Slugs are so abundant in gardens that some damage has to be tolerated. They cannot be eradicated so targeting control measures to protect particularly vulnerable plants, such as seedlings and soft young shoots on herbaceous plants will give the best results.
A biological control ('Nemaslug') specific to molluscs, with no adverse effect on other types of animal, is 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.
A moist warm soil (temperatures of 5-20ºC (41-68ºF)) is required, therefore control is most effective during spring to early autumn. Best results are achieved by applying in the evening to moist but well-drained soils; control may be less successful in heavy soils, such as clay. The nematode is available from refrigerated cabinets in some garden centres or by mail order from suppliers of biological controls (download pdf below).
Other non-chemical controls
There are many preventive measures that have been used by gardeners to minimise slug damage. Most of these do not have any scientific evidence to prove that they are effective. These measures include:
- Transplanting sturdy plantlets grown on in pots, rather than young vulnerable seedlings. Transplants can be given some protection with cloches
- Torchlight searches on mild evenings, especially when the weather is damp; hand-picking slugs into a container. They can then be taken to a field, hedgerow or patch of waste ground well away from gardens, or killed in the freezer before being added to the compost heap or put in the bin
- Some birds, frogs, toads, hedgehogs, slow-worms and ground beetles eat slugs and these predators should be encouraged in gardens
- Raking over soil and removing fallen leaves during winter can allow birds to eat slug eggs that have been exposed
- Traps, such as scooped out half orange, grapefruit or melon skins, can be laid cut side down, or jars part-filled with beer and sunk into the soil near vulnerable plants. Check and empty these regularly, preferably every morning. Proprietary traps are also available from garden centres and mail order suppliers
- Barriers, thought to repel slugs, include rough or sharp textured mulches and substances thought to be distasteful or strong smelling. Copper-base barriers have been shown to repel slugs in some studies. A recent RHS study in a garden-realistic scenario however, found no reduction in slug damage from barriers made of copper tape, bark mulch, eggshells, sharp grit or wool pellets
Most of these non-chemical control options have very little scientific research into them, but the RHS is hoping to address this knowledge gap and is carrying out a range of scientific studies.
Potatoes and slugs
The slugs that damage potatoes spend much of their time in the soil where they do not come into contact with slug pellets. The nematode treatment (see above) can be effective. Damage usually begins during August and becomes progressively worse the longer the crop is left in the ground. Early potatoes usually escape damage; maincrop potatoes should be lifted as soon as the tubers have matured if the soil is known to be slug infested. Heavy applications of farmyard manure and other composts can encourage slugs, and so inorganic fertilizers should be used where slugs are a problem.
Potatoes vary in their susceptibility to slugs. ‘Maris Piper’, ‘Cara’, ‘Arran Banner’, ‘Kirsty’, ‘Maris Bard’, ‘Maris Peer’, ‘Kondor’, ‘Pentland Crown’ and ‘Rocket’ are frequently damaged, whereas ‘Romano’, ‘Pentland Dell’, ‘Pentland Squire’, ‘Wilja’, ‘Charlotte’, ‘Golden Wonder’, ‘Kestrel’, ‘Estima’, ‘Stemster’, ‘Sante’ and ‘Pentland Ivory’ are less susceptible. Damaged potatoes are more vulnerable to storage rots and the crop should be sorted into sound and damaged tubers, with the latter being stored separately for early consumption.
Following the manufactures instructions scatter slug pellets thinly around vulnerable plants, such as seedlings, vegetables and young shoots on herbaceous plants. It is important store pellets safely and scatter them thinly as they can harm other wildlife, pets and young children if eaten in quantity.
There are two types of pellet available to the gardener; those that contain metaldehyde (e.g., Ultimate Slug and Snail Killer, Deadfast Slug Killer, Doff Slug Killer Blue Mini Pellets, Westland Eraza Slug and Snail Killer) or ferric phosphate (e.g. Growing Success Advanced Slug Killer, Solabiol Garden Slug Killer, Vitax Slug Rid, Doff Super Slug Killer, Sluggo Slug & Snail Killer, SlugClear Ultra3). Ferric phosphate is approved for use by organic growers. To protect children and pets pellets must be used as directed.
Inclusion of a pesticide product does not indicate a recommendation or endorsement by the RHS. It is a list of products currently available to the home gardener
Most plants, once established, will tolerate some slug damage and control measures can be discontinued.
Pesticides for gardeners (Adobe Acrobat pdf document outlining pesticides available to gardeners)
Biological control suppliers (Adobe Acrobat pdf)