Page 24 - ALG Issue 3 2014

Feature on...
Know your slugs
I don’t understand why slugs have such romantic names! There’s the Orange Banded Arion, the Dusky slug and the Chestnut slug - they almost sound friendly, although the invasive Spanish Stealth slug has a much more appropriate name. Along with snails I think they must be the creatures that cause allotment gardeners the most despair and loss of crops and money.
According to the Slugwatch website http://www.slugwatch.co.uk/
“There are approximately
30 species of slug in the UK
matting impregnated with copper salts; the copper emits a tiny electric charge that repels the pests.
Plastic barriers such as drink bottles with the top and bottom cut off inserted in to the
Controlled environment
Grow vulnerable seedlings on in a controlled environment like a greenhouse until they are strong enough to withstand an attack by slugs.
Encouraging predators
Frogs, toads and slow worms are all partial to slugs, as are ground beetles and creating suitable habitats on your plot will encourage them to stick around. A small pond will entice a frog population; toads and slow worms like a drier atmosphere such as the compost heap or pile of stones. Beetles will congregate under wooden boards or slates, which will also attract slugs but if checked regularly the slugs and their eggs can be removed.
Growing resistant varieties
There are certain varieties of vegetables that are more slug resistant than others. The
and four of these, the netted or grey field slug, the garden slug, the keeled slug and the large black slug, cause approximately £8 million in damage to vegetable crops each year. On average a
On average a UK garden is home to over 20,000 slugs
soil around young plants such as brassicas will give some protection.
Biological control
An application
of the nematode (Phasmarhabditis hermaphrodita) applied to moist but well drained soils that are at least 5°C,
UK garden is home to over
20,000 slugs and it is estimated that an acre of farmland can support over 250,000 slugs”.
Britain is the slug capital of the world. Our cool, damp summers and mild wet winters allow them to thrive, although
frost will kill off a percentage and they will withdraw underground in hot, dry periods. Their flexible, streamlined shape allows them to move through the soil and they are hermaphrodites. Each slug can lay up to 500 eggs per season in soil cavities, under stones or the black plastic on your plot; some are self-fertile but most will mate.
Slugs do have a part to play in the ecosystem; they break down vegetation
– in fact some slugs such as the leopard slug eat other slugs, along with rotten vegetation that they then excrete to fertilise the soil. Slugs are also a food source for toads, birds, beetles and mammals such as hedgehogs, badgers and foxes.
Slug Control
Barriers
Mulches such as sand, woodchip, eggshells or ashes can be used around susceptible crops to deter slugs; these can be useful whilst the plants are young and vulnerable but will need maintenance to keep them in place. There are also off the shelf moisture absorbent minerals that can be placed around plants to create slug barriers; there are even pellets based on wool that create an irritating woollen mat around the plant.
Plants in plots can be protected with copper slug barrier tape or stood on
at the start and the end of the season will infect the slugs with bacteria that cause
a fatal disease. Most slugs and certainly juvenile slugs are active below the surface, so the nematode is very effective at stopping a slug problem from developing. Large slugs, above about 8cm, are less vulnerable to the product.
Chemical
If you do use any type of
slug pellets it is important
that you use them properly
but the metaldehyde pellets
are particularly poisonous
to wildlife, pets and young
children. Metaldehyde
residues have also been
found in water courses due
to run-off from farmers’
fields. Pellets based on ferric phosphate are much less hazardous and are certified for organic use. A Which study in 2011 found that the organic pellets worked as well as the metaldehyde with the added bonus that the slugs crawl away to die.
The European Union has voted to ban the use of methiocarb slug pellets. They are mainly used by farmers, due to their hazardous effect on grain-eating farm birds such as finches and sparrows and after August this year they are likely to be withdrawn from sale in the UK.
Pellets need to be scattered thinly and evenly around the crops, at a rate of about 1 pellet every 10cm and may need to be replaced after rain, although slug bait needs to be placed on moist soil to work.
Pentland potato varieties have a high resistance, whereas the Maris Piper
is low but no potato is immune to keel slug attack. Spring cabbage, kale and sprouting broccoli have greater resistance than the sweeter summer cabbage, cauliflower and Brussels sprouts.
Hand removal
Wandering around the plot at dusk with a torch and removing by hand is also an option and after a downpour there will be hundreds of slugs around to harvest.
Reduce slug habitats
Weeds provide food for slugs and, along with patches of rubbish and long grass, places for them to hide so a tidy patch will help to keep numbers down.
Rotovation
It is possible to reduce slug numbers in your soil by about a third if you rotovate just as the weather is warming up and they are near the surface; this will also expose the slug eggs in the soil to predators and the weather. Digging by hand will also have an effect on slug numbers but to a lesser extent.
Traps
Containers sunk into the soil and filled with beer or milk will trap slugs; the rim needs to be 1-2 cms above the surface to prevent drowning ground-beetles (who are slug predators). There are also commercial products available.
Most plants, once established, will generally tolerate slug damage and control measures can be discontinued.
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Slugwatch was set up in 2012 by scientists at the John Innes centre, with the support of BBSRC and the Nuffield Foundation, to monitor the progress of the invasive Spanish slug. Although there have only been sightings of the species in East Anglia so far, there are fears that they will hybridise with hardy British slugs combining the worst of the Spanish slug with native tolerance to frosts and cold and become an even greater menace. Slugwatch are calling on gardeners across the UK to report sightings of this slug to Slugwatch via their webpage; the Spanish Slug varies in colour from between bright orange and reddish brown and can grow to a size between 8cm and 15cm when they have reached maturity – there are illustrations on the Slugwatch website.
If you do use any type of slug pellets it is important that you use them properly