Sunday, 10 January 2016

Slug control. More about molluscs

Are gastropods really so ghastly?
I will frequently state ‘slugs’ when I mean slugs and snails

My first opus on slugs and snails was posted two years ago and very few read it. In contrast every time I talk to gardening groups everyone asks about them. I wonder where I go wrong. Perhaps there is so much rubbish out there that my own slippery contribution is google linked on an exceedingly high page. 

Slugs and snails are the only molluscs that have emerged from the water to live on land. Slugs and snails love wet conditions! If drainage is poor and it is a wet season they will give gardeners a problem.
Not only do slugs thrive when it is wet, control measures that use metaldehyde based slug pellets often fail at that time. Not only is the dose of poison less likely to kill them but pellets when wet are much less attractive.

Slugs love organic matter but that is no reason to remove it
There has been an awful lot of organic matter on the surface of my vegetable garden this Winter with debris from cleaning my ponds (It will be redistributed in Spring)
How ever often gardeners read about the horticultural benefits of organic matter they still remove it in the misplaced interest of hygiene and tidiness. The latter I can understand although I don’t share this quality. Compost and manure are deemed desirable but not dead weeds, leaves and other debris. 
I always complain that when nature offers to add organic matter to the garden that tidy fusspots spurn it. Some gardeners even feel guilty if they hide a dead hand-pulled weed behind a tall plant. I do not bother to disguise mine expecting them to quickly shrivel and benefit the soil. 

Quelle horreur, organic debris might even attract slugs. This might be so, but what could be better than them acting as nature intended. Let them rasp away any dead vegetation and start the first stage of natural organic decay. Better eat this than your plants. And they prefer it.

Look at slugs differently 
You will always have slugs and snails. Their rate of procreation is little effected by lots of debris. There are other significant influences on their rate of breeding including  a gardener’s diligent destruction. The quicker you kill those species whose fecundity is effected by the number of slime trails they crawl over the more they will breed. 
Slugs can travel considerable distances to come to your garden. If they find it surgically clean of plant debris they are so much more likely to eat the leaves of your plants. 

Big black one

Do minimum cultivation methods minimise slug and snail damage?
I personally think so and the more I read I find others agree. The closer a soil is to nature the greater the likelihood of natural control. For example there will be more hungry black shiny highly mobile ground  beetles to devour slugs and snails. It is ironic that so many gardeners inadvertently drown ground beetles in childish slug pubs!
There is more slug damage to seedlings in loose fluffy seed beds. Farmers are advised to make firm seedbeds and avoid lumpy clods. Deep sowing apparently helps minimise slug damage to seedlings and agricultural advisors  frequently recommend deep firm sowing to growers of grain.
I will explore the theme that there will be less slugs with minimum cultivation in a future post.
They come in all colours

Use of slug pellets
This is the normal control used by farmers and growers whose produce would never sell if there was even a hint of slug damage. Slugs in a lettuce might ruin a reputation. In the middle of a cabbage slugs don’t endear you to your culinary cutie.

Gardener’s worry pellets are a problem to wild life. If used sparingly and responsibly and in limited circumstances I don’t really think so. The real danger of their poison is that domestic animals might ingest a quantity from an unprotected packet. There have been several tragedies. I personally remember with sadness a doctor whose dog died after devouring a pot full left in her greenhouse.

Slug pellets are a bran bait charged with poisonous metaldehyde. They also contain a chemical that makes them highly unpalatable to animals and birds. The bait attracts slugs and it acts over several centimetres. In my opinion no more than half a dozen pellets per square meter are needed. I deplore gardeners who apply pellets enough to create a blue mulch. That is how real harm is done. Rates of application of pellets on a farm will be no more than about four kilograms of pellets, (not raw metaldehyde) per hectare. That’s far sparser than the quantity applied by the ignorant and ecologically uncaring.
Four kilogram per hectare per hectare is four gram per ten square metres.
Why that means with my gardener’s arithmetic that an ounce of pellets would cover eighty square yards!
I have six acres of garden and one small pot of slug pellets last me over two years. Most of my gardens receive no slug control whatsoever!

My own Yaramila fertiliser is a blue prill and I sometimes imagine visitors think I have been scattering slug pellets! Even my fertiliser is spread much more thinly than some idiots slather on pellets.
I secretly suspect that the irritant action of my highly soluble fertiliser in the vicinity of a newly planted cabbage might be a slight slug deterrent but unfortunately not after it has rained.

Gardeners forget that pellets are a bait and sometimes apply them close to their plants. The incoming slugs or snails are very likely to prefer lettuce to the bran. Spread pellets widely over the whole patch of any new planting in your vegetable garden and then go a little wider. Best to attract the slugs away. If I suspect my newly planted sweet corn might be vulnerable, I spread a few pellets the day before planting. (On the rare occasions I remember to spread any at all!)
It is sometimes possible to cover your slug pellets. Not only does it keep them dry it might hide them from birds. Unfortunately dead poisoned slugs are toxic too. 

A couple of grey ones
I sometimes get slugs in my greenhouse and occasionally use slug pellets. Only on the bench if as usual there is a frog on the ground! Frogs from my ponds love the plant nursery outside my greenhouse and often migrate inside through its crumbling wall.

Remember too that slug pellets under a plant canopy such as ground covering hostas will be hid from the birds.

Snails have made a real mess of Steven’s yucca. If the odd slug pellet lodged in the leaves it might help
I once visited a famous garden in Seattle. Our guide casually stated that they did their annual slug kill in March. Whatever did he mean?  No gardener challenged him. I imagine they thinly spread slug pellets all over the garden. Just like a farmer covering the whole of his field. I imagine such a cover is quite effective as slugs and snails travel more than you  imagine.
In my opinion the ornamental perennial garden needs no treatment at all -  except for the hostas.... and perhaps the delphiniums not to mention the….

I read that the organic establishment in ‘force majeur’ situations sometimes gives a special licence to their members to use slug pellets based on iron phosphate. Having read this article I think they might be misguided. As the author states ‘alternative medicines’ often escape proper safety controls.

How damaging can slugs be in the garden?
There are two types of gardener. Those who take slugs in their stride and marginally adjust their methods to accommodate them. Others become neurotic and despair when they are insulted by even the slightest scar. They go out at night with torches and salt and buy geeky products.They spend a small fortune on biological control. Just for a few carrots!

When cutting back my hellebore in December I found these snails. I did not have the heart to kill them and they remained there a couple of days before they slithered away.

Most plants are hardly effected by slugs at all. There are however some circumstances where plants are very susceptible and damage may be severe.
Often the problems are associated with the production of vegetables and plants such as strawberries. Damage might be severe where soft plants are raised inside and planted outside. Damage might be  be particularly nasty if the weather is wet and cold and plant establishment is slow. Plants that are in any way stressed and wilted, often newly planted, attract slugs. Perhaps the nearer to death the more slug friendly your plants are.

Dare I call this a slug club? The snails take a break in Summer, especially when it is dry and hibernate in Winter. My pile of bricks (used to anchor and build up walls for my fleece) is always fully booked.

What else can I do?
Many species of slugs and snails do not feed on garden plants at all. They browse on algae and fungal green slime and eat decaying vegetation.  Don’t waste your time killing these kinds. Heed the old country saying
If it is black put it back
If it is grey, keep it at bay
Unfortunately that does not apply to those black slugs eating your potatoes!

So here are a few tips...
Encourage birds
Encourage frogs, have a garden pond 
Traditional East Yorkshire gardeners kept a toad in their greenhouse
Hedgehogs can eat 500 slugs in a night
Sometimes susceptible crops such as potatoes have more resistant varieties.
Use avoidance strategies such as early lifting of root crops
Plant sacrifice plants as a decoy for slugs
Listen to Mr Foolhilly….

I believe that slug 'problems' are of our own making and stem from a seriously distorted perspective of 'what a garden should look like'. Orderly rows, clean soil and immaculately manicured lawns and hedgerows are so alien to nature that we create terrible distortions of balance - that all too critical component of nature’s stability. This is often compounded by our overpopulation with the consequence that a 'garden' can often be as tiny as a container or two. In such tiny portions, nature finds it near impossible to establish any sense of balance.

When I took over my field, it had been used extensively as agricultural smallholding for many decades. I planted a third of it with wheat (for the chickens). It was a wet year and every ear was smothered with small grey keel slugs. My first stab at re-establishing a sense of balance came with the release of half a dozen Khaki Campbells. For weeks, their crops were gorged with a rich diet of slug protein. For the ducks to harvest the slugs, they had to be able to be active by first light, so they were left un-cooped - the local foxes soon dined well on recycled slug…

Read the rest of Fool’s comment in my previous post about slugs and snails



  1. Hi Roger, as usual I agree with pretty much everything you say on the subject, I too leave leaves and debris on the borders to return to the soil and even though I have a predominantly very wet garden, it was just damp until this winter, I don't think this practice adds to the slug problem. I was particularly interested to read about the "slug kill" in Seattle because I do exactly the same thing, at the first signs of a rise in temperature, usually March, I spread pellets thinly in the areas which I would most expect slugs to congregate over winter and more importantly where they are likely to have laid their eggs. The theory being to catch the "first hatching" therefore reducing the number of slugs able to breed that year. A couple more scatterings in the areas where there are vulnerable plants during the year keeps things under control. Although I appreciate that pellets are bait I still prefer to concentrate on areas which I think are more likely to appeal to the little perishers!

    1. A helpful contribution as ever Rick. I agree with your strategy of selecting vulnerable areas. My point for the benefit of less experienced gardeners than yourself is that little piles of pellets surrounding a precious plant is the wrong thing to do

  2. I used a spray called Grazers slug and snail control on my hostas which is supposed to make the leaves unpalatable and seems to work. It requires a regular spraying regime. Obviously they have to have a little nibble ti find out they don't like it but our hostas kept most leave intact. Another thing that seems to work is to place pots in a saucer of water to create a moat. That works as long as the leaves of the plant are not accessible using other routes such as a wall or neighbouring plants. The saucer needs to be kept topped up and pots can be raised a little if the plant would suffer from sitting in water but hostas don't seem to mind.

    If a slug has nibbled a strawberry I find that if it is left on the plant the slug will return to the same fruit rather than moving on to another as they will do if the nibbled fruit is removed.

    1. A few helpful tips Sue. Our mutual blogger friend Alain recently posted about traditional Italian plant water collecting saucers which had a central platform so plant roots were not in the water.
      I have noticed the same as you have on the strawberries. The same principle seems to work when wasps or birds eat fruit

    2. I saw Alain's photo and commented that it would make a good slug moat.

    3. All information gets recycled Sue. And there I was pretending to be original!

  3. Very interesting and useful. I can see from the pictures that your slugs and snails are different from ours, even if they have the same effect. I use some pellets but the best method here is to go deal with them during a rain after a dry period. I also have a few boards which I turn to kill them. I am always careful not to remove the bodies as I noticed they cannibalize each other. You kill one and a few hours later you can kill 3 or 4 more that are eating the dead one!

    1. Your boards will act as a lure for them as do my little stacks of bricks Alain- sounds to be a useful method. You will have noticed that some of my slug pictures are on bricks! Also not pictured are the beneficial beetles and centipedes they attract. Not to mention woodlice! I gave my robin a treat yesterday when I turned a few!
      In general I do not fuss myself when the residents of the heap are disturbed when I use the bricks. I have no idea whether they increase or decrease the slug damage on my cabbage. Any more than the log pile beetle habitat left as a 'feature' on the village plot

  4. I have always been reluctant to use blue slug pellets after several cows on a neighbouring farm died after gaining access during the night to a store with slug pellets. I have been using the Iron Sulpahate Organic approved form with a clear conscience until I read your article!
    What are you views on the liquid form, to use on say hostas?

    1. Sorry to hear of another tragedy, Brian, but again with the concentrate rather than actual application
      I think you mean iron phosphate and as I am a great believer in all the benefits of iron sulphate to achieve 'a perfect lawn', please excuse my exaggeration Brian, I think I would have heard of it.
      I was very impressed with the link debunking iron phosphate based pellets.
      I have no experience of liquid formulations of metaldehyde but would imagine dangers of accidents from stored product is the same and I am dubious of solutions of metaldehyde being applied to soil.

    2. Sorry Roger I should of checked my facts before I replied instead of relying on memory!! I presume you use iron sulphate as a moss killer.



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