Grubs in My Garden Soil

Identification

• Grubs are plump, C-shaped larvae with grey or brown bodies that curl up when disturbed. Their heads are brown and usually darker than their bodies. Grubs of some beetles measure 1/2 inch long while other varieties mature at 1 inch. These pests are usually found on the top 3 inches of soil. Because moles, voles and skunks feed on grubs, their presence in your garden is often a symptom of grub infestation.

Life Cycle

• Female Japanese beetles emerge from the soil in midsummer and lay 50 to 70 eggs that hatch three weeks later. The first-stage grubs, or the larvae that hatches from the eggs, stay close to the surface of the soil and feed on the roots of plants and grass. Left to grow, the grubs develop into second- and third-stage grubs that feed on grass throughout the summer. Older grubs cause more damage to the landscape than younger grubs.

Management

• To ascertain the presence of grubs in your soil, dig out a 1-foot square of grass to a depth of 3 to 5 inches at the end summer and inspect the exposed surface for the characteristic, C-shaped larvae. Ten to 12 or more grubs per 1 square foot of soil cause severe damage to the turf and warrant immediate control. For maximum impact, treat grubs during late summer or fall, since the pests feed closest to the soil surface at that time. Depending on personal preference, adopt an organic or chemical means of control. Release commercially available nematodes in the soil that invade the bodies of grubs and release a poisonous bacterium that kills them instantly, or spread milky spores over the grass that kills feeding grubs as soon as they consume them. Alternatively, follow label directions for applying trichlorfon or carbaryl granules or formulation over grub infestations.

Prevention

• Adopt effective preventive strategies to keep grubs from infesting your soil. Avoid over-watering your lawn during the summer, since beetles lay eggs in moist soil. Follow a regular schedule of mowing and fertilizing your lawn. If you have had problems with grubs before, apply a preventive insecticide containing imidacloprid or halofenozide to the lawn before the beetles lay eggs in July.