Advice
RHS Help & Advice
Chafer grubs in lawns
The species most often found in lawns are the garden chafer, Phyllopertha horticola, and the welsh chafer, Hoplia philanthus; the latter is particularly found in sandy soils.
Adults of P. horticola are about 9mm long and have a metallic green head and thorax with light brown wing cases. H. philanthus is a similar size with a black head and thorax and reddish brown wing cases.
The larvae have stout white bodies curved in a letter C shape, light brown heads, with three pairs of legs at the head end. They are bigger than the adults and if straightened out would be up to 18mm long. Other less troublesome species of chafer grubs can also occur in turf and these can have larvae up to 30mm.
Symptoms
The larvae eat the roots of grasses and other plants. Damage to lawns tends to be most obvious between autumn and spring when the grubs are reaching maturity. Patches of the lawn may become yellowish. Birds, particularly of the crow family, such as jays, magpies, rooks and crows, and badgers and foxes feed on the grubs, tearing up the lawn in the process (see picture right). Infestations can be highly localised and sporadic in occurrence.
Adults feed on the foliage of various plants but generally cause little damage.
Biology
In heavily infested gardens the adult beetles fly up from turf in large numbers at dusk from late May to June. Eggs are laid in the turf and these hatch a few weeks later. The grubs feed on roots but do not start to cause significant damage until early autumn, by which time the larvae are becoming fully grown. They overwinter as larvae and pupate in the soil in the spring.
Control
Repair damaged turf by resowing with grass seed or laying turf in April. Poorly maintained lawns are more susceptible to damage, so attention to feeding, watering and moss prevention will help to avoid damaging infestations.
A pesticide is available to home gardeners for controlling chafer grubs in lawns. This is Provado Lawn Grub Killer, which contains imidacloprid. The best time for treatment is in June to July, when young larvae will be present.
A pathogenic nematode, Heterorhabditis megidis, which attacks the larvae by infecting them with a fatal bacterial disease, can be watered into the soil during the summer to early autumn when the ground is moist and in the temperature range 12-20oC (55-68oC). This microscopic nematode is available by mail order from some biological control suppliers.