Using neem to ward off damage specially to stored grains by pests is known in India since long. Mixing dried neem leaves to save grains, and woolen cloth is a regular practice. But a systematic work to exploit neem for insect control is recent. A few results of these activities are mentioned here. Neem has been found to contain several types ofchemicals, many still unknown, that can be used for managing varied types of pests.
They also act in many ways: antifeedant (saving the crop or itself from being fed upon by insects), attractant attracting the pests actively), repellent (repelling me pests outright) insecticide (killing some insects), nematicide (killing the nematode worms), growth disrupter (breaking down the growth processes of the pests) and antimicrobial (destructive of the microbes).
1. Antifeedant: Neem has been shown to be uniquely resistant to being fed by locusts. As low a concentration of 0.1% of neem seed powder (fresh) mixed in water was able to provide complete locust protection to the treated foliage. Infact this is now a recommended measure to protect agricultural crops from locust invasions.
Mixing 1-2% of neem kernel powder in grain has been demonstrated to give protection to stored wheat, maize, jowar, paddy and pulses over a period of one year from several species of insects, 12% neem oil emulsion sprayed on standing paddy crop suppresses feeding by the hopper insect. The most ready-to-use-antefeedant is provided by the neem cake, the residue left after extraction of oil from its seeds:
2. Attractant: Adults of white grub is a serious pest for many valuable crops. An interesting way to control them is to insert the neem twigs with leaves in rows in the infected pockets around sun-set at the start of the monsoon. At dusk large number of beetles collect on these twigs which are then killed mechanically or chemically.
3. Repellent: Neem repels many insects. White ants simply move away from neem treated areas. Neem cake has been actively used in cleaning termite infested areas of Madhya Pradesh. Neem oil is a strong deterrent to egg laying by potato tuber moth.
4. Insecticide: Neem does have low to moderate toxicity particularly to soft bodied insects. Water suspension of neem seed kernel easily kills Aphis and Saisehia insects. Neem oil extractive kills the mosquito larvas instantly. This is a very important finding. For, the usual petro products used here are too costly and injurious as well, in areas like irrigation tanks, water channels and village ponds, where neem is the ideal replacement.
5. Nematicides: Nematode infection is a serious damage for many crops and the usual memiticidal chemicals are prohibitively costly. Neem cake is proving a very useful substitute here. More importantly, it has been seen that using sodium, potassium and other chemical fertilisers alone would increase nematode population as well. But if applied with neem, nematode population dwindles down significantly.
6. Growth Disrupters: Normal harmonal balance of insects is interfered with by these chemicals. As such they are valuable measures in insect control. Neem possesses this property in a remarkable way. It can penetrate egg shell and effect the developing embryo. Mosquito larvas rared experimentally on a medium containing neem oil extractive just failed to emerge as adults.
7. Pesticide Degradation of the Soil: Pesticides applied to soil in course of time get degraded due to the activity of the soil bacteria. This is good in the sense that persistent compounds are eliminated. But this also hampers getting residual effectiveness. Using neem prolongs the field life of soil insecticides in general. This is of special value for paddy cultivation. Very interestingly again, while using neem cake prolongs the field life of carbofuran, the insecticide used here, it also increases the availability of nitrogen so valuable to the rice plant.
8. Neem Oil and Cake: Only 20% of our annual production of these two valuables are utilised at present; oil, industrially (leather dressing, soap, lubrication) and medicinally and cake, as a manure and cattle and poultry feed. Oil is used for lighting, heating and lubricating machinery. The main problem in using oil is its odour.
But patented processes have been developed in India to convert this oil into pale coloured and completely deodorised fatty acids suitable for high quality soaps. Very significantly, it has been discovered in India that neem oil can be converted to “Polyol” to substitute a similar petroleum product— polypropylene glycol used as a propellant fuel. The value of this discovery in these days of petrol scarcity can hardly be imagined.