Snails and slugs are horribly damaging and we should waste little energy admiring the evolution of the latter in casting off the shells enjoyed by their snail ancestors.

Snails are restricted to more alkaline areas, where they use calcium to construct their shells, but slugs have less weight to cart around, can live almost anywhere and no crack is too small to stop them slithering towards your precious plants.

Slugs are an all-year round problem and you should never drop your guard. In winter, I invite my ducks into the vegetable garden to help me out. Muscovy ducks are my finest foragers, but any questing beak will do. Thrushes, robins and blackbirds are just as good.

Even in winter, I keep my beer traps topped up with dregs from my homemade beer bottles. With such good beer, I can always rely on a few discerning visitors. Every drowned slug dents next year's population. If you don't brew your own, splash out on some cheap cans of beer for your Slug X beer traps. Slugs also congregate beneath the traps, so check there too. And put wooden boards or larger plant pots in different places. Slugs shelter in these damp, seemingly safe havens.

Since even the tiniest slug has a radula bristling with 2,000 tiny teeth, a tray of lettuce is no challenge. As we know to our cost, young seedlings are their favourites. Molluscs share our preference for tender young leaves, largely because they're safer to eat. They won't contain the toxins that some wild plants have developed as protection against herbivores. Our domesticated varieties are even more alluring as toxins have been bred out of them.

A keen sense of smell is an important weapon in the mollusc armoury. Large Arion species have even been seen rearing up off the ground, almost as if they were sniffing the air. They'll track down a row of turnips or carrots the second they germinate. And distance is no object. Slugs travel large distances for a meal and surmount seemingly impossible hazards.

So how can we combat all this? Vigilance is undoubtedly the most effective control when plants are young and succulent, a nightly patrol catching these greedy grazers. Disconcertingly, they'll happily eschew your tender leaves if they can indulge in a bit of cannibalism. One dead mollusc will attract many others from far and wide.

Desperate gardeners have tried lots of barriers - crushed egg shells, soot, grit and the rest. Unfortunately, they're a waste of time. Over several years at our demonstration organic garden in the Borders, we tested several of them and found them as useless as Which? Gardening did in one of its recent trials. A very poor performer was the brand Slug Be Gone, whose granules - designed to remove moisture from slugs as they plough through them - we sprinkled round plants. After rain, though, the granules became soggy and so were no impediment. We also found slugs took soot and egg shells in their stride.

Unlike Which?, I find copper tape provides good protection for container-grown plants. In my experience, the control only fails when leaves grow over the barrier, thereby providing a bridge into a plant. Slugs can also enter a pot through drainage holes.

The biological control Nemaslug is the most effective weapon, when used properly. It's estimated there may be a million different species of nematode, microscopic worms one of which is used in Nemaslug. It enters the mollusc and disrupts its gut, thereby killing it. The treatment is easy to use. Put the paste containing nematodes in a watering can and spread over a target area. Only do this when the soil is damp or wet. The molluscs should be completely eradicated within six weeks.