Neem is a versatile plant showing a large number of medicinal, biopesticidal and dyeing properties.
All the parts of the plant contain diterpenoids like margolone and large number of limonoid bitter principles. The stem bark yields nimbin, nimbidin, -sitosterol, tannins (12%) and a gum. Root bark also contains nimbin and nimbidin. Leaves contain nimbin, nimbinene, 6-desacetylnimbinene, nimbandiol, nimbolide, quercetin and -sitosterol. The fruits are found to contain gedunin, azadirachtin, 7-deacetoxy-7-hydroxy gedunin, azadiradione, azadiradone, 17--hydroxy azadiradione, 17-epi azadiradione and nimbiol. Seeds yield oil and a number of bitter principles both in oil and outside. The oil consists of oleic (56%), palmitic (16%), stearic (14%) and linoleic (9%) acids and 0.8% unsaponifiable matter containing nimbidin, nimbin, nimbinin, meliantriol as major components along with gedunin, meldenin, desacetylgedunin, salannin, azadirone, epoxyazadirodione, vepinin, nimbinene, 6-o-acetyl nimbandiol etc. The steam volatile fraction of oil contain a number if di- and trisulphides.
The proven medicinal properties.
1. “Nimbidin”, the crude fraction containing unsaponifiable fraction (mainly limonoids) is used against fungal, bacterial and parasitic infections like eczema, ringworm, scabies, Mycobacterium tuberculosis (in vitro).
2. Nimbidin is antiulcer and antihistaminic in nature and used against peptic and duaodenal ulcers and against Helicobactor pylori.
3. Leaf extract is effective against measles virus (in vitro) and fowl pox and twigs helps in oral hygiene.
4.The plant is antimalarial in nature, even against Plasmodium falciferum.
5.Nimbidin and bark extract are antiarthritic and anti-inflammatory used against a number of rheumatic afflictions.
6. Leaves are hypoglycemic (diabetes) and hepatoprotective.
7. Leaf extracts are shown to have hypotensive and anxiolytic properties. It is also used against atherosclerosis and heart attack.
Pesticidal properties
Almost all limonoids of this plant show insect repellence or suppression; seeds or seed kernels provide the largest amounts of insecticidal compounds. Azadirachtin is extracted in methanol (from seeds). They are safe to use for man and other mammals.
The effects of neem include repellence, feeding deterrence, oviposition deterrence, reduced growth and development and interference with reproduction. Neem is most effective on soft bodied immature stages of plants including whiteflies, thrips, mealy bugs and various caterpillars.
In general, Leaf extract is used against aphids, Colorado beetles, grass hoppers, grubs, Japanese beetles, leaf hoppers, locusts, scales, snails. Seed powder (Aqueous extract.) is preferred for cotton boll worm, aphids, colarado beetles, cotton leaf roller, cutworm, diamond back moth, fall armyworm. Seed oil suspension (with soap) is applied for aphids, plant hopper, flea beetle, leaf hopper, potato tuber moth, psyllid, scale insects, white flies, whorl maggot.
The leaves are used as insect repellents and are kept among clothes and books. The dried leaves when mixed with the grains of wheat and sorghum is used to provide protection against moth (Ephestia cantella Walker), rice weevil (Calandra oryzae Linn), red flour beetle (Trifolium castaneum Herbst.) grain moth (Sitotroga cerealella Olivier) and grain borer (Rhizopertha dominica). Larvae of Lucerne weevil and locust (Schistocerca gregaria Forsk.) are the other organisms repelled or destroyed by the leaves. The pulp extract of fruit also is used against locusts. The powdered fruit/kernel mixed with wheat or legumes (green gram, cow pea or pea) are used against rice weevil (Sitophilus oryzae Linn.) lesser grain borer (Rhizopertha dominica) khapra beetle (Trogoderma granarium Everts), bruchid (Callosobruchus maculatus and flour beetle. The anti-feeding property is attributed to azadirachtin and salanin. But the crude preparations of kernel are found to be more effective than refined ones. Other insects on which the kernel exhibited a toxic/deterrent activity are Locusta migratoria, Schistocerca gregaria, Spodoptera litura and Boarmia (Ascotis) selenaria. The essential oil from seeds is found to be effective against pulse beetle and Callosobruchus sp. The oil cake also is used as an insecticide and nematicide
When the natural neem oil is removed from the seeds and treated with alcohol, virtually all of the azadirachtin and related substances separate from the oil itself. The remaining oil - without the azadirachtin - is called Clarified Hydrophobic Extract of Neem Oil. Unlike azadirachtin, this active ingredient is also active against fungal diseases such as mildews and rusts.
Azadirachtin and clarified hydrophobic extract of neem oil are used for many food and non food crops. Adverse effects to humans are to be avoided and this insecticide should not be applied when honeybees are actively visiting the flowers. Safe for indoor plants.
Azadirachtin interferes with the normal life cycle of insects including feeding, moulting, mating and larvae and thus deter certain insects like locusts from feeding
Neem leaves, kernel and oil cake are found to be effective against nematodes such as Hoplolaimus indicus, Rolylenchulus reniformis, Tylenchorhynchus brassicae, Meloidogyne incognita and M. halpa. Treatment of the seeds of tomato with crude extracts of the seeds of Azadirachta indica, inhibited the penetration of Meloidogyne javanica into tomato roots (Prot and Kornprobst, 1983).
Natural Dye
Bark extract yields condensed tannins including procyanidins and other proanthocyanins. Used mainly for wool and cotton this dye produces a range of beige to brown tones.
Neem wood.
The wood is fairly hard, even and close-grained which seasons well. Having a pretty grain and fine red colour this wood is used for cabinet work and picture frames.
Source : Useful Herbs of the Planet Earth, by M. Daniel, (2012), Scientific Publishers, Jodhpur, Pages 710.
Mammen Daniel
