Neem Tree (Azadirachta indica)
Azadirachta indica, commonly known as neem, margosa, nimtree or Indian lilac, is a fast-growing tree in the mahogany family Meliaceae, valued as a medicinal plant, as a source of organic pesticides, and for its timber. It is one of the two species in the genus Azadirachta. It is native to the Indian subcontinent and to parts of Southeast Asia, but is naturalized and grown around the world in tropical and subtropical areas. Its fruits and seeds are the source of neem oil.
Neem is usually grown from seed but can be propagated from cuttings or root suckers. The plant is hardy and resilient and grows well in poor, rocky soils. Neem tolerates a wide variety of environmental conditions but cannot survive freezing temperatures or being waterlogged.
Description
Neem trees can reach 15–30 metres (49–98 feet) in height and have attractive fairly dense rounded crowns 20–25 m (66–82 ft) in diameter and thick furrowed bark. Its branches are wide and spreading.
It is evergreen, shedding many of its leaves during the dry winter months. The compound leaves have toothed leaflets and are typically evergreen but do drop during periods of extreme drought. The opposite, pinnate leaves are 20–40 cm (8–16 in) long, with 20 to 30 medium to dark green leaflets about 3–8 cm (1+1⁄4–3+1⁄4 in) long. The terminal leaflet often is missing. The petioles are short.
White and fragrant flowers are arranged in more-or-less drooping axillary panicles which are up to 25 cm (10 in) long. The inflorescences, which branch up to the third degree, bear from 250 to 300 flowers. An individual flower is 5–6 mm (3⁄16–1⁄4 in) long and 8–11 mm (5⁄16–7⁄16 in) wide. Protandrous, bisexual flowers and male flowers exist on the same individual tree.
The fruit is a smooth (glabrous), olive-like drupe which varies in shape from elongate oval to nearly roundish, and when ripe is 14–28 mm (1⁄2–1+1⁄8 in) by 10–15 mm (3⁄8–5⁄8 in). The fruit skin (exocarp) is thin and the bitter-sweet pulp (mesocarp) is yellowish-white and very fibrous. The mesocarp is 3–5 mm (1⁄8–1⁄4 in) thick. The white, hard inner shell (endocarp) of the fruit encloses one, rarely two, or three, elongated seeds (kernels) having a brown seed coat.
The neem tree is similar in appearance to its relative, the chinaberry or bakain, Melia azedarach, with which it may be confused. Melia azedarach also has toothed leaflets and similar looking fruit. One difference is that neem leaves are pinnate but chinaberry leaves are twice- and thrice-pinnate.
Ecology
The neem tree is noted for its drought resistance. Normally, it thrives in areas with sub-arid to sub-humid conditions, with an annual rainfall of 400–1,200 mm (16–47 in). It can grow in regions with an annual rainfall below 400 mm, but in such cases it depends largely on ground water levels. Margosa can grow in many different types of soil, but it thrives best on well-drained deep and sandy soils. It is a typical tropical to subtropical tree and exists at annual mean temperatures of 21–32 °C (70–90 °F). It can tolerate high to very high temperatures and does not tolerate temperature below 5 °C (41 °F). Neem is one of very few shade-giving trees that thrive in drought-prone areas such as the dry coastal, southern districts of India and Pakistan. The trees are not at all delicate about water quality and thrive on the merest trickle of water, whatever the quality. In India and tropical countries where the Indian diaspora has reached, it is very common to see neem trees used for shade lining streets, around temples, schools and other such public buildings or in most people's backyards. In very dry areas, the trees are planted on large tracts of land.
Uses
Nearly all parts of the neem tree are useful, and many of its medicinal and cosmetic uses are based on its antibacterial and antifungal properties. Neem is commonly used in shampoos for treating dandruff and in soaps or creams for skin conditions such as acne, psoriasis, and athlete's foot. It is also a component in some toothpastes and mouthwashes, especially in the Indian subcontinent, and young twigs are used directly as crude toothbrushes in rural areas. Neem leaves have long been used as a traditional treatment for diabetes, and there is some clinical evidence suggesting that it may help control blood sugar levels. Neem oil and neem bark and leaves are unsafe for consumption by pregnant women and can cause miscarriage.
Pest and disease control
Neem is used as an insecticide, providing a natural alternative to synthetic pesticides. Seeds are ground into powder that is soaked overnight in water and sprayed on the crop.
Oil extracted from the seeds can be used directly as an insect and mite repellent, insecticide, and fungicide and is the source of many commercial pesticide products, including dusts, granules, and concentrates. The primary active insecticidal ingredient, azadirachtin, works to disrupt the hormones involved with insect molting, preventing larvae from developing properly into adults, and is a feeding inhibitor. Neem oil can kill soft-bodied insects on contact and decreases mating and reproductive behaviours. Neem also acts as an egg-laying deterrent and suppresses the subsequent hatching of their eggs. All this results in much decresed pest fecundity.
As a fungicide, neem oil is used to control rust, black spot, mildew, scab, anthracnose, and blight.
Given that neem oil breaks down quickly with exposure to ultraviolet light, repeated applications are often necessary, at least every ten days. Neem-based pesticides generally have low toxicity for mammals and are common in organic farming applications.