Cool, damp summers like this one are perfect for slugs. Unfortunately the recent run of foul summers has led to a massive increase in mollusc numbers and gardeners are faced with the almost insurmountable task of protecting plants against predatory slugs and snails. For many, what's even more galling is that, according to a publication for the European Commission, the south of Scotland is one of the most slug-ridden parts of Europe.
There are around 35 species of slugs and snails in the UK. The three most damaging are the blue/black garden slug, Arion hortensis; the field, or netted, slug, Deroceras reticulatum; and the keel or Budapest slug, Tandonia budapestensis. Garden and field slugs are expert consumers of lettuce and seedlings, while the grey/olive keeled mollusc, with an olive or orange keel on its back, specialises in potatoes. You rarely see this horror till you start howking your tatties, only to find a destructive network of tunnels through the tubers.
The weather over the past few years has been perfect for molluscs. Long, wet summer days allow garden slugs to survive until they lay around 80 eggs in the autumn. But this number pales into insignificance when compared with the field slug's annual tally of 300 eggs. Twenty years ago, one researcher, Dr A Smith, found 100 field slugs per square metre of his trial ground.
Mollusc numbers haven't been reduced by winter. A mild spell was ideal; any snow provided shelter; and the cabbage consumers managed to go deeper into the soil when the ground started to freeze. Their sense of self-preservation is all too reliable.
Instead of howling with impotent rage as precious crops and wonderful clematis succumb to this onslaught, you must develop strategies to confound these slithery pests, though I can offer no single solution.
You can protect some plants with copper tape – other barriers are a waste of time. The best approach is to reduce the population. Cultivating any bare ground in winter helps: this exposes slugs and their eggs to the watchful eyes of thrush and blackbird. I was delighted to see the European Commission report that recommended using ducks to work over vacant parts of the vegetable plot as no slug could escape their foraging beaks, though this is not a solution for most folk.
Molluscs attack seedlings, stressed plants and damaged leaves that are easy prey, so vigilance is paramount. This task often entails search-and-destroy moonlight patrols. On wet evenings, swathed in a midge net, I've embarked on torchlight forays. The simplest way to dispose of my massive haul is to squash under foot on a slab path. This also makes an excellent trap for the other slugs intent on consuming their less fortunate fellows. Small food traps are also effective and a beer-charged Slug-X trap works well.
For larger areas, the biological control Nemaslug is good and easy to use. During a wet spell, millions of microscopic nematodes are watered onto the ground. The tiny worms seek out the slugs and disrupt their victims' digestive system, thereby killing them. I have found this generally works well, but have also seen that molluscs living in the grass paths around my raised beds will still get to recently sown neeps. The nematodes may kill these pests within days but the damage may already have been done.
Given that even this treatment isn't completely effective, I was delighted when organic slug pellets were introduced a few years ago. Traditional slug pellets contain metaldehyde and are damaging to pets and wildlife. Ferric phosphate is the active ingredient of the new pellets and because this is safe for wildlife, I have recommended it in this column. However, research scientists Tamm and Speiser, from the Swiss Institute of Organic Agriculture, claim the new pellets should not be used by organic growers. They say a substance that softens the iron in the pellets and lets slugs absorb the poisonous metal is dangerous. Recent research by Clive Edwards and others from Ohio State University appears to confirm this. Edwards states: "Clearly, molluscicides containing iron phosphate and chelating agents may present significant environmental hazards to earthworms, domestic animals and humans and these issues need further investigation." The German manufacturer, Doff, will soon be launching slug pellets without the softening agent – this may be a safer option.
