Worm casts on lawns

Worm activity is most evident on lawns but can also be a nuisance in gravel paths.

Symptoms

Deposits of mud (worm casts) are found on the surface of lawns, and are particularly noticeable if the turf is of fine quality. The casts become smeared by lawnmowers and feet, making the turf muddy and slippery. Moss and weeds can develop on these muddy spots.

Worm casts are produced mainly during September to October and March to early May when the soil is warm and moist, and also in spells of mild weather during the winter. Worms remain close to the surface under these conditions. When the soil is dry or cold they go deeper into the soil, resulting in less deposition of worm casts on the surface.

Cause

Allolobophora species of earthworms are responsible. These worms feed on decaying vegetation in the soil and they deposit their muddy excrement on the lawn surface. Earthworms can have beneficial effects in lawns as their burrowing activities help in aerating and draining the soil. They also incorporate organic matter into the soil by pulling dead leaves into their tunnels.

Control

Disperse worm casts when they are dry, with a besom broom or an up-turned wire rake moved from side to side. However, there are often few days during the autumn to spring period when worm casts are sufficiently dry for this to be an effective solution.

The regular addition of spring/summer lawn fertilisers based on ammonium sulphate may make the topsoil acidic enough to discourage earthworms.

Pesticides for the control of lawn pests are no longer available to home gardeners. Pesticides marketed for professional use cannot be used on garden lawns, although it is possible have them applied to sports turf, such as a bowling green. In that type of situation it may be worth employing a contractor who has the necessary Certificate of Competence to use professional pesticides on amenity turf.

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