Download Slugs and Snails – Alternatives to Molluscicides

What are Slugs and Snails?
Although an extremely diverse phylum, slugs and snails are the only molluscs to have
successfully conquered the land, making a wide variety of terrestrial habitats their
home. Despite their reputation, they have many natural predators, and it is likely
that they play an important role in litter decomposition and alteration of the soil
environment.
The Problem…
Throughout the UK, slugs and snails are considered significant pests of the
agriculture and gardening worlds, with methiocarb or metaldehyde containing
molluscicide pellets often being applied to
protect crops. These, however, typically
provide poor control and cause considerable
harm to domestic animals and other wildlife,
including important natural predators of these
‘pests’ - e.g. birds and hedgehogs. For
growers/gardeners, particularly those using
organic techniques, slugs and snails do present
a problem but, with a large number of
eco/environmentally friendly alternatives to
molluscicides available, a more sustainable
strategy for managing them IS possible!
A pest… or just misunderstood?
Are slugs and snails feeding on your patch?
With most damage occurring at night, look out for these tell tale signs to decide
whether or not action needs to be taken:
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Silvery slime trails over soil and plant surfaces.
Irregular shaped leaves – including larger leaves with holes and evidence of
munching from the margin.
Frequent attack of favourable spring plants such as lettuce, basil, and broccoli.
Fruit (e.g. strawberries) with holes.
Absence or very few hostas and delphiniums, as these ornamental plants are
particularly attractive and so are unable to thrive.
Disappearance or shortening of young shoots and seedlings.
Hollowing of root crops – entry via damage by other pests (e.g. wireworm).
Take control and say NO to molluscicides!
As concern over the little known long-term effects of molluscicides continues to
increase, it is important that the use of these eco-toxic chemicals is strictly
controlled - if not ceased!
Rather than eliminating all slugs and snails, methods of organic control aim to,
instead, restrict numbers present as a means of reducing damage. This therefore
helps protect both valuable plants and the local wildlife – so a potential win for all!
1) Create Unfavourable Conditions:
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Slugs and snails favour cool, shady, moist conditions for resting and laying eggs,
so try to reduce environmental appeal by planting in full sun.
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Increase space between plants to
enable air to circulate and further
expose the soil to the sun for more
rapid warming.
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Raised beds and application of
compost will also cause the soil to
dry out quicker.
These snails seem to like this spot!
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Reduce the availability of preferred shelter (stones, debris, weeds, mulch etc.).
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Slugs, in particular, are thought to avoid aromatic herbs and so should be
deterred by the interplanting of plants such as lavender, rosemary, thyme and
sage.
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Varieties of potato tuber such as Ambo, Romano, Sante and Cara are much less
vulnerable to attack by soil dwelling slugs – so choose your veg wisely!
2) Natural Barriers:
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Copper is very much disliked by slugs and snails, as the chemical reaction that
occurs within their bodies is comparable to an electric shock - Surround
crops/beds with copper mesh fencing or strips to prevent access. Note: Handpick slugs/snails already in the bed prior to barrier construction.
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Diatomaceous earth (*), along with wood ash, sharp sand, sawdust and pure coal
soot are also thought to successfully block entry. Note: Reapplication following
rainfall is required.
*Diatomaceous earth = non-toxic mineral product consisting of the fossilised shell
remains of diatoms (an algae) (Bradley and Ellis, 1997)
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Bottle Cloches – bottom cut off an empty plastic bottle:
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Considered one of the best barriers against
slugs.
Can be removed once plant has grown and is
less vulnerable.
(Image: Garden Organic, 2013)
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A ring of favourable wilted comfrey leaves encircling vulnerable plants will act as
an effective decoy.
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Sensory barriers, such as yucca plant extract containing sprays applied onto and
around plant/crops are a good repellent and handy for those hard to reach spots.
3) Biological Control:
With their numerous natural predators, encouraging a diverse, balanced ecosystem
will help to keep numbers in check and increase the biodiversity of an area.
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A single hedgehog may consume up to 500
slugs in a night! To encourage their
presence, provide water and cat/dog food,
as well as leaf/log piles or garden waste for
sleeping.
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Frogs and toads will inhabit wildlife ponds,
and the latter are also attracted by broken,
upside down clay pots.
A tasty snack for a hungry hedgehog!
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Encouraging birds such as the song thrush, with a declining UK population
(particularly in areas of intensive farming where snail numbers are low), also
offers significant conservation potential. To attract these, and other birds, it is
important to provide suitable places for breeding, shelter and hibernation – e.g.
bird boxes, trees and hedgerows.
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Parasitic nematodes have been found to offer efficient control of molluscs. They
are available commercially and act by burrowing into their specific prey and
consuming it from within. Note: Must be applied every 6 weeks and when the
soil is moist and weather conditions warm (> 5◦C).
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Rove beetles and ground beetles are both extremely effective natural predators
of slugs, feeding on both adults and eggs. Beetle banks and field margins offer
highly preferable habitats.
4) Additional Options:
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Hand picking should be used in combination with the methods described above.
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To collect when feeding,
attractants such as bran and
comfrey can be put down.
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Using upturned grapefruit halves
will also aid collection.
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For optimum results, it is
recommended that a variety of
control methods are employed.
Hand searching can be fun for ‘kids’ of all ages…
Final Thought…
Producing high quality crops and flourishing ornamental plants are the reasonable
aims of many food growers and gardeners, and it is not unfair of them to say that
some slugs and snails occupying their prized plots seem to have other ideas…
However, using toxic chemicals to eliminate this ‘problem’ is not a sustainable
answer and, with an array of effective, wildlife friendly alternatives available, it is
now possible to minimise plant damage whilst also promoting biodiversity and
permitting these misunderstood creatures to fulfil their own key ecological roles!
Thank you for taking the time to consider the fate of our slug and snail species and
please think twice before sprinkling those pellets on your patch!
Written by Amy Coyne (Sustainable Merton)
All images copyright of Amy Coyne (unless otherwise stated)
References:
Allison, F.E. (1973) Soil Organic Matter and its Role in Crop Production. Amsterdam:
Elsevier Scientific Publishing Company.
Bradley, F.M. and Ellis, B.W. (Editors) (1997) Rodale’s All-New Encyclopedia of
Organic Gardening: The Indispensable Resource for Every Gardener. United States of
America: Rodale Press, Inc.
Brooks, A. and Crook, M. (Date Unknown) ‘Mini Review - The Use of Molluscicides in
UK Agriculture and their Effects on Non-Target Organisms’. The Malacologist.
Available at: http://www.malacsoc.org.uk/malacological_bulletin/MiniReviews/2Molluscicides/molluscicide.htm
Cherfas, J. (1989) ‘The Killing fields (and gardens) – an ‘organic’ alternative?’. New
Scientist, 123 (1674), pp. 39-41.
Ellis, B.W., Bradley, F.M. and Atthowe, H. (Editors) (1996) The Organic Gardeners
Handbook of Natural Insect and Disease Control: A Complete Problem-Solving Guide
to Keeping Your Garden and Yard Healthy without Chemicals. United States of
America: Rodale Press, Inc.
Garden Organic (2013) Available at:
http://www.gardenorganic.org.uk/factsheets/pc20.php (Accessed: 16/05/2013)
Moss, S. (2006) The Garden Bird Handbook. London: New Holland Publishers (UK)
Ltd.
National Gardening Association (2013) Available at:
http://www.garden.org/ediblelandscaping/?page=201103-how-to
(Accessed: 16/05/2013)
PAN UK (2006) Available at: http://www.pan-uk.org/pestnews/Homepest/slugs.htm
(Accessed: 17/05/2013)
Piper, R. (2011) Pests: A Guide to the World‘s Most Maligned, Yet Misunderstood
Creatures. United States of America: ABC-CLIO, LLC.
RSPB (2013) Available at:
http://www.rspb.org.uk/wildlife/birdguide/name/s/songthrush/threats.aspx
(Accessed: 13/05/2013)
Soil Association (2013) Available at:
http://www.soilassociation.org/frequentlyaskedquestions/yourquestion/articleid/23
69/how-do-organic-farmers-control-slugs (Accessed: 13/05/2013)
The Wildlife Trusts (2009) Snail & Slug Control – Wildlife Friendly Control Methods.
Available at: http://www.wildaboutgardens.org.uk/resources/leaflets/SnailSlugControl.pdf