Chafer Grubs, damage to lawns and controls

By Howard Drury

A major pest is ruining lawns over a large area of the West Midlands. The problem occurs in isolated instances over much of the British Isles, but is not a national problem yet. Symptoms begin with a small brown patch that looks as though the area has been visited by a dog that has urinated. This patch normally occurs in early summer and the area quickly becomes untidy and often a yellowing in appearance and the grass becomes easily separated from the soil with no apparent root system. Areas spread and merge throughout later summer as the larvae of this pest eat off the roots. Birds especially starlings, crows, magpies and jays along with woodpeckers may be seen scouring the soil looking for larvae to eat. Badgers and foxes may also dig extensively looking for larvae, which is a particular delicacy in their diet.

The problem is caused by the larvae of the chafer beetle. This is a member of the coleoptera or beetle family comprising of over 400,000 species in northern Europe. Up to 5 species of chafer are found in the UK. Some are found as adults on garden plants and wild vegetation while others are rarely seen. In all cases young larvae or grubs live in soil eating mainly plant roots. They have now become a major problem in the Wombourne, Norton and Stourbridge areas of the West Midlands. They nearly always attack the best maintained high quality closely mown lawns on sandy soils and always only the part of the lawn in full sun. The damage caused by predators such as birds, badgers and foxes can be as bad as that caused by the chafer grub itself.

 The larvae of all five chafer grubs are soft bodied, white and C-shaped and can be up to 40 mm long. They have a distinct, well-developed brown head and three pairs of thoracic legs. They feed on the roots of many plants in the garden including grasses and in the countryside often feed on old pasture land. Raspberries, Strawberries, Potatoes, Lettuce and many ornamentals are attacked. Symptoms are similar to that of the vine weevil. Plants wilt as though they are short of water; this is because main water transporting roots have been eaten. Most severely affected plants die shortly after being attacked.

Brown Chafers (Serica brunnea) are around 15 mm long and entirely reddish brown. They are normally only found in wooded areas and are very common but do not cause much of a problem to the gardener.

 Cockchafer (Melolontha melonotha) Sometimes called the May Bug as it is often seen swarming in large colonies on apples, oaks and other trees on warm nights at that time of the year. Adults can reach 30 mm in length and have reddish brown wing cases and white triangular markings on the side of their abdomen. Larvae can reach as much as 40 mm in length and are the largest of all chafer grubs. Although common and very large this species is not seen in huge numbers.

 Garden Chafer (Phyllopertha horticola) One of the smaller species only 12 mm in length and generally metallic blue in colour with brown wing cases. The larvae of this species are particularly a problem on turf. Most common on light soils overlying chalk or limestone. This is the number one problem here in the West Midlands.

 Rose Chafer (Cetonia aurata) Often seen on roses in June eating leaves buds and flowers. The chafers are metallic green and 20 mm long adults, while larvae are of a similar size and feed mainly on dead wood and rotting vegetation. They are not found in larger numbers, and the larvae do not constitute a problem for the gardener or his lawns.

 Summer Chafer (Amphimallon solstiitialis) This is another small species rarely exceeding 12mm in length, not a common species but occasionally seen swarming on elms or poplars. Adult summer chafers are a uniform red-brown in colour.

 Welsh Chafer (Hoplia philanthus) the numbers of this species have risen tremendously in recent years and from reported descriptions this species may also be causing a major problem on lawns. Reports from various areas of the country always mention that this species when gathering together to mate in late May or early June sounds like a swarm of bees and often congregates in Apple trees and other relatives of the family Rosaceae. There is a distinct possibility that the garden chafer and the Welsh Chafer have hybridised to produce the pest that is now ruining lawns all over the West Midlands.

Biology

 The life history of all five species is very similar, although timescale and host plants vary. Basically, female adults lay eggs near suitable host plants in early summer and larvae hatch in a few weeks. They will then feed on any underground food such as roots stems corms or tubers or on rotting wood according to species until they are ready to pupate. This timescale varies from 5 months for the smaller species to up to five years for larger species. They prepare pupal cells up to 60 cm deep in the soil to protect themselves from inclement weather and soil conditions before entering the final or pupal stage of their life cycle. Winter digging of infected areas may reveal chafer larvae, pupa or even fully developed adults ready to emerge as conditions improve. Foxes and badgers can often sense or smell the presence of these pupae and can dig huge areas of lawn up in search of food.

 Control

 This has always been difficult, but with changes to permitted uses and restrictions on active ingredients available under EU regulation 91/414 which became law on 25th July 2003 we now have even fewer control measures. Traditional cultivations still offer some of the best practical solutions. We do know that when heavy rainfall occurs in late May and June, very few eggs survive to emerge as larvae. However, it is rarely practical or morally acceptable to irrigate lawns to sufficient levels to rot the eggs. Watering affected areas after the eggs have hatched does cause grubs to migrate, reduce numbers, and in some cases actually drown them. This is an emotive and financial issue, especially during drought conditions or where water meters are fitted. There may also be legal implications in leaving a hosepipe unattended for several hours! Be warned.

Cultural Control

 Good horticultural husbandry and practice can go a long way in eradicating the pest. Regular cultivation to a good depth will bring larvae to the surface, allowing the natural predators to remove the larvae. This must be repeated several times throughout the late summer and winter while larvae are present in the soil. This is a practical solution for infected borders, but of little use in lawns. Some professional groundsmen have been practising the use of heavy rolling equipment along with professional deep spiking with expensive and heavy equipment. This may not be practical for home gardeners.

Cultural control in lawns

 Here, hand removal of grubs before the initial infection spreads is realistic using a small hand fork. Up to 200 larvae per square foot have been found and killed. Following severe infections the previous summer, it may be necessary to re-seed lawns the following spring, but not until the larvae have been completely eradicated. The use of lightweight mowing and turf cultivation equipment may also be to blame. It was always thought that the use of heavy rollers and mowers deters the laying of eggs and increases the mortality rate among young chafer grubs. Try rolling your lawn in late spring or early summer. Do not roll when the ground is dry or when waterlogged. Another old trick was to cover infected areas of the lawn with hessian grass mats or sacks that were kept moist, usually in August or September when there are dewy mornings. This was thought to attract larvae to the surface of the hessian, which is then turned over in the early morning, allowing natural predators an early and substantial breakfast! Today, polythene may be substituted. There are rumours that diluted Coleman’s Mustard applied in water may have the same effect on the Chafer larvae as it does on worms, causing them to come to the surface where they can be collected and disposed of safely. More information is available from The Sports Turf Research Institute, who are based at Bingley in Yorkshire. A most important angle appears to suggest that watering your lawn around egg laying time through until August and leaving the grass somewhat longer from April until early July (50 mm) will deter egg laying or cause eggs to rot.

Chemical Control

In past years various chemicals were available to home gardeners, today these have disappeared.

Biological control is available today but it cannot be purchased directly from garden centres, they merely forward your order to a laboratory that will supply literally many thousands of tiny nematodes smaller in length than the diameter of a human hair. Two species are commonly used called Heterorbditis species or Steinernema carpocapsae these tiny predators are supplied direct from the laboratory to your door for immediate application. One such company supplying the first nematode is Just Green offer a pack of 50 million nematodes which will treat 100 sq metres for £40. The only limitations to this product seem to be the recommendations that it is applied to moist but not soaking wet ground during July, August and September while the soil temperature is above 12C or 57F. It is also said to work better on sandy soils. If there is no food such as chafer grubs for nematodes, then the predator will die, making further applications necessary if the pest appears again. (Just Green offers an on-line ordering facility at http://www.just-green.com/232/Just-Green-Just-Chafer-Grub-Killer-.html). Nematodes cannot be used where chemical treatments have been used in recent years, with even the slightest trace of pesticides being sufficient to kill the tiny nematodes.

Leatherjackets (European Crane Fly)

Leather Jacket larvae in lawns

Leatherjackets are the larvae of the European Crane Fly or Daddy Long Legs as they are commonly known. The larvae cause damage to lawns by feeding on the roots of grass plants. The symptoms and damage to the lawn is similar to Chafer Grub damage  hence the information is included her.

Adult crane flies hatch from pupae in late July and August and lay their eggs in the ground within 24 hours of hatching. The larvae hatch about 2 weeks later and start to feed on grassroots, which continues through winter and into spring. They stop feeding in May/June, when they will pupate in the soil. In general, they stay underground in the day and move up to the turf leaves at night. They are very sensitive to drying and do not survive if they are dried out by the sun. On very cloudy days when the turf is wet, you can see the larvae in the turf. They are about 25 mm long and have a grey/brown leathery skin.

Damage to lawns occurs from autumn to spring, but is most severe in the spring, when the leatherjackets are fully grown. Symptoms may appear as yellowing, weak areas of grass where the roots have been damaged. The grass can be easily pulled up with little or no root growth. Damage is usually more severe when the previous autumn has been mild and wet. Secondary damage can also be caused by birds and mammals digging up turf in their search for leatherjackets.

The time to control the insects is when they are in the larval stage, not flies. They can be controlled by removing by hand or applying a biological nematode, which attack the larvae, killing them within a few weeks. They are specific to the pest concerned, therefore safe for the user, children, pets, wildlife and the environment. The main season for application is late August until the end of October. A spring application can be made in the case of severe infestations if the soil temperature is over 10 degrees Celsius.

Howard Drury, Horticultural Broadcaster, Speaker, Lecturer, Writer, Adviser and Consultant

Morningside, 8, Bagnell Road Kings Heath Birmingham B13 0SJ

Telephone 0121-443-3212 Fax 0121 441 2760 Mobile 07710-038-467

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The information given in this Fact Sheet is provided in good faith.  It is however of necessity general information and advice on the topic.  Howard Drury will not be under any liability in respect of the provision of such advice and information, and you are strongly advised to seek independent advice on any particular gardening problems or queries you may have, preferably from experts who can (when appropriate) inspect the problem before providing advice.

© 2022. This material has been produced by Howard Drury and must not be reproduced in part or full without the written consent of Howard Drury, Kings Heath, Birmingham, B13 0SJ.

JHD/03/02/2022