Pest and Diseases - Leatherjackets

Signs - affected plants may turn yellow, wither and die. Small plants and seedlings may be severed at ground level. The grey - brown leatherjackets are up to 3.5cm (1 1/2inches) long, smooth, tubular and legless, rarely seen above ground, usually found just below the surface particularly in grass where a small population that causes no visible damage is more common than not.

Damage - feed on roots particularly affecting young annuals, bulbs and vegetables, predominantly affects land that has been recently brought into cultivation recently and usually subsides after a couple of years. The leatherjackets are the larvae of crane flies, daddy-long-legs.

On lawns, more damage is usually done by birds and small mammals digging the leatherjackets up than by the leatherjackets themselves.

Treatment - the traditional way to bring them to the surface is by soaking an area of lawn with water and then covering with black plastic sheeting (weighted down) or sacking. Leave for a day then lift the cover and remove the leatherjackets. Put them on a bird table - the birds love them. Whenever I've been lifting turf to establish a plant border or bed, leatherjackets are invariably uncovered. I've always had a companion blackbird or robin who will sit to one side, then when I walk away briefly from the bit I've just uncovered will dart down pick up a grub and re-position itself for the next swoop. Sometimes, if they're a bit braver and closer, you can pick a grub up and throw it to the bird.

Biological control

The biological control for leatherjackets is the predatory nematode Steinernema feltiae. It will not control all leatherjackets but can reduce numbers which in turn will reduce the damage to grassland and turf.

Apply between March and June when soil temperature should be + 12 °C, later in heavy soils, earlier in light soils.