Chafer grubs in lawns

A combination of chafer grubs and the larger animals that feed on them can quickly turn a neat lawn into something that resembles a ploughed field.

Chafer grubs. Credit: RHS/Science.

Quick facts

Common name Chafer grubs, mainly garden chafer and welsh chafer (not confined to Wales!)
Scientific name Phyllopertha horticola and Hoplia philanthus
Plants affected Lawns
Main symptoms Scruffy turf with pieces pulled up by birds and animals searching for the grubs
Most active Grubs September–April; adult beetles May–June

What are chafer grubs?

Chafer grubs are soil-dwelling larvae of chafer beetles. Depending on the species of chafer they either feed on decaying plant material or plant roots. Several species that feed on the roots of grasses can become a pest problem in lawns

Symptoms

Some species of chafer grub eat the roots of grasses and other plants. Evidence of their activities can be seen in a number of ways:

  • Damage to lawns is 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 (e.g. jays, magpies, rooks and crows), and badgers and foxes feed on the grubs, tearing up the loosened turf in the process
  • Damaging infestations can be highly localised and sporadic in occurrence
  • Chafer grubs can be found in the soil under the loose turf. They have stout white bodies curved in a C shape, light brown heads, with three pairs of legs at the head end. They are bigger than the adult beetles and, if straightened out, would be up to 18mm (almost 3/4in) long
  • Other less troublesome species of chafer grubs can also occur in turf and garden borders these can have larvae up to 30mm (over an inch)
  • Similar root damage in lawns can also be caused by leatherjackets but churning up of the turf by other animals is less likely where leatherjackets are the problem

Control

Non-chemical control

  • Repair damaged turf by re-sowing with grass seed or laying turf in April when the chafer grubs have moved deeper into the soil to pupate.
  • Poorly maintained lawns are more susceptible to damage, so attention paid to feeding, watering and moss prevention will help avoid damaging infestations
  • You can buy pathogenic nematodes, Heterorhabditis megidis, which attack the larvae by infecting them with a fatal bacterial disease. These microscopic animals can be watered into the lawn when the ground is moist and soil temperature range between 12-20ºC (55-68ºF). This biocontrol is available by mail order from some biological control suppliers or some garden centres. The turf around the edge of affected areas should be targeted to deal with larvae spreading out from infestation “hot spots” in the lawn.  However, by the time areas of infestation become apparent, the soil may be too cold for nematodes to be effective.  As a preventive measure, apply nematodes in July to September against chafer grubs. Nematodes should be applied as soon as possible after purchase, following the suppliers’ instructions for use.  It may be necessary to water the lawn before and after application to ensure the soil is sufficiently moist for nematode activity and survival.

Chemical control

There are currently no chemical controls for chafer grubs on lawns.

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Biological control suppliers (Adobe Acrobat pdf)

Biology

The chafer species most often found damaging lawns are the garden chafer, Phyllopertha horticola, and the welsh chafer, Hoplia philanthus; the latter is particularly found in sandy soils and is not confined to Wales.

  • Adults of P. horticola are about 9mm (3/8in) long and have a metallic green head and thorax with light brown wing cases
  • Hoplia philanthus is a similar size with a black head and thorax and reddish brown wing cases
  • 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
  • Two other species, which are generally less damaging, are the summer chafer (Amphimallon solstitialis) and the brown chafer (Serica brunnea).  The latter is generally found in or near wooded areas on sandy soils and is about 9mm long and reddish brown in colour.  The summer chafer is light brown, about 16mm long, and distinctly hairy.
  • The adult beetles feed on the foliage of many plants but are generally not a problem.  They will, however, sometimes damage the flowers of roses and other plants
  • The grubs feed on roots but do not 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

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