The white grub is the immature, larval stage of various scarab beetles, including the Japanese beetle and the masked chafer. These creamy-white, C-shaped larvae dwell beneath the soil, where they consume the roots of the turfgrass. Their feeding activity severs the plant’s connection to water and nutrients, making them a destructive lawn pest. Early and accurate identification is important for preventing widespread turf loss, which often becomes most apparent during the late summer and early fall feeding periods.
Visible Signs of Grub Damage
The initial signs of grub infestation often appear as irregular, wilted areas that resemble drought stress. Unlike grass suffering from a lack of water, these patches will not recover even with consistent irrigation. The affected turf usually turns yellowish-brown, eventually dying off in patches. This discoloration is a direct result of the grubs chewing through the root system below the surface.
If you walk across an infested area, the ground may feel unusually soft or spongy underfoot. This sensation is caused by the loss of the dense root structure that normally anchors the turf. In severe cases, the grass can be pulled back easily, lifting away from the soil like a loose piece of carpet. This occurs because the grubs have consumed nearly all the roots, leaving the sod detached from the soil base.
Wildlife Indicators of Grub Presence
Evidence of animal activity can often be the first clue that a grub population is thriving beneath the lawn. Nocturnal feeders, such as skunks and raccoons, have a highly developed sense of smell that allows them to detect the grubs. They often tear up sections of turf to access the protein source, leaving behind rolled-back sod or small, ragged trenches.
Birds, particularly crows and starlings, also prey on the larvae and may be observed frequently pecking at the lawn. These birds leave behind small, conical holes as they probe the soil looking for grubs near the surface. While this activity suggests a significant presence of grubs, it does not confirm the density or severity of the infestation. The damage caused by these predators can sometimes be more unsightly than the direct damage caused by the grubs themselves, necessitating a physical check.
The Physical Confirmation Test
A definitive diagnosis requires a direct physical inspection to confirm the grubs’ presence and density. To perform this test, select an area along the border between healthy green turf and the damaged brown patches. Using a sharp spade, cut a square section of turf measuring exactly one square foot. This precise measurement is necessary for an accurate population count.
The cut should penetrate the soil two to four inches deep, as this is the primary feeding zone for the larvae. Carefully peel back the sod flap to expose the soil and the remaining root mass. Sift through the soil and the underside of the lifted turf to locate and count all the C-shaped, creamy-white grubs. Repeat this process in several different locations across the lawn to establish an average count.
Determining If Treatment Is Necessary
The number of grubs found per square foot determines whether the population poses a significant threat to the lawn’s health. Healthy turfgrass, which is well-maintained and regularly watered, can often tolerate a population of up to five grubs per square foot without exhibiting visible damage.
An average count of six to ten grubs or more per square foot is considered the threshold for an infestation requiring treatment. If the lawn is already stressed due to drought or poor maintenance, damage may become visible even at lower grub counts.
The most effective time to apply control measures is in the late summer or early fall (August through early October). During this period, the new generation of grubs has recently hatched and is actively feeding near the soil surface, making them most susceptible to controls. Delaying treatment until spring is less effective because the larvae are larger and have moved deeper into the soil.