Leatherjackets and chafer grubs

Both chafer grubs (the larvae of chafer beetles) and leatherjackets (the larvae of crane flies, or daddy-long-legs) live in the soil. They eat the roots of grasses and, as a result, cause problems in lawns.

Leatherjackets

Leatherjackets have tubular, greyish-brown or darker bodies, up to 3cm (1¼in) long, with no legs or an obvious head. They may be confused with cutworms [LINK to Caterpillars], the caterpillars of several moth species.

Adult crane flies mainly emerge and lay their eggs in the turf or soil surface from August to October. When the eggs hatch in a few weeks, the young leatherjackets start eating plant roots. During mild winters, they continue to feed and can cause lawn problems by late winter. During cold winters, they overwinter as small larvae and don’t cause significant damage until the following summer. When fully grown, the leatherjackets pupate in the soil, eventually emerging as new adults crane flies.

Leatherjackets and leatherjacket damage are usually worse in a wet autumn.

Chafer grubs

Chafer grubs are large, creamy-white, C-shaped grubs with large brown heads and six legs. They can be confused with vine weevil larvae, but these are much smaller and legless.

The most damaging chafer species are the garden chafer, Phyllopertha horticola, and the welsh chafer, Hoplia philanthus – which isn’t just confined to Wales. Adult garden chafer beetles are around 9-10mm (3/8in) long, with a metallic green head and body with light brown wing cases. Adult welsh chafer beetles are the same size with a black head and body and reddish-brown wing cases.

In late spring/early summer, usually at dusk, the adult beetles fly up from the lawn in large numbers to mate. Females lay eggs in the turf and these hatch into the larvae (grubs), which start to feed on the grass roots. At first, they do little significant damage, until autumn, as they become fully grown. They overwinter in the soil as larvae and pupate in the soil in spring.

• Lawn grasses
• Other grasses
• Small border and vegetable plants

Both chafer grubs and leatherjackets are mainly pests of lawns. They eat the roots of lawn grasses and, as a result, cause yellowing and death of the grass and so problems with the lawn. Leatherjackets will also eat the roots of small and young plants, both ornamental and vegetables, killing them.

Further damage is caused by birds (especially rooks, crows and magpies who peck holes in the turf), but especially badgers and foxes who can turn the lawn into something looking like a ploughed field to search for the grubs.

The adult chafer beetles feed on the leaves of many plants, but don’t pose a problem.

Once leatherjackets and chafer grubs are established in the lawn, it is very difficult to fully control them that year. So keep a close eye on the health of the grass – or signs of birds pecking – and take early action to deal with them.

Biological controls, based on nematodes. For chafer grubs, apply the biological control from July to September. For leatherjackets, apply from August to early October.

As many birds, especially rooks, crows and magpies, actively search for and eat both larvae, give them a helping hand and, at the same time, prevent them damaging the lawn by pecking deep holes to get at them. Water the lawn in the evening and cover with sheets of black polythene, carpet or similar to exclude the light; this will help draw the larvae to the soil surface. Then take away the coverings early in the morning (ideally at dawn!), so the birds can deal with them.

Unfortunately, there are currently no insecticides approved for home gardeners to use to control leatherjackets or chafer grubs.

It is more-or-less impossible to stop crane flies and adult chafers laying eggs in your lawn, and so prevent any possible problems. But keeping the lawn growing strongly may help prevent/reduce problems.

• Lawn fertilisers
• Grass seeds
• Lawn scarifiers