‘Neem’ — a safe natural pesticide

Published Sep 24, 2007 12:00am

THE neem plant is a member of the family Meliaceae. The evergreen broad-leaved tree can attain a height of 30 metres with a trunk girth of 2.5 metres. It usually has a life-span of over two centuries. The plant’s deep root system is well adapted to retrieving water and nutrients from the soil profile, but it is very sensitive to water-logging.

The tree thrives in hot, dry climates where temperature often rises to 50 degrees Celsius and annual rainfall varies between 400 to 1,200 millimetres.

The tree can withstand environmental adversities, including drought and infertile, stony, shallow, or acidic soils. Neem produces are ellipsoidal drupes about two centimetres in length, arranged on axillary clusters. Fruit yields range from 30 to 100 kilogrammes per tree.

Fifty kilogrammes of fresh fruit yield approximately 30kg of seed, which gives about 6kg of oil and 24kg of seedcake.

Seed viability generally ranges from six to eight weeks, but thoroughly cleaned, properly dried and cooled seeds remain viable up to six months.

These fruits contain kernels that have high concentrations of secondary metabolites. Very little problems arise in vegetative propagation.

This tree has a great medicinal value and has been used for shade, building materials, fuel, lubricant, and above all as pesticides. It also has the unique quality of enriching the surrounding soil and making it more conducive to water retention.

Neem is the most eco-friendly, environmentally “safe” natural pesticide.

Its extracts have severe effects on insects. Neem fruits, seeds, oil, leaves, bark and roots can be used as general antiseptics, antimicrobials, treatment of urinary disorders, diarrhoea, fever, bronchitis, skin diseases, septic sores, infected burns, hypertension, and inflammatory diseases.

Neem oil and its isolates inhibit fungal growth on humans and animals. Neem leaf extracts are used to treat malaria.

Cattle leaf supplements containing neem leaf powder are used as worm killers. Creams containing neem oil are used for animal wound dressing and also act as fly and mosquito repellents.

Neem is also said to aid longevity, guard against heart disease, high blood pressure and arthritis. Besides, it has ingredients which lower cholesterol and clear arteries of fat.

Margosa oil extracted from neem seeds has amazing antiseptic properties as well. It is now being increasingly used in the manufacture of anti-dandruff soaps and toothpastes. The other uses of margosa oil is said to help diabetic patients.

Ancient vaids usually recommended a paste of neem leaves and margosa oil as a cure for obesity. Its cosmetic value too is an established Indian tradition as in the old times women applied an application of neem leaves and turmeric paste for a glowing skin.

Concoctions of neem leaves blended with honey or other soothing herbs are said to cure dermatitis, eczema and other skin rashes.

Dried nimbosterol mixed with honey and pepper powder can cure colds, stop bleeding and help a patient suffering from piles.

Amongst many chemical compounds derived from neem only four are highly effective in their activity as pesticides including azadirachtin, salannin, meliantriol, and nimbin.

Salanin is a potent pest controller and is far more effective than chemically-produced diethyl-toluamide that constitutes as a part of most of the synthetically produced lethal pesticides.

Neem seed oil has also detrimental effects on viruses, mites, and early larval stages of some insects, while solid seed residue has activity on soil borne fungal pathogens and plant parasitic nematodes.

Research has revealed that neem oil causes “solitarisation” of gregarious locust nymphs.

After exposure to doses equal to a mere 2.5 litres per hectare, the juveniles fail to form the massive, moving, marauding plagues that destroy crops trees and all vegetations.

Neem affects grasshopper nymphs similarly. Neem oil enriched with azadirachtin prevents locusts from developing into their migratory swarms. It apparently blocks the formation of the hormones and the pheromones needed to maintain the yellow-and-black gregarious form.

Neem cake has varied uses as livestock feed, fertiliser and natural pesticide. The cake is traditionally littered in rice fields as a fertiliser.

Neem-coated urea (90:10) can save about 30 per cent of the total chemical nitrogen requirement of crops.

Neem seedcake is widely used in India as fertiliser for sugarcane, vegetable and other cash crops.

The cake also acts as a pesticide. When added to soil it protects plant roots from soil-insects and nematodes.

It has been found that beneficial insects like predator and parasitoid insects are relatively unaffected when exposed to neem extracts.

Evidently, azadirachtin does not affect beneficial insects in the same way as it does to pest insects.

Some parasitoids (parasites of pest insects) showed slight toxic affects when emerging from treated mummified hosts.

Earthworms actually benefit from soil application of neem by-products with increased weight gain and more progeny.

And spiders, butterflies, ants, and ladybugs also show no detrimental effects from exposure to neem tree extracts.

The plant has much to offer with regards to solving global agricultural and public health problems.

To help solve these problems, more neem trees will have to be grown to meet the increasing demand for insecticidal and industrial uses.

Additional neem plantings will also serve as a refuge for honeybees, wasps, spiders, birds, bats, and other beneficial organisms, and the litter of falling leaves can improve soil fertility.

Superior ecotypes can be selected to increase the productivity and quality of neem.


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