History
In parts of Ontario, there are three species of white grubs that infect lawns: European chafer, June beetle, and Japanese beetle. The most common species is the European chafer, which has come from Europe and has invaded much of the southern portion of the province. It occurs along Lake Erie and has spread to areas north of London and Kitchener and east of Toronto. Another species, also imported, is the Japanese beetle and it has become established in the Niagara Peninsula and Hamilton–Wentworth region. Grubs of both species cause considerable damage to turf-grass, while the Japanese beetle adult is a serious pest of a large number of fruit and ornamental trees and shrubs. June beetles are native to North America, with approximately 152 species occurring in the United States and Canada. In Ontario there are three principal species.
Description
Grubs of all species have soft, white, C-shaped bodies with tan or brown heads and six prominent, spiny legs. They are quite small when first hatched (3 to 4 mm long), but at maturity reach a length ranging from 2 cm (3/4 inches) for a Japanese beetle larvae to 4 cm for the June beetle grub. A healthy grub is milky white in colour, with the dark contents of its gut showing prominently through the cuticle at the hind end of the abdomen.
Typical white grub.
Identification
A distinguishing feature among the three species is the pattern of spines occurring on the underside of the tip of the abdomen. On either side of the midline, at the tip, a line of stout spines occurs. In the June beetle grub these two lines are parallel, converging at both ends. In the European chafer grub, the lines of spines are parallel until the tip where they diverge. In the Japanese beetle larvae the spines form a V-shaped pattern.
June Beetle Grub.
Japanese Beetle Grub spines.
European Chafer spines.
Monitoring
Because grubs feed on turf roots, homeowners are often unaware that they have grubs until they suffer significant turf loss or until secondary pests tear up their lawns. The key to success with grubs is knowing that you have them before you see turf damage. To do this, you must monitor the soil / thatch interface in the early part of August. At that time the grubs will be big enough that they are clearly visible, but they will be small enough that they have not caused significant damage. A good method for detecting grubs is to cut three sides of a square of turf roughly 0.3 m long (12 inches) with a sharp knife and pull the turf back. Count the number of grubs and this will give you the number per 0.1 meter squared (1 sq. foot). If the number of grubs exceeds the threshold (number of grubs which the turf can tolerate without excessive damage occurring), then a control action is warranted.
Method for detecting grubs. Determining grub density by opening up a patch of turf.
Damage
The grubs of all species feed on the roots of many plants, but prefer the fibrous roots of turf-grasses. As the root system is destroyed, sections of turf wilt, turn brown and can be easily pulled back to reveal grubs beneath. Skunks and birds searching for grubs as food cause secondary damage. Damage is most severe in the fall and the spring when the grubs are increasing in size rapidly and feeding near the surface.
Cultural Control of Grubs
Summer and fall weather conditions can have an effect on turf health and vigour which indirectly affects grub damage. Low rainfall during July and August can cause egg mortality because the eggs need to absorb moisture from the soil to hatch into grubs. In general, when there is sufficient rainfall or when turf is irrigated regularly, grub damage is reduced. Healthy, actively growing turf will have more roots and, hence, can withstand more grub feeding without turf loss. Conversely, lawns which are not vigorous and healthy will show turf damage quickly after small amounts of grub feeding. Maintaining a healthy lawn is your first line of defense against grubs.
Biological Control
Beneficial nematodes, neem oil, and milky spores have been used to gain control. The application of these products is key in their ability to provide effective control. The applicator should follow the manufactures specifications exactly.
