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.
What are chafer grubs?
Chafer grubs are soil-dwelling larvae of various chafer beetles. They feed on plant roots, especially those of grasses.
Chafer grubs 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 (eg 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 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
- Repair damaged turf by re-sowing with grass seed or laying turf in April
- 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 during the summer to early autumn 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
- A pesticide - Bayer Provado Lawn Grub Killer - is available to home gardeners for controlling chafer grubs in lawns. The product contains imidacloprid*
- The best time for treatment is in late May to early July, when the more vulnerable young larvae are present
* Please note this product has been withdrawn. The withdrawal (in effect a ban) came into force on 30 September 2013, but there was a period of grace to use up these materials by 30 November 2013. It is now illegal to use them, any remaining products should be taken to a manned local authority household waste site where they should be handed over to the staff. For information on waste disposal sites see www.pesticidedisposal.org. It remains legal to use other neonicotinoid-based products that are not affected by the withdrawal. This withdrawal follows concern over their effects on bees.
Pesticides for gardeners (Adobe Acrobat pdf document outlining pesticides available to gardeners)
The 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
- 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
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