White grubs are the larvae of several species of scarab beetles, including the Japanese beetle, masked chafer, and European chafer. These small, creamy-white, C-shaped insects live in the soil and feed on the root systems of turfgrass. Their feeding severs grass roots from the soil, leading to extensive, visible damage to the lawn. Early detection is the most effective way to manage an infestation before significant portions of the lawn are destroyed.
Recognizing the Visible Signs of Infestation
Initial signs of a grub problem often manifest as irregular, dead patches of grass appearing within a healthy lawn. These patches may first resemble drought stress, but unlike dry spots, they do not recover even with adequate watering. The grass begins to thin, yellow, and eventually turns brown because the roots have been eaten away.
The most distinct indicator of severe root damage is the texture of the turf when you walk on it. Areas of the lawn will feel noticeably loose and spongy underfoot. If the infestation is significant, the grass in the affected areas can be lifted or rolled back easily, much like peeling up a piece of sod, because the root structure holding it to the soil is gone.
Increased activity from local wildlife suggests the presence of a subsurface pest. Animals such as raccoons, skunks, and birds actively dig and tear up the lawn to feed on the grubs. The sudden appearance of small, torn-up areas of turf or holes in the soil is a strong visual cue that a substantial food source, likely grubs, is present.
Timing Your Search with the Grub Life Cycle
The effectiveness of finding grubs depends directly on knowing when they are most active and closest to the soil surface. White grubs generally have a one-year life cycle, and their location in the soil changes with the seasons and temperature. They are easiest to find when they are young and feeding aggressively near the grass roots.
This prime sampling window typically occurs during the late summer and early fall, particularly in August and September. During this period, the eggs laid by adult beetles in mid-summer have hatched, and the young larvae begin their most damaging phase of feeding. The young grubs are concentrated within the top few inches of the soil, making them accessible for inspection.
As the soil temperatures cool in late fall, the grubs migrate downward, sometimes going several inches deep to burrow below the frost line. They remain mostly inactive during the cold months, which makes them difficult to find through surface sampling. The most reliable time to quantify their population is during the late-summer feeding stage, though they move closer to the surface in the spring before pupating.
Step-by-Step Physical Sampling Methods
To confirm the presence and density of grubs, a systematic physical sampling method is required. Begin by identifying areas that show visible signs of damage, such as brown patches or spongy-feeling turf, but focus your inspection on the border between the healthy and damaged grass. This boundary is where the grubs are likely still actively feeding.
Using a spade or shovel, cut a square section of turf measuring one square foot. The cut should penetrate the soil to a depth of two to four inches, as this is the zone where the grubs feed on the grass roots. Carefully lift and peel back the square of sod to expose the soil and the underside of the turf.
Once the soil is exposed, closely examine the loose soil, the root mass attached to the sod, and the thatch layer for the creamy-white, C-shaped larvae. Count the total number of grubs found within that one-square-foot sample area. It is important to repeat this sampling procedure in several suspicious locations across the lawn to get an accurate estimate of the overall population.
Finding a few grubs is normal and generally does not cause significant damage. However, a count of six to ten grubs or more per square foot is a common threshold that indicates a need for management. After counting, the soil and turf slice should be carefully replaced and pressed firmly back into the ground, and watering the patched area helps the roots re-establish quickly.