Advice
RHS Help & Advice
Slugs (many species)
Plants affected
A wide range of vegetables and ornamental plants, especially seedlings and other soft growth.
Symptoms
Soft succulent growth, including seedlings, young tender shoots, leaves and flowers are damaged or eaten, particularly in wet conditions. Underground parts of plants, especially potato tubers and tulip bulbs are tunnelled by black keeled slugs (Milax spp.). Slime trails may be visible near the damaged tissues. See also Snails.
Cause
There are about seven species of slugs that are garden pests. They can do damage throughout the year on a wide range of plants, but seedlings and new growth on herbaceous plants in spring are most at risk and may need protection. Most slugs live in or on the soil surface, but keeled slugs (Milax species) live and feed mostly in the root zone. Slugs vary in size from the smaller Deroceras reticulatum (grey field slug, buff coloured form, right), which is no more than 5cm (2in) long, to Arion ater (large black slug, left), which can be 12cm (5in) when fully extended. Some slugs vary in colour; Arion ater can be black, orange brown or buff coloured. Warmer weather combined with damp
conditions greatly increases their activity.
Slugs remain active throughout the year, unlike snails, which are dormant during autumn and winter. Reproduction occurs mainly in autumn and spring, when clusters of spherical, yellowish-white eggs can be found under logs, stones and pots.
Slugs are most active after dark or in wet weather.
Control methods
Slugs are so abundant in gardens that some damage has to be tolerated. They cannot be eradicated so target control measures on protecting the more vulnerable plants such as hostas and young vegetable plants.
There are a number of non-chemical and chemical controls you can choose.
Non-chemical control
A biological control specific to slugs, with no adverse effect on other types of animal, is available in the form of a microscopic nematode or eelwom 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 soil and soil temperatures of 5-20oC are 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.
Other preventive measures you can take include:
- Transplant sturdy plantlets grown on in pots, rather than
young vulnerable seedlings. Protect transplants with plastic
bottle cloches.
- Place traps, such as scooped out half orange, grapefruit
or melon skins, laid cut side down, or jam jars part filled
with beer and sunk into the soil near vulnerable plants.
Check and empty these regularly, preferably every morning.
Proprietary traps are available from garden centres.
- Place barriers, such as copper tapes (Fito Slug Stoppa Tape, Agralan Copper Slug Tape, Growing Success Slug Barrier Tape) around pots or stand containers on matting impregnated with copper salts (Slug and Snail Shocka,
Agralan Slug and Weed Mat). Moisture-absorbent minerals can be placed around plants to create slug barriers (New Horizon Natural Slug Barrier, Fito Slug Stoppa, Growing Success Slug Stop, Vitax Slug Off, Gem Slug n Snail Repellent). Gel repellents (Westland Slug Blocker Eco Barrier Gel, Greenfingers Slug Defence Gel) can also be used to create barriers around plants. All of these products are available from garden centres.
- Go out with a torch on mild evenings, especially when
the weather is damp, and hand-pick slugs into a container.
Take them to a field, hedgerow or patch
of waste ground well away from gardens, or destroy
them in hot water or a strong salt solution.
- Some birds, frogs, toads, hedgehogs, slow-worms and ground
beetles eat slugs and these predators should be encouraged
in gardens.
- Rake over the soil and remove fallen leaves during winter so birds can eat slug eggs that have been exposed.
Chemical control
Scatter metaldehyde slug pellets (Scotts Slug Clear Advanced Pellets, Bio Slug and Snail Killer Pellets, Gem Superslug Killer, Westland Slug Buster Pellets, Westland Slug Attack Mini-pellets, Doff Advanced Slug Killer or Doff Slugoids Slug Killer) thinly around vulnerable plants, such as seedlings and young shoots on herbaceous plants. A liquid formulation of metaldehyde (Scotts Slug Clear) is available for watering on to ornamental plants and the soil. Pellets may harm other wildlife, pets and young children if eaten in quantity, although slug powders based on aluminium sulphate (such as Doff Slug Attack) are less toxic. A relatively new form of pelleted bait containing ferric phosphate (Growing Success Advanced Slug Killer) is also relatively non-toxic to vertebrate animals.
Most plants, once established, will generally tolerate slug damage and control measures can be discontinued.