Shoring up defences against attacking slugs


Another Life/Michael Viney: The rain's return drew a welcome incense from the soil, a rich brew of microbial gases displaced from its burrows and caverns by the sudden rush of raindrops.

I like to think my pleasure in this pheromonal cocktail is an intuition lingering from more pagan days, a guarantee of greenery and growth.

The rain also laid the dust for the silvery meanderings of slugs. Where were they all winter? Back in April, I rolled back a big sheet of black plastic fabric - a winter weed defence - and found them clustered there in dozens.

The big black ones, like half a sticky prune, called Arion ater, can stretch to 15 cm and will rock from side to side when annoyed, or so malacologists tell me. Scattered around them were the little grey field-slugs, like slippery blobs of chewing gum, Deroceras reticulatum. Both were dutifully flipped into a bucket of salty water, with apologies to their molluscan souls.

There is a certain wanton futility, and thus an extra guilt, to such slaughter of slugs on a leafy rural acre where hundreds of thousands more are waiting to take their place. Even this clean sweep did nothing about the Milax clan - the so called "keeled" slugs, with a ridge down their backs - waiting, under the soil, to bore holes in my potatoes.

Given the ability of one big black slug to mow down a whole block of seedlings in a night, the defences of any serious garden food-grower become local and intense. Before the rains came, I was out at the newly-emerged peas, heaping ramparts of sawdust from the woodshed around their bed, in the fond, organic faith that slugs hate crossing a scratchy, unstable barrier (holly leaves, salty seaweed, chimney soot, sand, crushed eggshells, hair, and hawthorn clippings all figure in the litany of such materials).

Just in case, however, (here is further discredit, after last week's Roundup revelations) I left a thin strewing of blue metaldehyde slug pellets under the weed-suppressant fabric between the rows.

Metaldehyde is a chemical derived from ethyl alcohol (like the little tablets you burn in picnic stoves) which fades into carbon dioxide and water after two to three weeks on the soil. It certainly kills slugs and snails, but many people believe the pellets will harm song-thrushes, blackbirds or hedgehogs that eat enough of the poisoned molluscs.

Britain's Royal Society for the Protection of Birds has sought government help in funding research to find out how true this is, pointing to reports from the government's Wildlife Incident Investigation Scheme that hedgehogs, badgers and gamebirds have all been poisoned by metaldehyde. Dogs, too, have died after eating the pellets in quantity.

The manufacturers deny there is any problem, if the pellets are properly used (scatter thinly, keep away from pets, etc).

One reassuring website speaks of an investigation - unsourced - that found that hedgehogs could eat up to 200 pellet-poisoned slugs in a night "with no ill effects". My own doubt on this score is why I confine the pellets to beds closely covered with Bionet (proof even against the entrance of root fly), and the ubiquitous fabric mulch.

Thrushes and blackbirds skitter around the house in reassuring numbers, from a garden still thronged with little bite-size snails (the big, so-called "garden" snails, Helix aspersa, have colonised the lime-rich dunes along the shore). We are missing our hedgehogs lately, but badger gouges in the lawn suggest a more probable hazard than a surfeit of shrivelled slugs.

There is, of course, biological control of slugs, at a cost which is beginning to seem reasonable. Fruit Hill Farm, the organic supplier based in Bantry, Co Cork (e-mail:, is offering the slug-killing parasitic nematode Phasmarhabditis, whose microscopic hordes are watered into the soil in moist conditions and are active for at least eight to 10 weeks. Enough to control some 40 square metres costs €29.80.

While gardeners agonise over the harm they may do to wildlife (those saucers of beer do, indeed, trap slugs, but also the ground beetles that are their natural predators), the wider world of tillage continues to live by its own rules. Teagasc brought in a Scottish expert this spring to advise potato growers on how to avoid slug damage. Much of his advice was irreproachable: sow slug-resistant varieties such as Pentland Dell and Desiree, and don't leave potatoes in the ground in the autumn.

But scattering pellets was still the expert answer; the more applications the better, and be sure to get one in before the rows close over, or they'll just bounce off the leaves.

There are, however, organic potato growers who don't use pellets, herbicide or 10-10-20 fertiliser. To explore the alternative world of "green" products, try a new Irish website: