Chafer grubs in garden borders
The large white c-shaped grubs of chafer beetles are sometimes found in gardens. Most do not cause problems, some feed on decomposing vegetable matter and help nutrient cycling. A few species can damage roots including some that feed on turf (see chafer grubs in lawns).
Plants affected Many do not damage plants
Main symptoms Large white c shaped grubs with three pairs of legs and a brown head
Caused by Larvae of a chafer beetles
Timing All year
What are chafer grubs?
- Chafer grubs are the larvae of chafer beetles. There are nearly 20 species of chafer in Britain, most do not cause problems in gardens and some species are very rare
- 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 in accumulations of rotting vegetable matter. Adult maybugs are over 3cm in length and active during May, often attracted to light, more information on this insect is available from the Wildlife Trusts
- The grubs of chafers (known as scarabiform) are all c-shaped, with a brown head and three pairs of legs. They are similar in appearance to stag beetle, Lucanus cervus (read more from Peoples Trust for Endangered Species) 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. If stag beetle larvae are exposed when digging around dead tree roots they should be recovered so that they can complete the life cycle. Dung beetles feed on animal dung and are without them dung would soon pile up.
- One species of chafer grub is often found in compost heaps, areas rich in rotting vegetable matter and occasionally organic matter rich potting composts. This is the rose chafer (Cetonia aurata). The adult beetles are about 2 cm long and metallic green. The adults can feed on flowers and leaves but this insect may be considered beneficial as it helps the composting process as a grub
- A few species of chafer 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 of plants
- Garden problems are 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
Chafer grubs found in compost heaps and organic rich soil are often Rose Chafer larvae which do not normally damage plants and are part of the composting process.
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.
Most species of chafer grub do not need control, and species such as the rose chafer are beneficial. Other than in lawns, chafer grubs are rarely cause damage to garden plants. Adult chafer beetles
Non-pesticide controlTolerate the presence of chafer grubs in garden borders, in some cases they are beneficial and they are easily confused with stag beetle larvae, which feeds on dead tree roots.
Remove larvae of problem 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.
You can buy pathogenic nematodes, usually Heterorhabditis bacteriophora, which enter the larvae and infect them with a fatal bacterial disease. These microscopic animals can be watered into the lawn or garden border when the ground is moist and soil temperature range between 12-20ºC (55-68ºF). This biological control is available from some biological control suppliers and some garden centres. The ground around the edge of affected areas should be targeted to deal with larvae spreading out from “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.
There are currently no pesticides available to home gardeners for the treatment of insects in the soil
Biological control suppliers (pdf document)
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