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
Tolerate 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 or the treatment of insects in the soil
Biological control suppliers (pdf document)