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Caffeine May Evict Garden Pests

Repels slugs and snails, and it's safe

THURSDAY, June 27, 2002 (HealthDayNews) -- If snails and slugs are ruining your plants but you're loathe to use pesticides, a new study says you may someday kick them out with what gives you a kick in the morning.

Caffeine effectively repels slugs and snails from ornamental plants, some preliminary studies by the U.S. Department of Agriculture (USDA) suggest.

It's way too early to advise home gardeners to pour a little java on their flower and vegetable gardens, emphasizes Robert G. Hollingsworth, one of the government researchers who details the finding in today's issue of Nature.

However, it's conceivable that a commercial firm will take the research and run with it to eventually produce a natural caffeine pesticide. "The hope is since this is a natural product, some company will pick it up," Hollingsworth says.

Hollingsworth's team, based in Hawaii, began by testing caffeine sprays against a frog that infests potted plants in Hawaii. That's when they noticed that a 1 percent to 2 percent caffeine solution killed slugs and snails, and concentrations as low as 0.01 percent deterred the pests from feeding. (In comparison, instant coffee has about 0.05 percent caffeine, brewed coffee more.)

"The lowest levels we saw an effect was at 0.01 percent," Hollingsworth says. At this level, he says, there was a decrease in feeding, but the caffeine did not kill the pests.

"We saw a 25 percent decrease in feeding at less than the strength of coffee," Hollingsworth adds. "At even less than 0.1 percent, there was a change in feeding behavior."

Among their tests to evaluate java as a pesticide, they dipped leaves of cabbage in caffeine solution, dried them, and let the slugs have access. They treated snails topically with caffeine solution in the lab, and then evaluated their heart rates. And they conducted actual greenhouse tests to see if caffeine could keep the pests away from potted orchids.

The java pesticide isn't perfect. "There was some damage to tender leaves," says Hollingsworth, a research biologist. "There was some leaf yellowing." Even so, he says caffeine has potential to save ornamental plants such as orchids.

Exactly how does the caffeine work? "We didn't study that," Hollingsworth says. Other studies done in tissue culture samples suggest the caffeine affects the neurons of the pests, he adds.

Coffee grounds are often recommended on gardening Web sites as a good way to rid the garden of snails and slugs. "Coffee grounds would have a lot of other things, including acid," Hollingsworth says. "If it works, it may not work for the same reasons [as the caffeine pesticide they tested]."

Caffeine is a natural product and classified by the U.S. Food and Drug Administration as a GRAS (generally recognized as safe) compound.

The USDA research is a applauded by experts at the Pesticide Action Network North America.

The study looks "very interesting," says Margaret Reeves, staff scientist at the San Francisco-based organization, which promotes the use of natural pesticides. "It's a great concept. We are always looking for environmentally safe alternatives to hazardous and toxic pesticides, and this looks like a very promising solution."

"It's an excellent alternative that should be explored," says Pamela Laurence, a spokeswoman for Pesticide Action. "Caffeine as an active ingredient is not bioactive, is not volatile, and is a naturally occurring compound. This is a viable alternative."

What To Do

For more information on pesticides, see the Pesticide Action Network or the Environmental Protection Agency.

SOURCES: Robert G. Hollingsworth, Ph.D., research biologist, Agricultural Research Service, U.S. Department of Agriculture, Hilo, Hawaii; Margaret Reeves, Ph.D., staff scientist, Pesticide Action Network North America, San Francisco; Pamela Laurence, spokeswoman, Pesticide Action Network North America; June 27, 2002, Nature
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