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3 Oct 2014
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The War on Slugs - Listeners' Emails
We spoke to Dr Robert Hollingsworth about his research into caffeine being used to kill garden slugs. The study found that a 1-2% caffeine solution kills slugs and snails and concentrations as low as 0.01% were enough to put them off their food.

Bearing in mind that a cup of instant coffee contains about about 0.05% caffeine, and brewed coffee is generally stronger, here are a selection of emails we received from our listening gardeners.

The researchers involved in your programme, and those who have brought this to your attention, are obviously not aware that caffeine was patented for this use as long ago as 1984, as shown in the attached patent by James Nathanson, WO8601724, which discusses the likely biochemical reason for the effect (caffeine is a phosphodiesterase inhibitor). I note that the concentrations of caffeine required are high (~2%, as correctly reported on Today). This means that caffeine is about 100-1000 fold less potent than many modern pesticides and hence not an attractive commercial proposition. However, I don't suppose this will deter your listeners from giving it a try.
Dr Mike Turnbull, Syngenta.

Just tried the coffee remedy on the slug in our garden as he wiped his lips having devoured most of an iceberg leaf. He turned (with effort) to me and drawled: "Hey man, What is this? No mint?"
Sean Williams, Hertfordshire.

One saucer of beer placed in my garden catches and kills about thirty slugs a night....they are not very discerning, as lager seems to work just as well! I am told that milk works too, but have not yet tried it ...... so perhaps that left over cup of white coffee would be worth a go!! I sometimes find very tiny slugs queuing up trying to find an easy route into my saucer, these are easily helped with a cocktail stick.
Paul Rogers, Isle of Wight.

Slugs love bran but it kills them! I feed my garden birds with a plateful of porridge oats and bran each morning the birds eat the oats and at night all the slugs and snails have a feast on the bran. In the morning the birds eat all the dead slugs. A good bit of recycling?
Angela Morton.

Before encouraging people to rush out and sprinkle their gardens in strong coffee, I think you should re-assure us that this method it won't harm the earthworm, the gardener's friend! I prefer my own control method, which involves patrolling the garden twice daily, at dawn and dusk, armed with an old dinner plate, a shovel and a pair of stout shoes. Pick the snails up and deposit on the plate, and scoop up the slugs using the rim. Deposit your haul on a nearby path and stamp on it hard! Use the shovel to collect the debris. Foolproof, ecologically sound and the stamping bit is a good stress buster.
Ruth Durrell, Cheshire.

We have been emptying the coffee pot, grounds and all, onto the garden for 11 years. Although it acts as a great conditioner for our thin chalky soil, the slugs & snails seem to thrive on it. Sorry to disappoint
David Muddiman, Brighton.

Tried, it works! But could it be that pouring 90 degree black coffee on anything will kill it?
Richard Bushrod, Kent.

To save my runner beans from the ravages of the slugs and snails I put the coffee grounds from making fresh coffee around their stems. Unfortunately this seems to have had an adverse effect on them causing hyperactivity and insomnia, they also seem to have developed the shakes? Meanwhile the slugs and snails seem to be up all day now munching away, rather than just at night?"
Philip Tyler.

Well, that was a classic demonstration of the BBC's inability to report science, or perhaps the assumption that the audience is too dumb or uninterested to listen. You had an American scientist on the telephone, who presumably had been told the BBC wished to publicise his work. He had sprayed 2% solution of pure caffeine onto ... onto what? The soil or the foliage? He had found it removed molluscs. By direct killing or by aversion? All species? (Some slugs are carnivorous and helpful.) Did it affect slugs in the soil, or just on the surface? All good questions that might have been asked and would have been understood by the listeners to, say, Gardeners' Question Time. But no. The interviewer asked if pouring coffee over your garden would remove slugs, and persisted on this whimsical vein despite the discomfort of the interviewee. The story then occurred in the 8 o'clock news with Brian Perkins reporting that "a cup of coffee could wipe out the problem of slugs and snails" as solemnly as the BBC reported the death of the Queen Mother.

Will you now ask the Astronomer Royal's views on Wimbledon and identifying stars? "You cannot be Sirius!"
R. Allan Reese, Hull.

running out of time?
You can email Today with your comments or tips on controling slugs at or discuss this or other topics with other Today listeners on our message board.

I have just given a slug some coffee as suggested. It advanced, had a sip and then asked for some orange juice and a bit of croissant. The slugs clearly do not read the right research or listen to Today.
Malcolm Ridout, Oxford.
Like everyone else, we have had a slug and snail plague, no longer! Forget the pellets and poisons and strong coffee (what a waste!) For ten days I went out into the garden after dark, armed with wellington boots, rubber gloves and a torch and picked the pesky creatures off the plants and killed them, now I only go round about once a week just to keep them under control, our garden is blooming, even the beans are safe!
Liz Preece.
I always empty my coffee grounds onto the garden, it's the easiest way to dispose of them. Unfortunately the slugs appear to thrive on it, I've been overrun with them this year! The best way to ensure a slug free garden is to keep chickens and allow them to range freely, but as the hens will also eat the flowers, leaves and stalks of plants, then scratch up the roots, keen gardeners may not wish to pursue this!
Deborah Guest, Oare.
Jim is right to suggest the use of black coffee - slugs only like white and will soon disappear if none is available. In fact some slugs are so fussy, they will vanish unless a good selection of mints is on offer.
Rob Hudson, Kirkby-in-Ashfield.
It works. I have just left a cafetiere of my favourite breakfast coffee on the patio in front of two prize slugs and they have completely ignored it. On the other hand, they are tucking in to the orange juice, croissants and honey which my research shows are not effective deterrents.
Andrew McCabe.
You are very wrong to help to promote an unapproved slug killer - caffeine or coffee. This is a totally illegal, under EU regulations.
David Delaney.

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