Summer chafer: detection, prevention & treatment

Summer chafers can be a bit of a nuisance and their larvae can cause extensive damage to the root systems of plants. Find out how to combat summer chafers here.

The summer chafer (Amphimallon solstitiale), also known as the European June beetle, has become more and more of a problem in recent years. In some regions, this beetle has become a real plague. Read on to find out how to recognise, prevent and combat European June beetles.

Identifying summer chafer beetles and larvae

Summer chafer grubs (the larvae) can cause extensive damage to lawns by feeding on the grass roots. As a result of this, the lawn may get patchy and could eventually dry out completely. If you notice areas of dry grass in your lawn that are easy to pull up, this could be an indication of a summer chafer larvae infestation. In this case, it is important to find the source of the problem quickly by looking at the soil under the damaged lawn. If you find thick, white, C-shaped larvae in the soil, these may be summer chafer grubs. Summer chafer grubs have three pairs of legs along the sternum and a brown head, as seen in the picture below. Summer chafer larvae are up to three centimetres in size and are easy to confuse with garden chafer and cockchafer grubs. In practice, however, it is not necessary to distinguish between the grubs, as those of all three beetles are pests that you will need to control if you find large numbers of them in your garden. While these grubs usually only cause visible damage to lawns, they can also damage the roots of other plants.

Summer chafers are brown beetles with yellow-brown hair that covers their body. They can reach between 14 and 18 mm in size, making them about half the size of a cockchafer, which can reach up to 30 mm in length. These unpleasant beetles are capable of flying and mainly visit fruit trees and other deciduous trees and feed on their leaves. Generally speaking, however, adult summer chafers will not cause too much of a problem. Due to these beetles’ limited lifespan, infested plants typically recover quite quickly.

Summer chafer beetle overview

Summer chafer beetles only appear from the first day of summer (21^st June) until mid-July at the latest. As dusk falls, the male beetles fly up and about, seeking females to mate with. The bothersome beetles can appear in large numbers and can thus be quite irritating during the summer nights. The females, which are fertilised after the flight period, lay their eggs in small batches in the ground. In total, a female summer chafer will lay about 40 eggs during her lifetime. The first grubs hatch from the eggs after three weeks. However, it takes some time before they become full-grown larvae. In areas with warmer ground temperatures, the grubs only need two years to pupate. In cooler areas, on the other hand, larval development takes three years. During this period, the grubs feed on plant roots, wreaking havoc on lawns and the like.

Female summer chafers prefer to lay their eggs in sandy and light soils, as the larvae cope better with dry soil. This is why European June beetles tend to avoid damp and wet areas.

Now, before we delve into prevention and treatment, we would like to point out that summer chafers pose absolutely no danger to humans. As disturbing as it may be for one to land on you, they cannot bite or sting you. Hence, there is no need to get rid of summer chafers unless they are causing damage in your garden.

Summer chafer prevention

There are several ways to keep summer chafer infestations at bay. Since the beetle itself does not usually cause long-term problems, you should concentrate your efforts on the grubs. Lawns are often used as breeding grounds for June beetles, so they must be made unattractive to females looking to lay their eggs. The most effective way to protect your sensitive lawn roots from the hungry larvae is to prevent summer chafers from laying their eggs there in the first place. For continued protection, maintain your lawn by fertilising and mowing it on a regular basis. Dense and lush lawn growth makes laying eggs troublesome for summer chafers. When mowing the lawn, do not cut it too short, as it is easier for summer chafers and other beetles to work their way through short lawn grasses to penetrate the soil and lay their eggs.

Installing landscape fabrics at a low soil depth has become common practice in those areas that are seriously affected by summer chafers. Although such fabrics can be costly, summer chafers are unable to penetrate them and lay their eggs in the soil, making grubs and molehills a thing of the past.

Summer chafer management

In addition to preventive measures, you can also tackle the pests directly. However, combatting the adult beetles barely makes a dent in infestations. And, although you can buy garden beetle traps, they are not suitable for catching summer chafers. So, you are better off focusing your efforts on the larvae.

When fighting summer chafer grubs, do not reach for plant protection products. The use of pesticides in soil is generally problematic, as beneficial microorganisms are highly sensitive to even the smallest amounts of pesticides. We highly recommend the alternative practice of using predatory nematodes. The nematodes secrete bacteria which decompose the chafer grubs. The grubs are then pre-digested by the bacteria and are subsequently consumed by the nematodes. These beneficial insects, which are harmless to humans and pets, are known as Heterorhabditis bacteriophora or HB nematodes. Nematodes are easy to use – you simply add them to water and pour the solution over the area requiring treatment. Once the nematode solution has been applied to the area to be treated, the beneficial insects will begin to tackle the destructive summer chafer grubs.

Tip: HB nematodes are also effective combatants against cockchafer and garden chafer grubs.

How to use HB nematodes as beneficial insects:

• Use against suffer chafers between July and September.
• Ensure ground is at least 12 °C.
• Keep soil moist (not wet!) for the duration of treatment.
• Only apply nematodes in the morning or evening, as they are very sensitive to light.
• If you are dealing with a particularly heavy infestation, you may need to repeat the nematode treatment.

See our in-depth article to find out everything you need to know and further application possibilities for nematodes as beneficial insects.

An alternative method of combatting summer chafers is tilling the soil to a tilling depth of 10 cm. This should destroy most of the summer chafer grubs and may prevent the need for further control measures. Of course, you should only use this control strategy in an emergency because tilling not only kills the grubs, but it also destroys plants and can have a negative impact on the soil quality as well.

Grubs can cause massive damage to your lawn, so it is best to tackle them early on before they become a problem. See our article on combatting grubs in the lawn for some top tips.