Beetles - Grubs

Grubs are the larvae of beetles. They are between 3/4" and 1 1/2" in length, white to grayish with brown heads, and commonly curl into a "C" shape when disturbed. They feed underground on roots (particularly those of turf grasses) for one year or more, depending on the species. Damage caused by grubs begins in early fall, when the larvae begin to hatch from eggs laid in July and August. The larvae feed on roots until the ground freezes in late fall, then burrow more deeply underground to stay warm. In spring, they return to the surface and resume feeding on roots.

Damaged sections of lawn appear burned and can be lifted with ease; upon doing so the culprits will be exposed. From your lawn, grubs may move into your vegetable garden and proceed to eat roots and bases of plants, especially in early summer. They can cripple or ruin plants without being detected. Vulnerable crops include young apple trees, blackberries, corn, onions, potatoes and strawberries. Other symptoms of infestation include the presence of moles, shrews, chipmunks, skunks, raccoons, and birds, all of whom relish grubs and will dig up your lawn or garden in search of a good snack. Large numbers of adult beetles being attracted to lights at night may also signal a problem.

Use of parasitic nematodes is a promising method of controlling grubs. The nematodes inject a killing bacteria into grubs but leave earthworms and other beneficial soil life unharmed. Up to four applications may be required. Milky spore disease or Bacillus popilliae is an effective long term control. While it is expensive and takes 3 to 5 years to be completely effective, an application can last 10 years or more when properly applied.

Specific recommendations for lawns. Grub problems can be prevented or reduced by keeping your lawn healthy with proper watering and fertilizing. Keep in mind that adult beetles lay their eggs in July and August and prefer moist, lush lawns; keep the lawn on the dry side during this period and mow it high. While your lawn may briefly go dormant without lots of water, its roots won't be damaged and it therefore will recover quickly. Weigh this against the potential for burned brown patches later in the season due to grub damage, and remember that weeds can easily establish themselves where turf grass root systems have been destroyed by grubs.

Specific recommendations for gardens. Reduce overwintering grubs by removing all old plants and overgrown weeds as you harvest each crop in the fall. Cultivate the bare soil thoroughly to a depth of 6 to 8 inches. 2 to 3 weeks later, cultivate the soil shallowly to a depth of about 2". At this point you can plant a cover crop or lay down 4" to 6" of winter mulch. In early spring, about 2 weeks prior to planting, give the garden another shallow cultivation to about 2". Upon planting, give soil a final cultivation. This frequent tilling will expose overwintering grubs to cold and to their predators. Since crows, robins and starlings are avid grub eaters, their presence in the garden prior to cultivation should be encouraged.

Specific grubs

Other images

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Grub of an eastern hercules beetle, Dynastes tityus, the largest beetle (Coleoptera) in North America, found in firewood and feeds only on dead wood.
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Grub of an eastern hercules beetle, Dynastes tityus (Coleoptera), found in firewood. No control is needed as this grub feeds only on dead wood.
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Grub of a eastern hercules beetle, Dynastes tityus (Coleoptera), found in firewood. No control is needed as this grub feeds only on dead wood.
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Holes in firewood caused by a Hercules beetle, Dynastes tityus. These beetle grubs (Coleoptera) are part of the decay process and feed only on dead wood.
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Feeding galleries in firewood caused by a Hercules beetle, Dynastes tityus (Coleoptera).