Slugs

What are Slugs?

Slugs are part of the molluscs group of animals making them closely related to cockles, mussels, squid and octopus. They are soft bodied animals with no internal skeleton. They specifically belong to a group called gastropods, a name which quite literally means 'Belly Feet' which is quite appropriate for animals which move around on a 'foot' beneath their belly! Slugs have evolved from snails after the reduction of or complete loss of shell.

There are a number of varieties of slugs which are common in gardens. They are all different in size and their colour, ranges from yellowish grey, orange through shades of brown to black.

Do they harm plants?

Yes, although most feed on decaying matter rather than fresh.

What damage do they cause?

Above and below ground, slugs left to their own devices can strip young plants and seedlings to a stump overnight. They leave irregular shaped holes with smooth edges on leaves and leave a tell tale give away, slime trail. (This could also be snails).

On potatoes, holes are seen in the skin hiding larger cavities within the potato flesh. By the time the potatoes are lifted however, the slugs have usually disappeared back into the soil.

Do they affect certain plants?

Seedlings and other plants with new soft growth are particularly affected but generally many ornamental plants and vegetables are affected. Hosta leaves are particularly sought after with the plant earning the name of ‘Slug magnet’ quite readily. Potato tubers and tulip bulbs are also targeted.

Is there any time of year particularly at risk from slugs?

Although slugs eat plant material all year round, they are particularly a problem in Spring. This is due to warmer temperatures and damp conditions which are ideal for them to flourish.

How do I get rid of them?

Non-chemical control

Nematodes have become an increasingly popular way of dealing with slugs. This is a form of biological control (Phasmarhabditis hermaphrodita) that you mix with water which is watered into the soil which in turn is taken up by the slugs and infects them with harmful bacteria which causes them to die. Particular conditions are needed use this method i.e. temperatures of 5 to 20C in early autumn applied to moist but well drained soils under a full moon. Only joking about the full moon but it is worth checking the instructions to get the best from them.

The business of slug mass murder is a popular sport in gardens and as such many ways of extermination has been tested and re-tested.

In my experience, there are three main ways to reduce the slug population in your garden:

Plants, especially varieties of Hosta benefit from being grown in pots where the leaves do not touch other plants or hard landscaping features.
Go out on a damp evening in Spring and physically pick the slugs off the plants. Do this a couple of nights on the run and it will significantly reduce the problem in your garden.
Encourage predatorily wildlife into your garden like hedgehogs, frogs and toads, birds, slow worms and ground beetles.

Other people will swear by many other tips and techniques which include the following:

Beer traps either home made from jam jars sunk in the ground or bought ones that sit on the soil.
Grapefruit or melon skins upturned on the soil near ‘at risk’ plants. (Check each morning).
Protect seedlings or freshly transplanted plants with a clear plastic bottle ‘cloche’.
Physical barriers: Copper tape around pots, eggshell, grit, copper impregnated matting. Oatmeal around plants is said to attract them and when they eat it expands killing the slug. Oatmeal however easily gets wet though and needs to be refreshed on a regular basis.
Slugs lay their eggs in autumn/winter under wet leaves so turning them over with a rake enables birds to get ant them easily and eat them.

Chemical control

Slug pellets are generally the chosen form of attack in gardens and their green-turquoise pellets are seen all over the country in an effort to stop slugs eating prized plants.

If you feel you have to use slug pellets or a liquid form of pellet read the instructions first as using them not as advised will have no effect on the slugs. They need to be spread thinly around the vulnerable plants and seedlings.

Pellets based on metaldehyde generally are not harmful to wildlife, pets or children unless eaten in quantities but it is worth thinking about the implications of eating larger quantities by pets or children for example. Severe abdominal pain, nausea, vomiting, diarrhoea, fever, convulsions, coma, and persistent memory loss and in extreme cases; unconsciousness and eventual death has been recorded. Pellets based on aluminium sulphate and ferrous phosphate are less toxic but natural methods ideally would be a first choice.

Most plants once they have chance to establish are able to resist damage from slugs unless there is a particularly large population.

Always use chemicals as instructed on the label and wear any gloves etc. when necessary.