The Gardeners' Foe: dealing with slugs

I have not seen molluscan enemy number one-yet. Apparently it arrived in southern England on imported produce and has been taking over the slug world.  Ariston vulgaris, a large orange Spanish slug, has been gobbling soft fruit and certain vegetables in Europe, and now it is here. This slug breaks the rule that it is the small slugs that gardeners should fear,  for they are the ones that eat vegetables; the large ones generally feast on compost, which is why I often find them in my compost bin. But Ariston vulgaris is not only big and mean, it's great at mating, not only hybridizing with certain native varieties of the Ariston genus, but producing more eggs than they do. I am in the North West,yet unreached by the continental intruder, but I am keeping my eyes open. It's a matter of time.

I am careful which pellets I use. Poisonous ones containing metaldehyde are a no-no. This poisonous substances remains in slug guts after the slug has been eaten, so the metaldehyde poisons the hedgehogs that eat the slugs,and it has been responsible for catastrophic decline of Britain's hedgehog population,along with other factors. I have spoken to an elderly gardener who says that he has flinched as he listened to the pitiful wails of hedgehogs poisoned by slug pellets,so   I prefer a non-poisonous pellet made of wool, which the slugs eat only for it to swell up and block their guts, preventing feeding. Hedgehogs  and birds are not affected by these ones.

Ferrous phosphate has been touted as a harmless [to humans and  dogs] component of slug pellets, but to make it poisonous to slugs it needs to have the addition of EDTA, a poisonous chemical in small quantities. I do not think it as harmful as metaldehyde or methiocarb, but I am not fully certain about it,so I stick to wool based pellets. Pellets made of aluminum phosphate are said to be safer to animals, but there are fears about their adding aluminum to the soil, as it is toxic to plants in significant quantities.

Pellets are basically bait, and there is another form of bait that has been often used:beer. Slugs are basically tipplers who love beer and ale, so much that they "dive" into containers of it and drown. It's not the worst way to die! The technique is to dig a small container into the ground, half fill it with beer and wait overnight. If the weather is wet a covering that allows slugs to get in but prevents rain from diluting the bait is useful. You will find dead slugs in the morning, but console yourself that they had a happy death. But beware, suicidal slugs are fussy, as I once discovered. Having bought two cans of cheap lager for my slug traps, I had no slugs in the traps, but when I replaced the cheap lager with a quality bitter beer, the results were positive. The message is that slugs bent on self-destruction only tolerate quality beer!

The best defence against a pest is a predator, at least a predator that does not eat you! Insectivorous birds and mammals are ideal. In Britain we have the hedgehog, which is always welcome in wise people's gardens, but this species is in catastrophic decline, Environmentally conscious gardeners try to leave wild patches full of leaves, twigs  and grass for hedgehogs to nest, and it is regarded as a wise idea for their to be gaps in fences for them to pass through. They will set up residence then hunt nocturnally, feasting on slugs.

Birds can also be predators, so encouraging as wide a range of birds to nest in your garden is desirable. Ducks are wonderful slug killers, for they roam the garden gobbling slugs. Unfortunately, council regulations forbid the keeping of ducks on my allotment. But smallholder and gardeners are freer than I. What they often  do is go round at night with bucket into which they drop captured slugs. Then they take them to the duck enclosure. Slugs make a good addition to duck feed!

Yet another gardener' friend is the frog. I have a pond for frogs on my plot, and last year they spawned there. This year to my surprise I found toad spawn, which is just as good. Frogs and toads will hunt through your garden eating insects. They like to prowl the compost heap seeking slugs, so when you are turning compost often a frog or toad jumps out. You need a bit of wild space  for them to hunt, so a fully manicured garden is not what they like. They return to water to breed and moisten up, but they do not live in water as adults. In fact some years ago my neighbour lifted a tarpaulin and found a rather fat toad with the remains of several slugs around him. We could see how he had become so large!

Another predator is a nematode, Heterorhabditis. This is a microscopic, wormlike  creature that gardeners spray on their land every few weeks after the soil temperature has risen to five degrees celsius or more. It burrows through the soil and on finding a slug burrows into its neck, paralysing the nervous system, whereupon it feeds. Nature is not always very nice. These nematodes are members of the Rabdita order, and the genus Heterorhabditis is characterized by being an obligate parasite on insects and molluscs. These  nematodes have a wide application in gardening, and they can be purchased from specialist sellers. Currently I am having to wait to apply them as the soil temperature in Britain is too low at the moment due to inclement weather.

Nematodes do not work with snails. The other predators are however effective against them. 

Integrated pest management is a technique in which gardeners and farmers use a co-ordinated system of tactics and tools to overcome pest threats. Along with the techniques outlined above there are cultural techniques, what the gardener does with his/her tools and time.

One technique is to lay a tarpaulin or carpet overnight. The slugs will gather under this and in the morning lift it to pick them up. This tactic works best when you can throw them to the ducks or otherwise dispose of them, maybe by chopping them in half. Their bodies can be left on the compost heap or left out for birds.

Prevention is better than cure, and so it is considered good practice to maintain the garden so that debris and detritus is not left lying around, for slugs like to hide underneath it. You cannot eliminate all places in which slugs can hide, but you can minimize them.

When digging if you uncover small white eggs collect them and either drop them in water or place them on the bird table, where they will play their part in the cycle of nature, feeding avian predators.

There is discussion about gritty materials and their ability to deter slugs. I  have applied some  potash from the woodfire and have had no slugs on the area, though I also have wool pellets as well, so it is hard to say.  Some gardeners strew crushed egg shells around the plants to be protected, but this has not always been considered effective and rats like licking the insides of shells that contains egg residue.

Copper strips at the entrances to garden buildings are said to deter slugs, as their slime reacts with the copper to produce a slight electrical current, which gives them a shock. However, I  tried this technique in the kitchen of my previous house, but it did not work well.

Pouring salt upon slugs kills them quickly, but in large quantities it does not do your garden any good and it is better used on patios.

Sadly slugs and gardeners are enemies, and if left alone the slugs will strip your food crops bare, and the implication of this is that if we want to have food we have to suppress slugs. Even the most dedicated vegetarian gardeners need to deal with the slug problem. Dealing with pests is not the nicest side of gardening, but it is a  necessary process.