Slugs & Snails attack many garden plants, although snails are not quite as damaging as slugs.
Britain climate is ideal for a broad range of slug species, for the cool, damp summers and warmish, wet winters allow slugs to be active, breeding and feeding for much of the year.
Only snails hibernate, sealing themselves within their shells, whereas, slugs are more cold hardy & remain active in all but freezing weather.
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There are around thirty species of slug in the UK but only a minority pose any serious problem.
The four worst and most numerous are; the Black slug, Field slug, Garden slug and the Keel slug.
The black slug; can be very large, growing up to a length of up to 200mm (8").
Black is the most common form but it can come in various colours e.g. white, red, orange or grey.
There is no keel, and the skin is coarse and granular.
The sole is pale, sometimes orange, and the mucus is white.
The black slug may rock from side to side when disturbed!
Familiar to all gardeners because of its spectacular size, the black slug is rarely as destructive as the three other species but can cause damage in spring to many kinds of seedlings..
Later in the season, when its preferred diet of rotting vegetation, fungi, manure and even dead animals is more readily available, it causes little damage in the garden.
The field slug; is smaller, growing up to 40mm (1¾") and is usually grey /fawn in colour with darker flecks.
It has a short truncated keel or ridge on the back at the tail end.
The underside, or sole, is whitish with a darker zone along the centre.
The mucus is colourless or white.
The field slug is a surface-feeder typically found infesting leaf vegetables such as; lettuces and cabbages.
In fact it eats most crops e.g. carrots and beans, spinach, celery and tomatoes to orchids and cacti.
It is a major pest of cereal crops and will even eat potato haulms.
Garden slugs; are a group of small blackish slugs up to 30mm (1¼"), with a paler side stripe.
They have no keel and are distinguishable from similar species by their rounded cross section.
The sole is yellow or orange; the mucus the same colour.
As burrowers and surface feeders, the garden slugs attack both leaf and root crops.
Typically they attack at ground level, severing the stems of young beans or marrow plants for example.
They will also climb up and attack the heads of cauliflowers and many other plants or burrow down to eat the roots of turnips or beetroot.
It is a major pest of potatoes attacking both tubers and foliage and has been known to penetrate the soil to as much as a metre deep so nothing is safe from this slug.
The keel slug; is a larger species up to 60mm (2½") long.
Usually dark grey/olive in colour, it has a keel, with a yellow or orange stripe along the ridge.
The sole is pale, the mucus colourless.
Typically it curves into a sickle shape when contracted.
A burrowing specialist, notorious for its destruction of potatoes, it will in fact attack most root crops and is difficult to control as it spends most of its time underground.
Breeding; occurs in late summer / autumn when they lay clusters of white or pale yellow spherical eggs, up to 3mm (1/8”) in diameter in the soil, the heaviest infestations generally occur on soils covered with dense vegetation.
Young slugs and snails; feed mainly on decomposing plant material, but as they reach maturity, they eat an increasing amount of living foliage.
They feed at night, eating holes in leaves, stems, buds and flowers above ground; below ground they damage roots, tubers, bulbs and corms.
They hide under pots, seed boxes, stones and plant debris during the day, but the slime trails they leave indicate the extent of their nocturnal activities.
Slugs are encouraged by mild, moist conditions and are most active in spring and autumn.
They are generally abundant in soils with a high organic content and are favoured by mulching and by heavy applications of organic manures.
Control;
- Overuse of slug poisons can be counter productive in that you risk killing off the predators that are helping to control your slug population.
Such poisons should therefore be used, if used at all, only when and where a serious problem is seen to be developing,
Once you have identified the species and learn a little about its habits, you might well find that there are non-chemical options that are effective controls.
The most common control;
- Is metaldehyde; which may be applied as a solution.
This is sprayed or watered on to plants and soil,
It can also be pre-mixed with bran or bone-meal to produce a poisonous bait.
Metaldehyde is not always effective, and many slugs may recover from metaldehyde poisoning.
Affected slugs and snails should be collected and destroyed while they are still stunned.
Other products available are;
- Rock granules, crushed shells, copper tapes or copper-impregnated mats.
- Slug baits, based on the chemical methiocarb, kill slugs more effectively.
- Crystals / granules containing aluminium sulphate are relatively non-toxic if eaten by pets.
- A ferrous phosphate based (ferramol) it is less toxic to pets and wildlife than metaldehyde.
In each case these products must be used sparingly to prevent other animals consuming large numbers, or hidden under covers in gardens where pets or young children are present.
Non chemical control;
- Don't overfeed young plants in spring, as this only encourages soft growth, which slugs love to eat.
- Water the garden in the morning, rather than the evening, damp soil makes it easier for the nocturnal molluscs to move around.
- Water at the roots if possible to keep the ares around plants relatively dry.
- Water container plants by dipping them dip potted in basins/buckets of water.
- Handpicking can greatly reduce slug & snail numbers.
- They are are especially active two to three hours after sunset, particularly in damp weather.
- A torchlit walk around susceptible plants after dark will allow you to pick them up when they are feeding.
- Construct hiding places for them e.g. upturned pots, planks of wood for them to crawl under each morning. This makes them easy to find each day and dispose of.
- Place strategic heaps of sweet bran under /around highly susceptible plants.
- Encourage natural predators such as frogs, newts and toads,by perhaps forming a pond.
- Create homes for slowworms, hedgehogs and shrews to rest in and overwinter.
- Winter digging will expose eggs for various birds to feed on.
- Use of traps such as jam jars or proprietary traps sunk into the soil, and part-filled with beer or black treacle diluted with water.
- Protect plants in containers by placing a copper barrier tape around pots, or standing them on copper-treated fabric.
- Their food is located by smell, so drenching an area with a pungent smelling washes e.g. Jeyes fluid may deter them.
- A coffee solution sprayed on plants or watered over the soil can repel or kill slugs and snails.
A spray solution of 0.1 percent caffeine (a cup of instant coffee contains about 0.05 percent caffeine) will repel slugs, and a solution of 1-2 percent will kill them.
It is not known how caffeine kills the molluscs, but it seems to damage the nervous system.
Applications can cause leaf-yellowing on some types of plants.
Note; The Food and Environment Protection Act 1986 makes it illegal to use any chemical as a pesticide in Britain unless it has been approved for that purpose.
This applies to all would-be pesticides, even something as innocuous as coffee.
Alternatively;
- Use pathogenic nematodes.
The nematodes are best applied from spring through to autumn.
These microscopic eelworms enter the bodies of slugs and infect them with a fatal bacterial disease.
They are watered into the soil while it is moist, and in the temperature range 7°-20°C (45°-68°F)
The nematode only attacks molluscs and has no effect on other animals.
They are sold in some garden centres from chilled cabinets, or can be obtained from mail-order suppliers of biological controls.