Is it grubs? The 30-second test.

White grubs are the larvae of beetles — June beetles, Japanese beetles and a few others. They live just under the surface and eat grass roots. By the time you see damage, they’ve been eating for weeks.

Signs it might be grubs

• Irregular brown patches in late summer or early fall, even with good watering
• The turf lifts up like a loose carpet because there are no roots holding it
• Skunks, raccoons, armadillos or birds digging up the lawn overnight

The 30-second test

1. Pick a spot at the edge of a brown area, where the grass is still partly green.
2. With a shovel, cut a square about one foot by one foot on three sides, two inches deep.
3. Fold the flap back like a page and look at the soil and roots.
4. Count the C-shaped white grubs.
5. Press the flap back down and water it.

If you found a lot

Late summer and early fall is when grubs are small and close to the surface, which is the best time for a curative product (trichlorfon or carbaryl are common). Water it in right after applying so it reaches the root zone.

If you found only a few

Don’t treat. Look for another cause — disease, drought or dog spots are more likely.

Prevent next year

A preventive grub control (chlorantraniliprole is common and low-toxicity) applied from late spring into early summer stops the next generation before it hatches. If you’ve had grubs two years in a row, make this a yearly step.