Pests & Diseases: Slugs and snails•
Posted on 18 January 2019
Slugs & Snails: what are we dealing with?
There are around 120 species of snail in the UK. These range from 1mm Dot snails (punctum pygmaeum) to the Roman Snail (Helix pomatia) which has a 5cm shell and is good with garlic butter. Some of these species are specific to geographical areas so not all will turn up on your plot. The main one we are interested in is the European Brown Garden Snail (Helix aspersa) - a terrestrial gastropod mollusc. These Gardens Snails have a life span of 2 to 6 year. They can produce up to six batches of eggs in a single year, and each newborn will take one to two years to mature.
Slugs evolved from terrestrial snails, they are basically a shell-less snail. A tiny number of species still have a small shell and the remainder have a vestigial shell inside them. There are around 40 species of slugs in the UK. No consolation when they're eating your lettuce but only a few of these are pests. Many species perform a key role in composting though releasing nutrients back into the ecosystem and helping your plot to grow. A slug can lay between 100-500 eggs in groups of 10-50, generally sheltered in a hole it digs. Slugs can produce up to two generations per year. They live between 9-18 months depending on the species and conditions.
Though it may feel like they travel in packs, slugs and snails are lone operators. They feed by licking your veg with a cheese-grater-like radula and can cause a lot of damage while your back is turned.
Ways to control slugs & snails
So we have established that they are a nuisance in the garden and can devastate your veg patch in a very short time but how do we deal with this? There are many ways, some of which involve total eradication. What the gardener should aim for though is control rather than a complete purge. What you are looking for is a balanced ecosystem within your space. Complete obliteration of every slug and snail will take away the good things they do like composting and lead to a vacuum which in time will draw more of them to your plot.
Block their path
For both slugs and snails mucus is essential for their movement. A gland situated at the front of the foot secretes mucus which is squeezed below the sole and allows them to slide along leaving the silvery trail we know so well. Because they move like this, putting something in their path to make their progress painful is very effective. So try one of these to make getting to your plants feel like walking on broken glass.
- crushed egg shells (bonus that they add calcium to your soil)
- used coffee grounds
- food-grade diatomaceous earth
- sheeps wool round the stems of tender plants
- Don't use salt. It will kill the slugs and snails but will also kill your plants.
Slug pellets: These get justifiably bad press. They certainly kill slugs and snails but also poison pets, children and the unfortunate predator that eats prey that has consumed one. I have put them first in this list to get them out of the way and hope that you will be able to find at least one better, more environmentally safe choice in what follows. Most slug pellets are not organic and even the organic ones are not wise to use: when the slugs die, the predators leave to find food elsewhere – leaving you in need of more pellets. And so it goes on...
Traps and Barriers
Trapping slugs and snails is a good way to stop them. Beer Traps:
This is the method that I use and it is hugely successful. Haxnicks Slug Buster buried a little way into the ground and filled with cheap beer will have them flocking. They are attracted to the smell of the yeast in the beer. Add some oats to make it even more enticing. The lidded design wins over home made traps as it stops the rain getting in and diluting the beer. It also creates the nice dark space that both slugs and snails look for. Hiding Place Trap: Alternatively set up a Hiding Place Trap. Slugs and snails like to hide in dark, damp spaces. Find a wet piece of wood or wooden plank. Place it near an area where snails and slugs are frequently spotted. The next morning, check the wooden plank and get rid of any attached to it. The same works with an upturned plant pot or hollowed out grapefruit half. Prop the edge up on a stone to allow them to crawl inside. Make sure to check the trap in the morning. Dispose of its residents otherwise all you have done is set up a campsite close to the buffet for the little critters! Copper: Slugs don't like to crawl across copper so putting a border of copper is supposed to prevent them. A variety of products are available such as copper tape to put round plant pots, mats to sit pots on etc. I have never had much luck with this method but it is widely used so you might want to try it.
Plant things they don't like such as rosemary, thyme and all sorts of mint If you need to cut back a prolific mint plant then you can also dig the clippings through the soil to further deter them. If you live by the sea then seaweed will also work in this way. Slugs and snails love Lawn Camomile. So rather than planting to deter them, plant this to attract them away from your seedlings- especially good if you want to collect the slugs to get them out of your garden as you know where they will be. The slugs that attack growing potato tubers live under the soil where you can't see them. So growing your potatoes in protected Potato Planters that you know are full of slug-free compost rather than in the ground may be an effective way to grow them whilst you get your slug problem under control.
Picking them off by hand - especially after dark while they are more active - is a sure fire way to get rid of them. Search for them under stones, wood and plant pots to seek out their most likely hiding places. The big issue with this method is how to dispose of them. Moving them just unbalances someone else's ecosystem but many find it hard to kill them. Drowning - in a jar of water, not a bucket as they will be able to climb out - works if you have the heart for it. Leave them in the open for birds to take. This will also encourage bird life into the garden. Ensure you have enough birds interested to do this though otherwise you will be meeting the same creatures every night.
Introduce a predator
Birds: Birds love slugs and snails so encourage birds into your garden by setting up a birdbath and feeding table. Or if you have room introduce chickens and ducks as they both LOVE a nice slug. So, introducing some birds to your plot will be a win win situation. Nematodes: This is the quick, effective and easy to do and will create a slug free area for up to 6 weeks. Nematodes are slug parasites. They are microscopic worms that kill slugs. You use them by watering on to the soil surface, where they search for prey and invade it. Special 'nematode food' bacteria, are released and multiply rapidly to nourish them and keep them working. An infected slug stops feeding in about 3 days before beginning to swell. The nematodes multiply inside the slug which starts to decompose and the new nematodes spread and start looking for their next prey. This treatment is so effective though that all slugs are eliminated. This means that the natural - non nematode predators - also disappear to look for food elsewhere. The garden now contains loads of slug food and no slug predators. So once it is rediscovered by the next generation hatching or itinerant slugs they will have free reign. Frogs and Toads: If you have room for a pond then keeping frogs in it will sort your slug and snail problem. Hopefully an obliging frog will come and spawn in your pond - check out local ponds to see if you have any living near by. If you don't have room for a pond then you could still have toads as they do not require a pool. As long as there are enough moist hiding spaces for them round the garden you should be OK. Other predators you might like to consider building habitat for are:
- Hedgehogs - contact your local rescue centre to see if your plot is suitable
- Carob beetles - eat eggs as well as grown ones so double whammy from these
- Centipedes - ensure you get carnivorous centipedes as oppose to herbivorous millipedes which will eat your plants
I wouldn't like to try it with slugs but the Common Garden snail is edible so if all else fails you could always eat them yourself!
Think like a slug
Water: Snails and slugs need a moist environment. They are generally more active at night for this reason. If you water your garden in the evening, you lay yourself and your veg open so they can glide toward your plants at a rate of knots. If you water your plants in the morning, the sunlight will dry the plants out before dark and make them less attractive to slugs and snails. Tidy plot: Keep your plot tidy and you can deter slugs and snails. Don't leave piles of pots, planks of wood and old watering cans around that they can use for shelter. Make sure beds are tidy with well spaced plants so that moving between lunch and dinner is harder for them. It will be an ongoing battle I am sure but hopefully there will be some new ideas here that help you to create a balance in your garden so that your seedlings make it through and you can successfully harvest some unchewed veg.
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