What are they?
White grubs are the larvae of certain beetles, like June beetles and chafers. Grubs are one of the hardest lawn pests to deal with.
Grubs are white or yellowish and have fleshy, wrinkled, C-shaped bodies with tan or brown heads and six spiny legs. They are quite small when they hatch, but when fully grown are from 2 to 4 cm (.75 to 1.5 inches), depending on the species.
The most common white grubs infesting turf in Canada are those of the native June beetle or June bug. Two smaller exotic species, the European chafer and the Japanese beetle, have been accidentally introduced into Canada and are found mainly in the Niagara peninsula. The European chafer, though, has recently migrated further north and east, and is responsible for much of the lawn damage in recent years in eastern Ontario.
June beetle adults are shiny reddish brown, and up to 2.5 cm (1 inch) long. The adult European chafer is light brown or tan, and is about 1.3 cm (0.5 inches) long. The adult Japanese beetle is metallic green and bronze, and about 1 cm (less than 0.5 inches) long.
Should I be concerned?
It takes the June beetle three years to mature, while the European chafer and the Japanese beetle take only a year. On their way to maturity, there are times when they are most active and most damaging to a lawn. Typically, outbreaks of white grubs happen every third year.
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.
White grubs do the most damage at these times:
June beetle grub:
- Year 1 - August through September
- Year 2 - April through September
- Year 3 - April through May
European chafer grub:
- Year 1 - March through April
- Year 2 - September through November
Japanese beetle grub:
- Year 1 - April through June
- Year 2 - September through October
How can I get rid of grubs?
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.
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.
Some provinces and municipalities have placed more restrictions on the use of certain approved lawn and garden pesticides. Please check with your city, province, or local lawn care centre for more information.
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.
If you use a pesticide to control your pest problem, read the label to make sure you are choosing the right product for the right pest. Follow all label directions and warnings carefully. Always look for a Pest Control Products (PCP) number on the label so you know the product has been approved by Health Canada. See Use pesticides safely for more information on using pesticides safely.
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.
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