Slugs and Snails
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Overview:
Slugs and Snails attack many garden plants, although Snails are not quite as damaging as Slugs.
Britain climate is ideal for a broad range of slugs and snails species.
Its cool, damp summers and warmish, wet winters allow slugs to breed and feed for much of the year.
Snails in contrast, hibernate during the winter by sealing themselves within their shells whereas, slugs are more cold hardy and remain active in all but freezing weather.
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.
Black Slug:
The Black Slug can be very large, growing up to 200mm (8")in length.
Black is the most common form but it can come in various colours e.g. white, red, orange or grey.
They have no keel, and the skin is coarse and granular.
The sole is pale, sometimes orange, and the mucus is white.
When disturbed this slug may rock from side to side!
This slug is familiar to all gardeners usually because of its spectacular size.
It is usually not as destructive as the other three species, but it can cause damage in spring to many kinds of seedlings.
This is propbably because this is all the feeding material that is available.
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:
The Field Slug grows up to 40mm (1¾") in length, 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 lettuce and cabbage.
It will feed on many crops e.g. Carrots and Beans, Spinach, Celery and Tomatoes to Orchids and Cactii.
It is a major pest of cereal crops and will even eat potato haulms.
Garden Slugs:
Garden Slugs are a group of small blackish slugs that grow up to 30mm (1¼")in length, with a greyish side stripe.
They have no keel and are distinguishable from similar species by their rounded cross section.
The sole and mucus is yellow or orange.
Typically they attack the stems of young beans or marrow plants at ground level.
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:
The Keel slug grows up to 60mm (2½") in length.
They are usually dark grey/olive in colour, they have a keel, and a yellow or orange stripe along the ridge.
The sole is pale, and the mucus iscolourless.
Typically it curves into a sickle shape when disturbed.
A burrowing specialist, notorious for its destruction of Potatoes.
It will 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, and can also damage roots, tubers, bulbs and corms below ground.
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.
Generally:
Slugs are encouraged by mild, moist conditions and are most active in spring and autumn.
They are usually abundant in soils with a high organic content and are favoured by mulching and by heavy applications of organic manures.
Control:
Overuse of Plug 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.
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:
- Rock granules, crushed shells, copper tapes or copper-impregnated mats.
- Slug Baits, based on the chemical methiocarb can be effective.
- 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.
- Lay the product/s under cover in gardens where pets or young children are present.
In each case products should be be used sparingly to prevent other animals consuming it.
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 dipping the container in basins/buckets of water.
- Handpicking can greatly reduce slug and snail numbers.
Carry out this exercise about two to three hours after sunset when they are active.
They are usually more active in damp weather.
A torchlit walk around susceptible plants after dark will allow you to pick them up when they are feeding.
Other Methods:
- Construct hiding places for them for them to crawl under each morning e.g. upturned pots, planks of wood, this makes them easier to find during daylight hours.
- 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.t
- 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.
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.
Biological Control:
Use pathogenic nematodes.
These nematode only attack molluscs and have 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.
The nematodes are best applied from spring through to autumn.
Water them into the soil while it is moist, and in a temperature range of 7°-20°C (45°-68°F)
This microscopic eelworm then enters the body of slugs and infects them with a fatal bacterial disease.
Clear up the dead slugs after they have been affected to prevent other wildlife eating them.
This might prove difficult so perhaps a good place to distribute the nematodes is under upturned pots, planks of wood or at the base of hedges.i.e. anywhere the slugs might roost during daylight hours.