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Botanical Pesticides Gain Wider Acceptance

Modern agriculture produces high yields, but is often not sustainable. Expensive seeds and farm chemicals eat into profit. 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.

The Geneva-based World Health Organization reports that three people are poisoned by pesticides every minute around the world. All in all, about 10,000 die annually due to pesticides.

Reports said that 62 percent of pesticides sold in the Philippines are insecticides. Of these, 46 percent are applied to rice and 20 percent to vegetables. Insecticides had become one of the major expenses of farmers that account for about 40 percent of total production cost.

According to Alimoane, people who are eating chemical-laced vegetables are risking their lives since chemicals are not always dissipated. Generally, chemicals are accumulated in the human body.

The lack of regulation in most developing countries often accounts for the importation of banned pesticides. In some instances, farmers try to apply untested chemicals which they think could drive away insects and pest. In 1992, the illegal use of cyanide compounds by cabbage fanners in the Cordillera region provoked a public outcry.

In time, the use of botanical pesticides again gains wider acceptance among farmers. Botanical pesticides are derived from plants which have been shown to have insecticidal properties. Used widely until the 1940s, these natural pesticides were displaced by modern synthetic pesticides that at that time seemed cheaper, easier, and longer lasting.

“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.

“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,” wrote Eric Vinje of Planet Natural. “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.”

Many plants have insecticidal properties. Extracts of these plants can be sprayed on the crop to either kill or repel insects. Take the case of atis, which is best used against aphids, ants, and other crawling insects. The seed of the fruit is crushed and mixed with water. The solution is sprayed against target pests.

Manzanilla, on the other hand, drives away a wide range of insects. To use it as a pesticide, dried flowers are finely chopped and mixed with fine clay loam and water at the rate of six to seven tablespoons of dried flowers per gallon of water. The mixture is sprayed on infested plant parts.

Tubli has an ancient reputation as a botanical pesticide. Ethnic groups in the Philippines have long been using it to poison unwanted fish. In Brazilian rivers, it is used to eliminate the deadly piranha.

Tubli’s insecticidal properties were discovered in 1848, when the plant was first used against the nutmeg caterpillar. It was patented for use as an insecticide in England during the late 19th century, and American farmers started using it in 1911.

Applied as a powder or spray, tubli is toxic to a wide range of insect pests–aphids, beetles, borers, the diamondback moth, fruit flies, thrips, cabbage worms, fleas, flea beetles, lice, loopers, mites, mosquitoes, psyllids, and slugs. It is recommended for application on bush and vine crops, too.

Another excellent botanical pesticide is kakawate. The United Nations Food and Agriculture Organization (FAO) reports that kakawate 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 FAO said.

Aside from rodents, kakawate also acts potently on insects. 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 Ilocos region, a study made by the Mariano Marcos State University found out that kakawate leaves can be used to control diseases that attack garlic like purple blotch and bulb rot. To prepare the concoction, the leaves are pounded using mortar and pestle. After that, one liter of water is added to a kilogram of pounded kakawate leaves. The mixture is filtered and sprayed to the plants infested by pests.

In the Science City of Munoz, Nueva Ecija, organic rice farmers sprayed their crops with fermented leaves and twigs of kakawate and neem trees to control pests and diseases. Some farmers found it convenient and effective, also, 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 against pests that attack cabbage and broccoli like cabbage butterflies, diamondback moths, leafminers, and inchwoitits.

Many other plants can also be used to prepare extracts with pesticidal properties. A mixture of garlic, onion, marigold, and hot pepper (siting labuyo) can annihilate a wide range of insect pests.

To prepare the concoction, the following are boiled in water for 10 minutes: three to four garlic gloves, two handfuls of marigold leaves, two to three onion bulbs, and two to three small hot peppers. Then, let it cool before diluting the mixture with water four to five times the quantity of the botanical materials. Stir thoroughly and spray on infested parts. The mixture is best used within two days.

“Botanical pesticides are one answer to the pest problem in developing countries,” says Gaby Stoll, a German agrobiologist and author of Natural Crop Protection. However, she sounds a word of warning: Not all botanicals are risk-free. “Some are as dangerous as chemical pesticides,” she warns.

But Stoll says the move from chemical to botanical pesticides is “an important step in the search for a balanced, self-regulating agricultural system.”

Another 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. Therefore, they don’t have a long lasting contaminating effect on the environment.

One disadvantage of botanical products is that they are generally not specific. Many plant extracts will also kill or repel beneficial insects. Just like synthetic pesticides, the botanical products should thus be avoided and only be used as a last resort. However, if a fanner decides, after careful consideration, that active control of a pest is required, botanical extracts are usually a better choice than chemical pesticides.

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.

By Henrylito D. Tacio