White grubs

Should I be concerned?

Grubs feed on the roots of many plants, but like the fibrous roots of lawn grass best. As the roots are destroyed, turf will wilt and turn brown. Grubs also feed on potatoes and carrots in the garden. They cut the main stems or roots of plants below the soil surface, and tunnel into tubers and freshly rooted plants.

How do I know if I have a problem?

Affected areas will feel soft and spongy to walk on, and turf in these spots can be lifted up with ease. Carefully fold back the turf and note the number of grubs exposed. Eight to 10 grubs per square foot can damage a lawn.

Damage is most severe in the spring and fall when moisture levels in the soil are high. During drier periods, the eggs may be killed and surviving larvae can be found deeper in the soil. Extremely dry summers destroy many eggs and newly hatched grubs. Mature grubs can be found near the surface in late summer and early fall.

Often, skunks and other small mammals will pull back the turf to feed on grubs in the spring or fall. This secondary damage to your lawn, as well as flocks of starlings and blackbirds feeding on your lawn, are signs of a grub infestation. If you have any of these natural predators digging at your grass, check for white grubs. Many people notice these indicators first.

How can I get rid of grubs?

Lawn care

The best thing you can do is to make sure your lawn is healthy before any problems happen. If you can, dig or till your land one year before you seed it or lay sod. Remove old plants and weeds, then rake/de-thatch your lawn or cultivate the soil thoroughly to expose any grubs to their predators and the weather.

Healthy, vigorously growing lawns can tolerate more grub feeding than stressed lawns, because damage to one root is made up for by others. Remove excessive thatch, and aerate compacted soil areas to ensure proper drainage. A soil aerator with spikes or spiked sandals can also help kill some of the grubs.

Beetles prefer to lay eggs in closely cropped lawns, so raise your summer mowing height to 6 to 8 cm (2.5 to 3 inches). Leave lawn clippings after mowing, because their slow release of nitrogen encourages micro-organisms to break down the thatch. Use fertilizer with high potassium and enough nitrogen.

If you notice grubs during the warm, dry periods of the growing season, water and fertilize your lawn to strengthen it and make up for the root feeding damage. Apply a top dressing of sand and manure and overseed with grass. Deep, infrequent watering encourages deep-rooted, drought-tolerant lawns. Water no more than once a week, and water until at least 2 cm (1 inch) of water collects in a container placed on your lawn or for about one hour.

Population control

You can hand pick adult beetles or vacuum them using a small vacuum with a disposable bag. You can also shake beetles from plants and collect them in a cloth, placed directly below the plant. For best results, collect the beetles early in the morning when they are still sluggish. Put beetles in soapy water to kill them.

Predators

Beneficial insects like ants prey on the eggs of June bugs. Certain parasitic wasps and flies also help keep June bug or Japanese beetle populations in check. Some of these are specific to a single insect, but others will control several pests in an area. Bird houses attract natural predators (like starlings and blackbirds) that feed on white grubs.

Resistant varieties of plants

Choose resistant varieties of plants. If reseeding or establishing a lawn, use grasses containing an endophytic fungus like fescues and ryegrasses. This type of fungus keeps grubs away. Companion plants like larkspur and geranium are toxic to grubs.

Products

There are commercial grub-control products for professional pest control operators, and some domestic products for homeowners. For all three grub species, apply a treatment just after the larvae have hatched, in mid- to late-August or in mid-September, when the turf is moist.