Tuesday 17 September 2019

Gerry Daly: How to reduce the slug population in your garden

There's an entire universe in the soil, writes Gerry Daly, and it can be harnessed to control your pests

Slugs cause a lot of damage, especially to vegetables or to seedlings
Slugs cause a lot of damage, especially to vegetables or to seedlings

Gerry Daly

The ordinary soil of gardens is full of life. It's like a universe within the universe, full of all sorts of creatures, fungi, bacteria, earthworms, viruses, beetles, smaller insects, ants, slugs, wood lice and many other kinds. It is in constant, unseen tumult as these animals feed, live and breed for the future. Some of these creatures are eating plants, the roots of plants, the stems and leaves, and some are eating other insects and creatures themselves. They are parasites and predators of various kinds.

And there are diseases such as bacteria, fungi and viruses that attack living creatures within the soil and kill them, or at least make them very ill and less harmful. In recent years there has been a lot of interest in these interactions in the soil, which can then perhaps be used as a defence against pest species. So for example, the use of eelworm to control vine weaver larvae and slugs and cockchafer grubs in recent years has become quite common.


Nematode worm is the correct name for them, called eelworm, because they look like an eel, curving and very narrow and thin. They're actually microscopic. Some of the very large ones might be just about visible with excellent vision, but most of them are microscopic and cannot be seen at all. There are some of them that are parasitic on plants, such as potato cyst eelworm. There are others that are parasitic on slugs and others are parasitic on vine weevil larvae and can be used for their control. So these controls have been developed on a commercial basis and are available to buy in garden centres. But the wild eelworms also exist in most soils.

If you use just peat, you will get no natural parasite activity by eelworm. The same is true of slugs. The peat lacks these defences, friendly creatures if you like, that protect plants against true pest species. If you use ordinary good garden soil, you're introducing wild eelworm into the compost mix. So if you use half and half, ordinary garden soil, not sterilised, and half compost, which supports these creatures, they will give a good defence against vine weevil larvae. You may still have some larvae, but the level of damage will be less severe.

The commercial product comes as a powder in a packet and is mixed with water for distribution purposes. In the case of slugs, the eelworms are not killing slugs themselves, but are carrying bacteria which are pathogenic on slugs. Eeelworms are vectors or carriers of a disease that affects these pest species.

Vine weevil eelworm really only work when the soil temperature is about 12 degrees Celsius, which means early and late summer, in particular, when the little C-shaped white grubs hatch from eggs. The eelworms remedy works, but may need a second application.

Slugs cause a lot of damage, especially to vegetables or to seedlings. You can use slugs against themselves, so to speak. Sickly or recently dead slugs, not poisoned, may have a larger-than-usual opening at the side of their head. Gather some of these and use them to infect healthy slugs, by placing them together on a saucer in a bucket of water, so that if they leave the saucer they drown.

By mixing healthy slugs with infected ones, you create conditions that may infect them with disease. Admittedly, this can be a bit hit-and-miss. It's not anything like as certain as the prepared commercial eelworms, but it doesn't cost anything, except for time gathering slugs to make this potentially lethal concoction, and also reduces your slug population.

Take, roughly, a cupful of dead-slug water, diluted in a watering can, and then water it onto cabbage or lettuce, or whatever vegetable the slugs like to attack. By the time those vegetables are consumed, the eelworms have long passed on and there are no residues.

Bring and buy

Next Saturday, April 27, heralds the Royal Horticultural Society of Ireland's Spring Plant Sale at St Brigid's Parish Centre, Stillorgan, Dublin, 10.30am to 1pm. Plant donations accepted from 9am. Lots of good plants and always some rare plants from private collections.

In its prime

At 50, my wisteria has a massive show of violet-blue flowers ready to pop. What wonderful joy this plant has brought to hundreds, maybe thousands, of passers-by, friends and extended family. Chinese in origin, this plant revelled in the hot summer last year, a summer more akin to the heat of its homeland, and will produce probably its high point show to date. And it is just mature, by no means elderly in the lifespan of wisteria.

Summer stays

Art lovers can enjoy a brilliant garden display from June 15 to 30 at Culloden Estate, Belfast, when sculptures and installations by Dali, Damien Hirst, Grayson Perry, Julian Opie and Orla de Bri take up residence. Art tour and tea, £50pp; overnight stays also available; hastingshotels.com

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