Organic Strategies for Slug and Snail Control
© Frances Michaels
Australia has 6,000 species of native snails, none of which cause problems to garden plants. Some of our
native species are carnivorous, feeding on garden snails.
The common brown snail Helix aspera
is an unwanted arrival from Europe. It can take from 4 months to
2 years to mature and may live 12 years. Snails are hermaphrodite and during the warmer months can lay several
egg clusters. The clusters contain up to 100 white eggs, at a soil depth of 20-40 mm.
Effective control of snails and slugs in the long term needs a combination of cultural, biological and
chemical methods rather than relying on a single solution.
Since all of our pest snails and slugs are introduced to Australia, the range of native biological controls is
limited. Predators include some birds, including magpies, kookaburras, mudlarks and starlings. The appetite
of birds for snails tends to vary greatly from area to area. Other predators include blue tongue lizards,
rats, centipedes, frogs, predatory beetles, predatory snails and slugs. Chickens or ducks, particularly Khaki
Campbell or Indian Runner, can provide effective, long-term control in orchards. Poultry are too destructive
in gardens to be given unlimited access but in small mobile cage systems rotated over garden beds, they will
clean up slugs and snails, fruit fly, 28-spotted ladybeetle and other pests that are attempting to hide out
in the garden.
Physical and Cultural Controls
Start with a garden cleanup to reduce snails and slugs breeding sites. Wear thick gloves and gumboots to
remove any old wooden boards and other garden rubbish. Check around the compost heap, inside stored pots and
around drains and retaining walls. Have ready a bucket of soapy water to drown any you find or a bucket of
just hot water if you keep poultry. Simply stepping on them may still allow mature eggs to hatch.
Handpicking, will over time, greatly reduce the number of snails; it is less effective for slugs. The best
time is 2 hours after sunset by torchlight. Consider offering a small financial incentive to young members
of the household to collect them.
Barriers can be used to protect vulnerable plants and young seedlings. Suitable materials include
diatomaceous earth, crushed eggshells, lime, wood ash, wood shavings and sawdust but these are only
effective when kept dry.
Tests in the USA have shown copper banding out-performed all other methods for protection from slugs and
snails. When the pest makes contact with the copper it causes a reaction similar to an electric shock,
which repels them. It is non-toxic, very long-lasting, with no possible potential poisoning of other
animals, pets or children.
Copper Barrier Tape is very
effective used as individual collars around young seedlings or pots. Worldwide research shows that copper,
a soil trace element, is also an excellent repellent for slugs and snails and will kill when sprayed
directly on them. Escar-Go
copper spray that creates an 'invisible' barrier when applied around plants, on tree trunks, pots or letter
boxes that lasts for months, doesn't wash off and is completely safe around kids, pets and wildlife.
Least Toxic Chemical Controls
Repellent sprays can be made at home from garlic or wormwood.
Eradicate Snail and Slug Bait
is based on iron. This product minimises the risk of harm to pets, poultry and wildlife and is
very effective when compared to the following baits. It has the added advantage of breaking down in 1 to 4
weeks to become a soil micronutrient.
Other snail baits containing either metaldehyde (green) or methiocarb (blue) have been around for many
years. Metaldehyde baits are preferable to methiocarb because they break down relatively quickly to form
acetic acid (vinegar) and are less toxic. Metaldehyde by itself is a snail and slug attractant but it is
usually mixed with wheatmeal and an added bitter substance to discourage pets and wildlife. Metaldehyde bait
is also produced as a dolomite pellet with no attraction for pets and wildlife. If using baits, place them in
a container to restrict access of pets and wildlife and to reduce leaching of chemicals into the soil. Use as
few pellets as possible, to prevent resistance to the chemicals increasing in the snail and slug population.
Don't use these baits at all if your poultry have access to the garden.
Homemade traps such as inverted grapefruit halves, pots or wooden boards can be placed close to where the
slugs and snails are harbouring. Check early each morning or they will become habitat instead! Beer, wine or
any yeast product mixed with water, is an attractant; place it in a bowl, with the rim 1 or 2 cm above the
ground, to drown them. Research has found sugar water (5% sugar solution) to be a highly effective slug
attractant. Empty the traps every day into the compost or chook run.
Eradicate Snail and Slug Bait
Slug and Snail Trap