Chafer grubs in garden borders

The large white c-shaped grubs of some chafer beetles can damage the roots of plants. Some species cause serious damage to lawns (for these see chafer grubs in lawns). Most chafer grubs are not pests, these include some that feed on decomposing vegetable matter and can be useful composters.

Rose chafer beetle on hogweed flower

Quick facts

Common name Chafer grubs (various species)
Plants affected Various
Main symptoms Roots are eaten by large white larvae
Caused by Larvae of a chafer beetles
Timing All year
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What are chafer grubs?

  • Chafer grubs are the larvae of chafer beetles. There are nearly 20 species of chafer in the UK and most do not cause problems in gardens
  • The larvae have white bodies, brown heads and three pairs of legs the largest species, the cockchafer or Maybug (Melolontha melolontha) can reach 50mm in length. All chafer grubs feed in the soil or accumulations of rotting vegetable matter
  • The grubs are similar in appearance to stag beetle (Lucanus cervus) and dung beetle larvae. The former is usually only found associated with dead tree roots and can reach 11cm in length and the latter dung, neither are problems in gardens. If stag beetle larvae are exposed when digging around dead tree roots they should be recovered so that they can complete the life cycle
  • A few species can be occasional problems in garden borders, feeding on plant roots; these include the cockchafer and summer chafers (Amphimallon solstitiale). These have larvae that can feed in the soil for up to three years and occasionally damage the roots a variety of plants
  • The biggest garden problems are usually caused by the smaller garden and Welsh chafers (Phyllopertha horticola and Hoplia philanthus) (up to 20mm) whose grubs are mainly found under turf where they can destroy the root system. Animals such as foxes badgers and corvid birds often dig for these grubs in infested turf
  • One species of chafer grub is often found in compost heaps or areas rich in rotting vegetable matter. This is the rose chafer (Cetonia aurata). The adult beetles are about 2 cm long and metallic green. The adults can cause minor foliar damage to plants but this insect may be considered beneficial as it helps the composting process as a grub

Symptoms

Where problem chafer species are present plants lack vigour and examination of plant roots will often show signs of being eaten. Large c-shaped grubs can also be found.

Damage to lawns can be more extensive, for more information see chafer grubs in lawns.

Control

Non chemical

Remove larvae of pest species from soil as they are found. Cultivation of the ground can briefly expose the grubs to predators, such as birds, and make the ground less attractive as egg-laying areas. 


Biological control

You can buy pathogenic nematodes, usually Heterorhabditis bacteriophora, 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 biological control is available by mail order from some biological control suppliers or some garden centres. The ground around the edge of affected areas should be targeted to deal with larvae spreading out from infestation “hot spots”. The nematodes should be applied as soon as possible after purchase, following the suppliers’ instructions. It may be necessary to water the soil before and after application to ensure the soil is sufficiently moist for nematode activity and survival

Chemical

There are currently no pesticides available to home gardeners or the treatment of soil pests.

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