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.
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.
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/
