By Henrylito D. Tacio

Davao,  10 September 2009. 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 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.

Botanical Pesticides are Making a Comeback

As a response to such health concerns, the use of botanical pesticides is now fast gaining wider acceptance among farmers.  Botanical pesticides are derived from plants which have been shown to have insecticidal properties.

“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.”

Previously, botanical pesticides are 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 is 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.”

However, she warns:  Not all botanicals are risk-free.  “Some are as dangerous as chemical pesticides,” she warns.

Pros & Cons of Going Botanicals

 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 farmer decides, after careful consideration, that active control of a pest is required, botanical extracts are usually a better choice than chemical pesticides.

Some Popular Botanical Pesticides

Many plants have insecticidal properties. Extracts of these plants can be sprayed on the crop to either kill or repel insects.  

• Atis is best for use against aphids, ants and other crawling insects.  The seed of the fruit is crushed and mixed with water.  The solution is sprayed on target pests.
• Manzanilla 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

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.

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. 

“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.

In Science City of Muñoz, organic rice 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.

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.

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.

Apart 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 that kakawate leaves are effective in controlling diseases that attack garlic like purple blotch and bulb rot. 

To prepare:   

1. Pound the kakawate leaves using a mortar and pestle.  
2. Add one liter of water to a kilogram of pounded kakawate leaves.  The mixture is filtered being sprayed to the plants infested by pests.

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

To prepare: 

1. Boil water for 10 minutes.
2. Add three to four garlic gloves, two handfuls of marigold leaves, two to three onion bulbs, and two to three small hot peppers.
3. Let the mixture cool.
4. Dilute the mixture with water four to five times the quantity of the botanical materials.  
5. Stir thoroughly and spray on infested parts.  

The mixture is best used within two days.

Other means of pest control

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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