AGRITRENDS: Botanical pesticides against pests and diseases

While modern agriculture produces high yields, more often than not, it is not sustainable. Expensive seeds and farm chemicals eat into profit while pesticides upset the natural balance between predators and pests, and chemical poison groundwater and rivers.

“Every year, hundreds of thousands of people are killed due to accidental poisoning by agricultural chemicals,” says Roy C. Alimoane, director of the Davao-based Mindanao Baptist Rural Life Center (MBRLC) Foundation, Inc. People who consume chemical-laced vegetables risk their lives since chemicals are not always dissipated, says Alimoane. Generally, chemicals accumulate in the human body.

The Geneva-based World Health Organization reports three people are poisoned by pesticides every minute around the world. All in all, about 10,000 die annually because of pesticides. Reports show that 62% of pesticides sold in the Philippines are insecticides. Of these, 46% are applied to rice and 20% to vegetables. Insecticides had become one of the major expenses of farmers that account for about 40% of total production cost.

The lack of regulation in most developing countries, including the Philippines, often accounts for the importation of banned pesticides. In 1992, the illegal use of cyanide compounds by cabbage farmers in the Cordillera region provoked a public outcry.

But Filipino farmers can actually do away with imported inorganic chemicals by using environment-friendly botanical pesticides. These are derived from plants which have been proven to have insecticidal properties.

“The increasing awareness of the dangers posed by chemical pesticides to human health is prompting many Filipino farmers to use botanical formulations that they themselves are preparing,” said a paper written by L. Masana and A. Manuel.

Eric Vinje agrees. In an article which appeared in Planet Natural, he writes: “Natural pest controls like the botanicals are safer to the user and the environment because they break down into harmless compounds within hours or days in the presence of sunlight. They are also very close chemically to those plants from which they are derived, so they are easily decomposed by a variety of microbes common in most soils.”

Previously, botanical pesticides were used widely until the 1940’s. These natural pesticides were displaced by modern synthetic pesticides that at the time seemed cheaper, easier and longer lasting.

“Botanical pesticides are one answer to the pest problem in developing countries,” says Gaby Stoll, a German agrobiologist and author of Natural Crop Protection. Stoll says the move from chemical to botanical pesticides is, “an important step in the search for a balanced, self-regulating agricultural system.”

One advantage of botanical products is that they are not very persistent. Most of them will break down quickly under influence of high temperature or sunshine. As such, they don’t have a long-lasting contaminating effect on the environment.

But the only hitch is that botanical products are generally not specific. In addition, many plant extracts will also kill or repel beneficial insects. It means to say that some botanicals are not risk-free. “Some are as dangerous as chemical pesticides,” Stoll reminds.

Just like synthetic pesticides, the botanical products should be used carefully. If a farmer decides, after a thorough consideration, that active control of a pest is required, botanical extracts are usually a better choice than chemical pesticides.

Tubli

In recent years, Filipino scientists have found many plants to have insecticidal properties. One of them is “tibanglan,” known locally in Mindanao as “tubli.” Government forest researchers found it to be highly effective against lepidopterous and coleopeterous insects.

The test conducted by the Laguna-based Ecosystems Research and Development Bureau included leaf rollers and fruit worm of okra, stem borers of eggplant, white aphids, corn weevil and larvae or tussock moth. Result of the study showed that 50%, 25% and 10% of “tubli” sap in water can kill samples in 20, 45, and 120 minutes, respectively.

“Tubli” has an ancient reputation as botanical pesticide. Ethnic groups in some parts of the country have long been using “tubli” as fish poison. In Brazil, people use it to eliminate the deadly piranha.

The insecticidal properties of “tubli” were first discovered in 1848 when the plant was first used against the nutmeg caterpillar. In 1940, the United States was importing 2,700 metric tons of “tubli” roots from Southeast to formulate pesticides.

Agricultural experts say “tubli” is very effective against aphids, beetles, borers, the diamond back moth, fruitflies, thrips, cabbage worms, fleas, flea beetles, lice, loopers, mites, mosquitoes, psyllids and slugs.

Kakawate

“Kakawate” or “madre de cacao” is so common that no one seems to pay attention to it. But the UN Food and Agriculture Organization (FAO) said that its leaves contain coumarin, which can be converted into an anticoagulant “discoumerol” found to be an efficient rat killer.

“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,” the FAO noted.

Tests have shown that while the toxin produced by “kakawate” 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,” the United Nations agency said.

In Science City of Muñoz, organic rice reportedly farmers spray their crops with fermented leaves and twigs of “kakawate” and neem trees to control pests and diseases. Some farmers find it convenient and effective, too, to just allow the “kakawate” leaves to drift to their farm when they irrigate.

In Baguio, a botanical pesticide prepared from kakawate leaves and other herbals are used to kill worms that attack cabbage and broccoli like cabbage butterflies, diamondback moths, leafminers, and inchworms.

In Ilocos region, a study made by the Mariano Marcos State University found that kakawate leaves are effective in controlling diseases that attack garlic like purple blotch and bulb rot.

Tobacco

“One of the best ways to eradicate the insects is by using tobacco spray,” said Serapion Madera, a farmer in Bansalan, Davao del Sur. Here’s what he did. He boiled 250 grams of dried tobacco leaves and stems in four liters of water for 20 minutes. After that, he allowed the water to cool and then filtered it through layered cotton cloth. He added four more liters of water to the solution and 50 grams of bar soap. He then poured the solution into corn funnels to kill stalk borer.

Madera had undergone training at the Mindanao Baptist Rural Life Center, a non-government organization. The MBRLC technicians said the tobacco solution can also be applied as a soil drench around plants to kill cutworms. It can be used to spray beans to prevent rust disease and also to control aphids, beetles, cabbage worms, caterpillars, grain weevils, leaf miners, mites, stem borers and thrips.

The tobacco solution, MBRLC technicians claimed, is especially effective against biting or sucking insects. When applied weekly with a brush, it is effective against ticks and fleas in cattle.

The Educational Concerns for Hunger Organization (ECHO) has developed another kind of tobacco spray. One kilogram of crushed or bruised tobacco stalks and leaves are soaked in 15 liters of water for 24 hours. The solution is then filtered; and three to five tablespoons of liquid soap is added. It is sprayed immediately to plants.

“Use tobacco sprays in the evening to allow them to work in the night,” the Florida-based ECHO reminds. “And in general, do not spray potatoes, peppers, tomatoes, eggplant or any plant in the Solanaceae family in order to prevent the spread of viruses.”

Another warning: “Do not let people or animals drink the solution, and when spraying, wear protective clothing – especially a mask, or apply solutions with a watering can only. Do not eat vegetables within four days of application and wash them carefully when you do.”

Tobacco is also no match against golden apple snail. To get rid of the pesky snails, finely chopped tobacco wastes can be strewn over the rice paddies a day after the rice seedlings are transplanted.

Credited for discovering the technique was Merlita James of the National Tobacco Administration’s research center based in Batac, Ilocos Norte. She said that 200 kilograms of finely chopped dried tobacco wastes is sufficient to destroy snails infesting a one-hectare area.

Aside from botanical pesticides, a farmer can resort to other means of pest control, according to Alimoane. These include tilling (which exposes pests that live in the soil and increases soil aeration), crop rotation (it stops the build-up of microorganisms around plant roots), crop combination, and companion planting.

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