Coffee is a wake-up call for slugs and snails, say researchers.
The United States Department of Agriculture Research Service in Hawaii has found that caffeine sprayed on plants or scattered around the garden as granules is a powerful deterrent.
The researchers, cited on the scientific journal Nature's website, reportedsnails coming in contact with the 1-2 per cent caffeine solution developed weak and irregular heartbeats. Slugs experienced "unco-ordinated writhing" before dying.
Dr Robert Fishe, of the International Pacific College, says the research means gardeners may soon be able to forgo damaging pesticides in favour of coffee, an organic weapon.
He recommends applying the coffee with a sprayer or scattering granules in problem areas.
According to Nature, most commercial slug and snail repellents contain harmful ingredients such as metaldehyde or methiocarb.
Coffee also contains metaldehyde, but it is considered to be at safe levels.
The Coffee Lab Roasting Company, in Auckland, had already heard of the pest-control method.
"When you make an espresso, you get a little pat that you can't use. It's spent ground coffee - chuck that on your garden," said one staff member.
But toxicologist Peter Usherwood, of England's Nottingham University, had some concerns.
"It's likely to have an effect on beneficial insects," he told Nature.
DoC researcher Dr Ian Stringer, who works with the endangered native snail, Powelliphanta, said residual caffeine in the environment was unlikely to harm the large snails, which reside in the Te Paki area near Cape Reinga.
Animal Action spokesman Michael Wise says the group recommends a garlic, saltwater and cayenne pepper mixture, which deters garden pests rather than killing them.
