Agriculture

Neem: A Tree for Solving Global Problems

Neem is a fascinating tree. On the one hand, it seems to be one of the most promising of all plants and may eventually benefit every person on the planet. Probably no other yields as many strange and varied products or has as many exploitable by-products. Indeed, as foreseen by some scientists, this plant may usher in a new era in pest control, provide millions with inexpensive medicines, cut down the rate of human population growth, and perhaps even reduce erosion, deforestation, and the excessive temperature of an overheated globe.

Native to India and Burma, neem is a botanical cousin of mahogany. It is tall and spreading like an oak and bears masses of honey-scented white flowers like a locust. Its complex foliage resembles that of walnut or ash, and its swollen fruits look much like olives. It is seldom leafless, and the shade it imparts throughout the year is a major reason why it is prized in India. The Subcontinent contains an estimated 18 million neem trees, most of them lined along roadsides or clustered around markets or backyards to provide relief from the sun.

Under normal circumstances neem's seeds are viable for only a few weeks, but earlier this century people somehow managed to introduce this Indian tree to West Africa, where it has since grown well. They probably expected neem to be useful only as a source of shade and medicinals?especially for malaria?but in Ghana it has become the leading producer of firewood for the densely populated Accra Plains, and in countries from Somalia to Mauritania it is a leading candidate for helping halt the southward spread of the Sahara Desert.

This century, people took neem seed to other parts of the world, where the tree has also performed well. Near Mecca, for example, a Saudi philanthropist planted a forest of 50,000 neems to shade and comfort the two million pilgrims who camp each year on the Plains of Arafat (a holy place where the prophet Muhammad is said to have bidden farewell to his followers). And in the last decade neem has been introduced into the Caribbean, where it is being used to help reforest several nations. Neem is already a major tree species in Haiti, for instance.

But neem is far more than a tough tree that grows vigorously in difficult sites. Among its many benefits, the one that is most unusual and immediately practical is the control of farm and household pests. Some entomologists now conclude that neem has such remarkable powers for controlling insects that it will usher in a new era in safe, natural pesticides.¹Extracts from its extremely bitter seeds and leaves may, in fact, be the ideal insecticides: they attack many pestiferous species; they seem to leave people, animals, and beneficial insects unharmed; they are biodegradable; and they appear unlikely to quickly lose their potency to a buildup of genetic resistance in the pests. All in all, neem seems likely to provide nontoxic and long-lived replacements for some of today's most suspect synthetic pesticides.

That neem can foil certain insect pests is not news to Asians. For centuries, India's farmers have known that the trees withstand the periodic infestations of locusts. Indian scientists took up neem research as far back as the 1920s, but their work was little appreciated elsewhere until 1959 when a German entomologist witnessed a locust plague in the Sudan. During this onslaught of billions of winged marauders, Heinrich Schmutterer noticed that neem trees were the only green things left standing. On closer investigation, he saw that although the locusts settled on the trees in swarms, they always left without feeding. To find out why, he and his students have studied the components of neem ever since.

Schmutterer's work (as well as a 1962 article by three Indian scientists showing that neem extracts applied to vegetable crops would repel locusts) spawned a growing amount of lively research. This, in turn, led to three international neem conferences, several neem workshops and symposia, a neem newsletter, and rising enthusiasm in the scientific community. By 1991, several hundred researchers in at least a dozen countries were studying various aspects of neem and its products.

Like most plants, neem deploys internal chemical defenses to protect itself against leaf-chewing insects. Its chemical weapons are extraordinary, however. In tests over the last decade, entomologists have found that neem materials can affect more than 200 insect species as well as some mites, nematodes, fungi, bacteria, and even a few viruses. The tests have included several dozen serious farm and household pests?Mexican bean beetles, Colorado potato beetles, locusts, grasshoppers, tobacco budworms, and six species of cockroaches, for example. Success has also been reported on cotton and tobacco pests in India, Israel, and the United States; on cabbage pests in Togo, Dominican Republic, and Mauritius; on rice pests in the Philippines; and on coffee bugs in Kenya. And it is not just the living.

Neem is a member of the mahogany family, Meliaceae. It is today known by the botanic name Azadirachta indica A. Juss. In the past, however, it has been known by several names, and some botanists formerly lumped it together with at least one of its relatives. The result is that the older literature is so confusing that it is sometimes impossible to determine just which species is being discussed.

Neem trees are attractive broad-leaved evergreens that can grow up to 30 m tall and 2.5 m in girth. Their spreading branches form rounded crowns as much as 20 m across. They remain in leaf except during extreme drought, when the leaves may fall off. The short, usually straight trunk has a moderately thick, strongly furrowed bark. The roots penetrate the soil deeply, at least where the site permits, and, particularly when injured, they produce suckers. This suckering tends to be especially prolific in dry localities.

Neem can take considerable abuse. For example, it easily withstands pollarding (repeated lopping at heights above about 1.5 m) and its topped trunk resprouts vigorously. It also freely coppices (repeated lopping at near-ground level). Regrowth from both pollarding and coppicing can be exceptionally fast because it is being served by a root system large enough to feed a full-grown tree.

The small, white, bisexual flowers are borne in axillary clusters. They have a honey like scent and attract many bees. Neem honey is popular, and reportedly contains no trace of azadirachtin.

Neem is thought to have originated in Assam and Burma (where it is common throughout the central dry zone and the Siwalik hills). However, the exact origin is uncertain: some say neem is native to the whole Indian subcontinent; others attribute it to dry forest areas throughout all of South and Southeast Asia, including Pakistan, Sri Lanka, Thailand, Malaysia, and Indonesia.

It is in India that the tree is most widely used. It is grown from the southern tip of Kerala to the Himalayan hills, in tropical to subtropical regions, in semiarid to wet tropical regions, and from sea level to about 700 m elevation.

As already noted, neem was introduced to Africa earlier this century (see sidebar, page 85). It is now well established in at least 30 countries, particularly those in the regions along the Sahara's southern fringe, where it has become an important provider of both fuel and lumber. Although widely naturalized, it has nowhere become a pest. Indeed, it seems rather well ''domesticated": it appears to thrive in villages and towns.

Over the last century or so, the tree has also been established in Fiji, Mauritius, the Caribbean, and many countries of Central and South America.-In some cases it was probably introduced by indentured laborers, who remembered its value from their days of living in India's villages. In other cases it has been introduced by foresters. In the continental United States, small plantings are prospering in southern Florida, and exploratory plots have been established in southern California and Arizona.

The tree is easily propagated?both sexually and vegetatively. It can be planted using seeds, seedlings, saplings, root suckers, or tissueculture. However, it is normally grown from seed, either planted directly on the site or transplanted as seedlings from a nursery.

The seeds are fairly easy to prepare. The fruit drops from the trees by itself; the pulp, when wet, can be removed by rubbing against a coarse surface; and (after washing with water) the clean, white seeds are obtained. In certain nations?Togo and Senegal, for example?people leave the cleaning to the fruit bats and birds, who feed on the sweet pulp and then spit out the seeds under the trees.

It is reputed that neem seeds are not viable for long. It is generally considered that after 2-6 months in storage they will no longer germinate. However, some recent observations of seeds that had been stored in France indicated that seeds without endocarp had an acceptable germinative capacity (42 percent) after more than 5 years.

Source of Article: http://www.nasonline.org/

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Agriculture