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Past Articles Library | Organic Pest Control | Control White Grubs

WHITE GRUBS IN LAWN

White grubs are the most widespread and destructive insect pests in the cool-season and transition zones of turf grass.

DESCRIPTION

White grubs have curled C-shape bodies that vary from 1/4 to 3/4 inch (6.35 to 19 mm) long. They are creamy white with a yellow or brown head and dark hind parts. Adults vary in appearance because white grubs are the larvae of Japanese beetles, June bugs, Rose chafers, Asiatic beetles, and many others.

LIFE CYCLE

Adults emerge, mate, and lay eggs in mid-summer. The eggs are laid in the soil at 1 to 5 inches (2.5 to 12.5 cm) deep and hatch in 2-3 weeks. The grubs grow quickly and by fall most of them are nearly full-sized. Declining soil temperatures in late fall force the grubs to move deeper into the soil where they overwinter. In spring they resume feeding for about 1 month. For pupation they move deeper in the soil. Adults emerge several weeks later in late spring or early summer. A second generation emerges in late summer and feeds until autumn.

PLANTS MOST AFFECTED

All cool-season and many warm-season grasses are susceptible to white grubs.

DAMAGE

White grubs cause irregular shapes and dead brown patches of grass, especially in late spring or early fall by chewing off the roots close to the soil surface. Early lawn symptoms include gradual thinning, yellowing, wilting in spite of adequate soil moisture, and appearance of scattered, irregular dead patches. The patches increase in size and eventually join. Infested turf feels spongy underfoot and can be pulled up or rolled back easily, like a section of carpet, exposing the C-shaped white grubs. Birds, moles, raccoons, and skunks can damage lawn further by looking for grubs to eat. The adult beetles do not cause damage to grass but may be major pests of woody and herbaceous ornamentals. The damage of the annual white grubs shows up in late summer and early fall around August, September, October when the voracious feeding coincides with heat and moisture stress in the turf.

WHITE GRUB CONTROL

Prevention:

1. Cut and lift one square foot (.09 square meter) section of your lawn area. If you see more than six white grubs in the soil, it's time to apply a treatment.

2. Monitoring and sampling are keys to early diagnosis of grub problems. Watch for swarms of adult beetles skimming over the grass at dusk. Be suspicious if moles, skunks, or flocks of birds find your lawn attractive.

3. Use grass that white grubs don't feed on, called endophyte-enhance grass, which means it contains fungi that produce toxins that kill many grass-eating insects. Endophytic grasses are for lawns only - not pasture grasses - they will make livestock sick!

4. Keep your lawn healthy. Good culture will help grass better tolerate grubs and outgrow the damage.

Control:

1. Apply extra water and liquid seaweed or kelp to help the lawn outgrow any damage.

2. Apply milky spore diesase [Paenibacillus (formerly Bacillus) popilliae] in early July for long-term control. Milky disease occurs in many different strains.

3. Treating with entomopathogenic nematode (Heterorhabditis bacteriophora) can be very effective in grub suppression as a short term control.