How to control slugs
Slugs
and snails are tolerated by very few gardeners, and though they have
many natural predators, like toads and thrushes, these rarely seem to do
a good enough job, so we need to intervene to protect seedlings and
young plants. The main species that cause us problems are the field slug
Deroceras reticulatum which is light grey to fawn, the garden
slug Arion hortensis which is dark grey to black, and the
keeled slug Milax spp. which is grey, brown or black with a
distinctive ridge along the back. The keeled slug lives mainly under the
soil and is the one that ruins your potatoes.
We have tried some of the traditional ‘barriers’ like crushed egg
shells, hair and soot and have found them to be largely ineffective.
Slug traps can significantly reduce the number of slugs in an area, and
we would like to recommend the
‘Slug X’ trap which catches lots of slugs
but not beetles, unlike some of the home made yoghurt pot types. All
these traps are best baited with beer, preferably ale, which the slugs
are attracted to and drown in; at least they die happy!
Protecting plants in containers
Over several years in the ASK Organic Garden, we have tested ways of protecting susceptible container grown plants, like hostas, lettuces and violas, from the ravages of these slugs. With the exception of 2006, when a combination of very dry conditions and a resident hedgehog produced hardly any results, we have been able to draw some conclusions about the effectiveness of different barriers.
Adhesive Copper Tape -Slugs are known to suffer the equivalent to a mild electric shock when coming in contact with copper, so they simply will not cross this kind of barrier. It is very important with this tape to make sure leaves don’t hang over the barrier as this gives the slugs a bridge to cross to the plant.
SAS Slug and Snail Repellent - This contains a natural yucca extract which is sprayed onto the plant to make it unpalatable to slugs and snails. We have found it does repel slugs and does not damage even delicate plants like French Beans. It is best used under cover as it is expensive and needs renewing after rain.
Coffee grounds - Recent research has shown that caffeine can damage slugs. We have used spent coffee grounds, but the caffeine in instant coffee is also reputed to work. Slugs coming in contact with caffeine have been seen to “froth”. It does need to be renewed regularly and after heavy rain. Our experience is that it is only partially effective – but it’s free!
Aquashell - This product has recently been introduced and is marketed as a slug and snail deterrent. The shell, a by-product of the shellfish industry, has been steam cleaned. We had reservations about this method which relies on the roughness of the shell like traditional deterrents such as egg shell and spruce needles and, indeed, it gave only moderate protection.
Slug Stoppa Granules - These are completely safe for pets, wildlife, children and, indeed, slugs. They are supposed to suck the slime from any slug that tries to cross them and should not need replacing after rain. We found these granules gave almost no proteciton.
Slug Defence Gel - The gel behaves in an interesting way: it expands to form a barrier in wet, slug-friendly conditions, and contracts and nearly dries out during hot, dry conditions.
Wood Ash – a thick layer gives some protection from slugs, but can damage young seedlings and even established plants.
Controlling slugs and snails in the soil
1. Dig over the soil. Exposed slug eggs will dessicate and be eaten by
visiting birds.
2. Remove mulches in late autumn, this is where slugs will shelter.
3. Keeled slugs - the ones that attack potatoes and other tubers - can
best be controlled through regular digging.
4. Slugs feed on decaying organic material. Deny slugs food and shelter
by keeping the garden tidy.
5. Apply the biological control Nemaslug. Millions of nematodes are sold
in each pack. This is dissolved in a can and watered onto badly affected
areas to give you six weeks protection from slugs. Remembering that the
large black and leopard skinned slugs eat mostly dead vegetation, and
will eat other slugs, so cause little damage to our plants.