The neem tree (Azadirachta indica A. Juss) thrives almost anywhere in the tropical lowland, upto 800 m above sea level. It is resistant to extreme drought and grows where the annual rainfall is as sparse as 300 mm. Moreover, it grows very quickly and makes few demands on the soil fertility. The neem tree, therefore, grows in a wide variety of places. Hilltops and infertile, depleted land (e.g., Eroded hillsides) are as suitable as stony, flat land or hard laterite. The neem tree may be used to line avenues, to border roads or fields and in mixed cultivation with fruit trees. The average annual fruit yield from a mature neem tree is above 20 kg. Apart from insecticides, neem oil may be extracted from the seed. 30 kg neem seeds produce 6 – 8 kg oil. The resulting residue can be used to make insecticides in a similar way as from the whole neem seeds described earlier.
All parts of the neem tree can be utilized. Insecticidal substances are present in various parts of the tree; the highest concentrations are, however, contained in the seeds.
Azadirachtin, the most important insecticidal substance contained the plant, has, even in very small doses, a growth disrupting effect on many insect larvae, i.e. insects which eat this substance are unable to develop to the next larval / nymphal stage and die off. Other pests, such as grasshoppers, avoid or reduce feeding as a reaction to azadirachtin. As tests have repeatedly confirmed, due to its special mode of action, the neem extract is quite harmless for useful insects. Unlike synthetic pesticides, tests carried out over a longer period indicate that development of any resistance to the neem extract is in the short term unprobable. However, where intensive vegetable cultivation is practiced, the exclusive use of neem extract is inadvisable.
One great advantage of the neem extract is that even after repeated application on vegetable crops, it remains perfectly harmless for humans.