae begin their active feeding period. The most common indication is the appearance of irregularly shaped, brown, or dead patches of grass that do not respond to watering. Unlike drought stress, which affects the lawn uniformly, grub damage appears in sporadic, isolated areas that may grow larger as feeding continues.
A secondary sign of root damage is a change in the turf’s texture, causing the lawn to feel soft or spongy underfoot. When grubs eat away the roots, the grass loses its anchor to the soil, creating a loose, bouncy sensation. In severe cases, the turf can be easily pulled back, sometimes rolling up like a carpet because the root structure has been compromised.
Increased activity from predatory wildlife also serves as a strong visual clue that grubs are present beneath the surface. Animals such as skunks, raccoons, and birds feed on these larvae and actively tear up the lawn to find them. The presence of small, random holes or overturned sections of turf from foraging animals is often a reliable indicator of a concentrated grub population.
Direct Inspection Methods
Confirming a suspected grub infestation requires a direct inspection beneath the turf surface. The most reliable method is the “trench test,” which involves carefully cutting and lifting a small section of the lawn. Use a spade or shovel to cut a square of turf approximately one square foot in size and two to four inches deep.
The turf sample should be carefully lifted and examined, focusing on the soil just beneath the root zone. Grubs are easily identifiable by their creamy white color, plump, C-shaped bodies, and distinct brown heads. The best time for this inspection is late summer through early fall, as the grubs are larger and actively feeding near the soil surface.
If the turf easily peels back or lifts away with minimal resistance, it confirms the root system has been destroyed. Carefully break apart the soil and root mass of the lifted sample to count the grubs present. After the inspection, the square of sod can be placed back into the hole, patted down, and watered thoroughly to encourage re-rooting.
Counting Grubs and Infestation Severity
The final step is assessing the severity of the infestation by counting the grubs in the sample area. A healthy lawn can tolerate a small number of grubs; finding one or two larvae per square foot is considered normal and does not require immediate action. The grass’s extensive root system can withstand minimal feeding without showing outward symptoms.
A count of five to ten grubs per square foot is considered the threshold for a damaging population that warrants treatment. At this density, the grubs consume enough roots to significantly weaken the turf, leading to visible brown patches and spongy texture. The exact number that causes visible damage can vary based on the type of grass and its overall health.
If the grub count exceeds ten per square foot, the infestation is severe and likely responsible for noticeable turf loss. This high concentration of larvae indicates a need for intervention, as root destruction will continue until the population is reduced. Counting the grubs in multiple one-square-foot samples across the lawn provides the necessary data to determine the extent of the problem.