GARDENING: How to handle a slug problem

PUBLIC ENEMY: Above, the black slug. Below, this hosta has been ravaged by snails.
PUBLIC ENEMY: Above, the black slug. Below, this hosta has been ravaged by snails.
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SLUGS and snails are the bane of my life and this year has been exceptionally bad.

These soft-bodied molluscs are most active after dark or in wet weather, and their slime trails and holes in plant tissue, made by their rasping tongues, will tell you of their presence.

A snail-ravaged hosta.

A snail-ravaged hosta.

They’re surprisingly good climbers. Snails are less common than slugs in acid soil areas and, unlike slugs, remain dormant over winter, huddling together in protected places.

Reproduction happens mainly in autumn and spring, when clusters of spherical, yellowish-white eggs can be found under logs, stones and pots.

Common-sense preventive measures include transplant sturdy plantlets grown on in pots, rather than young vulnerable seedlings, protected with cloches; rake over soil and remove fallen leaves in winter so birds can eat eggs; go out with a torch on mild, damp evenings and pick them off your crops.

One biological control is Nemaslug, available in the form of a microscopic nematode or eelworm that is watered into the soil. The nematodes (Phasmarhabditis hermaphrodita) enter slugs’ bodies and infect them with bacteria that cause a fatal disease.

Moist, warm soil (temperatures of 5-20ºC) is required, so it’s most effective during spring to early autumn. Best results are achieved by applying in the evening; control may be less successful in heavy soils. It is unlikely to control snails, as they spend their time at or above soil level.

Another control method is to encourage wildlife – gastropod predators include thrushes, hedgehogs, ground beetles, toads, shrews and slow worms, plus domestic chickens and ducks.

SPRAYS

GARLIC SPRAY: Crush two large garlic bulbs in a plastic bag with a rolling pin. Add crushed garlic to one litre of boiling water, simmer for two or three minutes. Once cool, strain the liquid through an old jelly bag/stockings into jars.

This liquid is concentrated – use two tablespoons in a 10-litre watering can and with a fine spray rose, water the leaves of your plants out of direct sun. Use every 14 days.

VINEGAR: Mix equal parts vinegar and water and spray it on snails/slugs.

AMMONIA: Use one part ammonia to four parts water in a spray bottle.

BARRIERS

COPPER: Slugs and snails get static electric shock when they cross copper tape – make sure it is the widest you can buy. Effective, but expensive. Stand containers on matting impregnated with copper salts.

SANDPAPER: Make sandpaper collars to put around your plants – cut circles with a central hole from sheets of sandpaper. Cut a slit to the middle and pop it around the stem, laying the disc on the ground.

MINT/SAGE: Putting either or both of these herbs in your mulch acts as a repellent.

ROOIBOS/RED BUSH TEA: Used tea leaves deters gastropods and fertilizes plants.

SHARP BARRIERS: Eggshells, cinders, bark chippings, hair, pine needles, sharp sand, steel wool.

DESICCANTS: Ash (from wood fires), sawdust, cornmeal, raw oats, bran – dries out the creatures.

DIATOMACEOUS EARTH: A fine powder of crushed fossilised sea algae. The sharp edges are like tiny razor blades to the underside of a slug.

VASELINE/WD40: Smear/spray a 5cm band around the rim of pots.

TRAPS

BEER/YEAST & HONEY/GRAPE JUICE: Put out a large yoghurt pot half full of stale beer, boiled yeast and honey, or old grape juice. Sink it into the ground so the lip of the pot is at ground level. Slugs and snails will fall into the mixture and drown.

PEELINGS: Place upturned half orange, grapefruit or melon skins, or inverted cabbage leaves near vulnerable plants. Check daily.

MILK: A beer trap alternative, but keep it covered if you have hedgehogs in your garden.

DRY DOG/CAT FOOD: Cut notches in a tin foil pie plate and put dry cat or dog food in the soil. Cover with the plate upside down, lightly weighed down.