Rat-killer extraordinaire

Gliricidia septum, a fast-growing leguminous tree widespread in the tropics, has as many names as it does uses: “mother of cacao,” because its branches shade cacao plantations, “quick-stand” because it's easily propagated from cuttings, and “Imperata destroyer” for its herbicidal properties.

But the name that should mean most to small farmers is “rat-killer.”

Because rats attack plants at every growth stage, they pose a constant danger especially for high-density crops like rice. Some 10 per cent of the Philippine's entire rice crop is destroyed by rats every year, and recent advances in rat control have concentrated on such high-income cash crops.

But small farmers need help too. Unable to pay for high-cost pesticides, equipment and advanced techniques, they're forced to use traditional methods, which are rarely applied systematically and are often proved unsuitable. A better answer could be the use of natural toxins, which can be produced locally and require neither a high outlay nor external financing.

Enter Gliricidia septum, whose leaves contain a substance called coumarin which, under the effects of the bacteria produced in fermentation, is converted into the anticoagulant diacoumerol. Anticoagulants are an efficient natural method of pest control because they reduce the protein prothrombin, a clotting agent secreted in the liver, and eventually cause death from internal bleeding. Tests have shown that while the toxin that Gliricidia produces does not act rapidly, repeated doses lead to fatal hemorrhaging within a few days.

Unlike many other poisons, anticoagulants do not produce bait shyness, which rodents tend to acquire as soon as the first victims of other poisons are taken. And Gliricidia has a number of other advantages. It's not toxic to humans-in fact, its seedlings are even considered a delicacy. It serves as an excellent feed for livestock. It can form living hedges, posts for yam growing, provide green manure and enrich alley culture in barriers for erosion control.

Gliricidia septum acts potently on insects as well as rodents. In many countries, its leaves are placed in chicken runs, or left to soak in hot water and used to eliminate fleas and lice on domestic animals. In a survey in the Philippines, 72 per cent of the farmers interviewed said they put Gliricidia branches in their rice fields to keep bugs and other pests away.

U.S. scientists conducted research on the toxic effects of Gliricidia on rodents in Central America and reported in the American bulletin Echo Development Notes on how it is used. They found both bark and leaves effective.

Farmers in Honduras, they said, prepare the poison by taking two large pieces of bark from the Gliricidia tree and boiling them in water with about 10 kilograms of wheat. They toss the wheat into the fields, where rats and mice that feed on it die within days. Mexican farmers grind the bark or leaves, then mix it with damp wheat or spread it on banana slices. In Panama, they grind the leaves, mix them with cereals and leave the concoction to ferment in the hot humid weather, because this activates conversion of coumarin into diacoumerol.

Noting that no one has yet provided a precise formula for the poison, and that documentation is lacking on many farmers' experiments, Echo Development Notes has asked readers to send their individual recipes, including details on how they prepare the poison, what ingredients they use to make bait attractive, and whether their preparations can be stored and marketed. Ceres readers who can provide information should write: Martin L. Price, Echo-Development Notes, 17430 Durance Road, North Fort Myers, Florida 33917, U.S.A.

Fay Banoun