If your lawn in the Northeast starts showing brown patches in early fall, chances are grubs are the culprits. These small, C-shaped white larvae can do major damage beneath the surface before you even know they’re there. In this Healthy Lawns segment, Dr. Jim explains why understanding their lifecycle is the first step to effective prevention and control.

What Are Grubs?

Grubs are the larval (or worm) stage of various beetles common to our region. The most notorious of these is the Japanese beetle, easily recognized by its metallic green body and copper-colored wings. While adult beetles feast on flowers and foliage—especially roses—their young, hidden underground, are busy feeding on the roots of your grass.

Other beetles also produce grubs, but Japanese beetles are the primary cause of grub-related lawn damage in the Northeast.

The Lifecycle: From Beetle to Beetle Again

1. Summer (July–August): Egg Laying
   During the warm summer months, adult beetles lay their eggs in your lawn’s soil. They prefer moist conditions, which help ensure their eggs will hatch successfully.
2. Late Summer to Fall: Grub Feeding Begins
   When soil moisture is right, the eggs hatch into tiny white grubs. At first, they’re too small to notice, but as they feed on grass roots, they grow—eventually reaching about an inch long. Most grub damage occurs in early to mid-fall, when these larvae are actively feeding and weakening your turf from below.
3. Winter: Going Deep to Survive
   As temperatures drop, grubs burrow deeper into the soil to avoid freezing. They remain dormant during the coldest months, waiting for spring.
4. Spring: The Return to the Surface
   When soil temperatures rise, grubs move back up toward the root zone and begin feeding again, though not as aggressively as in the fall. Soon after, they pupate—transforming into adult beetles—and emerge to start the cycle all over again.

Signs of Grub Damage

• Soft, spongy turf that easily lifts like a carpet
• Irregular brown patches in late summer or early fall
• Birds, skunks, or raccoons digging up your lawn in search of grubs

How to Protect Your Lawn

The best defense against grubs is timing your lawn treatments around their lifecycle. Preventive grub control products applied in late spring to early summer can stop eggs from hatching. If you already see damage, curative treatments in early fall can help reduce active grub populations.

Healthy lawns start below the surface. By understanding the grub lifecycle, you can stop these underground invaders before they cause lasting damage and keep your lawn lush and green year after year..

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