Coffee breaks slug

Most gardeners have a favourite method of repelling slugs - some swear by a jar of beer in the flower bed, others sprinkle them with salt. Now an even deadlier weapon can be added to the armoury: coffee.

Scientists have discovered that caffeine could be the perfect, environmentallyfriendly answer to keeping the pests at bay. Research in the United States has shown that the stimulant is lethal to slugs, even at concentrations lower than a weak cup of coffee.

The findings, by the US Department of Agriculture (USDA), will be warmly welcomed by gardeners who care for the environment. Unlike slug pellets, which contain highly toxic metaldehyde or methiocarb, caffeine is unlikely to affect birds, insects and pets.

However, the impact of caffeine on plants is still being studied. Trials show that coffee does not harm plants such as palms and orchids but could cause yellowing in ferns and lettuce.

Researchers stumbled across the slug-repellent properties of caffeine by chance, when they were field-testing caffeine as a potential means of controlling frogs. They noticed that large slugs and snails were dying in the area where it was sprayed.

The USDA team, led by Professor Robert Hollingsworth, then tested caffeine as a slug repellent by allowing slugs to bury themselves in soil, before dampening the soil with a water solution containing two per cent caffeine. After three and a half hours, 75 per cent of the slugs had fled.