If neem lives up to its early promise it will help to control many of the world's pests and diseases, as well as reduce erosion, desertification, deforestation, and perhaps even slow the rate of increase in population. So many details remain to be fleshed out, however, that its practical possibilities cannot yet be seen even to a limited extent.
The fact that neem is a tree is in some sense a limitation; to mass-produce products on a vast scale from trees is much harder than from annual plants. However, trees also have several advantages. They are perennials that will provide their products for decades, they pose little risk of becoming weeds, and, once established, they require little care. Moreover, growing tree crops these days is an advantage in itself. Indeed, resources harvested from trees are of vital importance to this seriously threatened planet. Reforestation contributes to a better world, and neem is a good candidate for global tree planting.
Whether neem will thrive in dense plantation blocks is not absolutely certain, but there are many sites where it seems ideal. It can grow in certain marginal lands, for example, and therefore does not have to displace food production because it can be raised where soils are too worn out for crops. It even benefits certain types of soils and, like all trees, helps reduce erosion.
Harvesting neem fruits does not destroy the tree; unlike most reforestation species, neem is more profitable standing than felled. Thus, the use of neem products has the merit of promoting a greening of the earth.
Despite some unresolved questions, enough is already known that exploiting certain neem uses can begin immediately. Indeed, the global problems posed by pests, diseases, erosion, deforestation, and desertification are so vast that boldness is called for and some risk is
worth taking. This, therefore, is a time for people to bring the plant and its products into international use. An orderly creation of plantations and markets—with reliable availability of uniform, good quality seeds at stable prices—could see neem rise steadily to become one of the most widely grown trees in the world—perhaps eventually rivaling the African oil palm in its value.
Governments, agencies, and individuals that assist developing nations should support the development of neem plantings, underwrite projects to harvest and process the seeds for use in pest control and personal hygiene, and assist countries to develop high-quality ecotypes in terms of azadirachtin content and other desirable traits.
In developing neem, there is potential for much innovation. One example is the concept of centering rural industries around neem-extraction facilities.1 In this system, industrial development would be integrated with neem-tree growing. It might incorporate crops and livestock, but growing neem trees and processing their products would form the core. This integrated combination has a good chance of providing sustainable, self-reliant, and decentralized rural development—a long-sought goal of many economic development programs.2 In addition, it could help national interests by reducing pesticide imports and perhaps increasing exports.
In the coming years, the struggle to keep food out of the jaws of plant-eating pests will increase in importance as human populations increase, living standards rise, demands for quality food (and the consequent emphasis on blemish-free fruits and vegetables) increase, and the public clamor to eliminate synthetic insecticides becomes more insistent. Neem could be the key to opening this new era of safer pest-control products and, if so, is likely to be in huge demand.
Although research on neem-based pesticides is under way, it is only a fraction of what it might be. Currently, there are projects in Australia, Bangladesh, Burma, Canada, Dominican Republic, Germany, India, Israel, Kenya, Nigeria, Niger, Mali, Pakistan, and the United States.3 Nonetheless, most are small, undersupported, and tacked onto other
Preparation of Extracts
There is now enough information to encourage use of the current formulations. However, "low-tech" methods should be devised to extract and formulate neem materials in ways that can easily be undertaken by farmers who grow their own neem trees for their own use.
At present, the quality of neem extracts varies. The differences seem to depend on the way the seed was handled, stored, or extracted, and perhaps other factors yet to be recognized. Thus, research on the optimal handling of neem materials is particularly needed. Topics to be studied include conditions for storing seed before extraction and before use, as well as the effects of storing and handling the extracts after they have been made. Increasing the storage life of neem formulations is vital.
Before mass-producing neem products for international use, standardization is essential. The efficacy of various batches is impossible to compare now because no standard of potency is being used. An international nomenclature for neem ingredients—perhaps defined in ppm of azadirachtin—would help bring some order out of the current chaos.4
Studies of Effectiveness
The potential of neem products as a village-level remedy for the agricultural pests of the tropics should be fully explored. Further research on specific crops and sites, pest organisms, formulations, and application methods is needed.
Modes of Action
Neem derivatives are promising pest control materials, but just how they work on various species is a topic deserving much greater research attention. Basic research to study the effects of neem extracts on hormone regulation and hormone receptors is required.
Formulation of Products
Additional research is also needed to extend the period in which neem products remain active. When sprayed on plants, the extracts
The public's increasing concern for the environment seems likely to result in a rising demand for pesticides from plants rather than from petroleum. Such "soft" pesticides represent the hope that agricultural pests can be controlled while maintaining environmental stability. One American market-research firm estimates that by 1998, total soft-pesticide sales in the United States alone will reach $813 million annually, up from $450 million at present.
Neem may become a major part of that growth, but it is not the first botanical pesticide. Pyrethrins, which are naturally derived from daisy like flowers of certain species of Chrysanthemum, have been used for centuries. Almost 2,000 years ago the Chinese knew that chrysanthemum plants had insecticidal value; some 2,400 years ago the Persians used them. Not until recent centuries, however, were the potentials of the pyrethrins, extracted from the flowers, fully appreciated. Supposedly an Armenian trader, who had learned the secret while traveling in the Caucasus, introduced the insecticide into Europe early in the nineteenth century. Last century, Dalmatia (Yugoslavia) became the center of the world's pyrethrum industry, but after World War I, Japan became the main producer. With supplies cut off during World War II, the Allies began producing the flowers in Kenya. Since the 1960s pyrethrum production has been established in the New Guinea highlands also.
Like neem products, pyrethrins are valued for their low toxicity to mammals and birds. However, the ingredients in these insecticidal chrysanthemums are lethal to insects in a different way from those in neem. They are nerve poisons and contact insecticides. Pyrethrum has quick knockdown properties and is the active ingredient in millions of aerosol spray cans people use against flies and mosquitoes.
Despite the development of many synthetic insecticides, this chemical from chrysanthemums has maintained its position as a major commercial product. World production is more than 10,000 tons. Although powerful synthetic analogues have been developed, demand for the natural material has remained high, and in the past several years it has been in short supply.
Now neem, another botanical pesticide, can perhaps step up to take an equally important, but complementary, role in the rising soft pesticide market.
The product Margosan-O® (see Appendix A) has been tested and certified safe (when used as directed), but more toxicological research on neem extracts is needed. Chronic-exposure tests, higher-mammal studies, and epidemiological evaluations could help identify any potential short- and long-term hazards before massive international use. All in all, appropriate researchers should undertake studies to assess any remaining possibility of toxicity to higher mammals, birds, or fish.
Because of the complexity of the mixtures and their modes of action, it seems unlikely that any resistance to mixtures of neem products will develop in the short run. However, insects have disproved similar projections with previous pesticides too often for complacency. Neem materials should therefore be used circumspectly. If applied by judicious spot treatments at appropriate times, they may remain effective for centuries. On the other hand, if used indiscriminately in blanket sprays, they may induce resistance in the pests and be rendered ineffective within a few years.
The buildup of resistance is much more likely with refined neem formulations based on a single active ingredient from neem, such as azadirachtin. Pests can probably develop resistance to a single neem ingredient about as readily as to other insecticidal compounds.
Further research into the issue of resistance is called for.
Recent surveys reveal that in both India and Pakistan most of the poorer farmers mix a "handful" of neem leaves in their stored grains to protect them from pests. However, the more affluent farmers, although aware of this practice, do not follow it. Some questioned its efficacy, but most did not want to be stigmatized as "backward" for
Many specialized insecticide uses deserve research, especially in tropical areas. One example is neem-based insect-repelling treatments for common products, such as the bags used for holding and shipping food and other perishables.
Neem materials are a vast storehouse of possible pest-control agents of the future. Azadirachtin, meliantriol, and salannin, for instance, might serve as models for the synthesis of insect-feeding inhibitors and growth regulators for controlling stored-grain pests, grasshoppers, locusts, nematodes, and other pests. Even if such synthetic analogues prove commercially feasible, it is unlikely they will cut greatly into the markets for the directly extracted neem materials.
NEEM OIL RESEARCH
Despite centuries of use in India, neem oil is still poorly understood as compared to palm oil, soybean, and other vegetable oils. Some basic chemistry, as well as processing and product-development research should be most useful.
The methods used for processing and refining neem fruits and seeds all need improvement. In particular, simple methods that farmers can employ themselves are comparatively inefficient at present. On the other hand, research on the use of advanced separation technology is also required. Problems of deodorizing, refining, and purifying the oil in industrial production have yet to be made practical and economic on a large scale. Modern separation processes, such as selective adsorption or high-tech membranes, might prove extremely valuable here.
Neem and the Superbug
As we go to press in December 1991, news is sweeping the nation that a deadly insect infestation has destroyed America's winter melon crop and damaged its lettuce, cabbage, broccoli, cauliflower, and carrot crops. Millions of voracious insects have spread over California's Imperial Valley, massing on the undersides of leaves and sucking plants dry, weakening or killing them in the process. American consumers have been told to expect serious shortages of some fruits and vegetables, not to mention soaring prices.
The poinsettia whitefly, or "superbug" as farmers are calling it, is a new, more potent strain of the sweet potato whitefly (Bemisia tabaci). It appears to be pesticide resistant and eats "just about everything" in its path. According to California agriculture experts, asparagus and onions are the only crops that it does not like.
As a result of the tiny fly's attack, California's governor, Pete Wilson, has declared a state of emergency. And no wonder. California farmers have suffered nearly $90 million in damage, more than 2,500 farm workers are out of work, and hundreds of farm-related businesses have had to take huge losses. California's agriculture experts expect that eventually the blizzard-like swarms of tiny flies will destroy $200 million worth of winter vegetables.
What will happen in future years is anybody's guess. California has no native predators that are effective against the superbug, and all the authorized pesticides are largely useless. However, neem is one of the possible answers to the problem. For several years, this very same insect has been one of the prime targets of neem-seed extracts. This was in other parts of the country and on other crops—mainly ornamental plants and mainly in greenhouses. There, neem products have controlled the superbug very effectively, but whether they will be the answer to the problem over the vast areas of vegetables and fruits growing in the Imperial Valley is as yet uncertain.
One major problem is that neem is not registered for use on food crops. Another is the lack of supplies of neem seeds. Nonetheless, even the possibility of a natural pesticide for such a knotty problem is cause for hope that a cure can be found.
Neem soaps, lubricants, and many other consumer products offer exciting promise, especially for tropical countries. Here, too, there is much scope for invention and product development. Basic needs include formulations, analyses, and standards for quality.
Neem opens up many possibilities of new products that could benefit horticulture, silviculture, and agriculture. There is much scope for research and development in this area. It is perhaps not too far-fetched to speculate that the tree's extracts might be employed in the following ways:
As systemic fungicides for treating sick trees or crops;
For preventatives that could stop fungal diseases from establishing themselves in plants;
In treatments for trees diseased by viruses; and
In treatments for crops threatened by garden snails and slugs.
Studies of neem's medicinal values are urgently needed and include the following topics:
Effectiveness in alleviating pain or fever;
Antibacterial and antiviral qualities;
Control of dental cavities and pyorrhea;
Use of neem twigs for teeth cleaning in areas where toothpastes are unavailable or beyond the budgets of poor people;
Topical treatments for lice;
Use of neem-leaf juice and neem oil in the treatment of psoriasis;
Topical treatment for warts;
Treatment for parasites in the human digestive tract; and
Treatment for parasites in the human blood and lymph systems, including those causing malaria, Chagas' disease, river blindness, elephantiasis, and sleeping sickness.
Under normal use, neem apparently affects a variety of organisms, including bacteria, fungi, mollusks, and protozoan parasites, which may
open many avenues for exploratory research in veterinary medicine. Traditionally, Indians have rubbed neem products onto livestock to treat various complaints. Research should be undertaken to confirm the ability of neem oil or neem-seed extracts or a combination of both to repel insects and ticks, as well as to soothe cuts and bruises and to cure scabies. Neem may also help with several serious tropical skin parasites—those that cause mange in camels and donkeys, for example.
Neem products should also be tested as a treatment for intestinal parasites, such as roundworms and tapeworms. The oil's efficacy in the treatment of infections, particularly of the genital tract (postpartum inflammations of the uterus, for instance) in animals also deserves attention.
Individual neem trees vary greatly in their morphology and perhaps in their chemical makeup. It is not yet understood whether these differences are based on genetics or environment or both, although it is believed that environmental factors (such as drought stress) play a dominant role. Basic research is needed in this area and will have to be carried out mainly in Asia, where the greatest range of genotypes is to be found.
So far there has been no selection or breeding for maximum pesticide production. One approach is to seek out the trees whose seeds have the highest proportion of azadirachtin. This would have to be done using standardized methods to ensure that differences in seed handling, deterioration, and other features do not interfere. A major breakthrough would arise here if the azadirachtin content can be correlated with a visual or readily identified feature of the trees or seedlings. With millions of neems in the world, a rapid qualitative assessment would be most valuable at this time.
The second approach is to select trees that yield maximum numbers of large fruits. The number and weights of fruits on different trees vary greatly, and obtaining the maximum yield of kernels may be economically more important than the percent of azadirachtin in each kernel.
Biotechnology research that might benefit neem includes:
Magnifying desired traits;
Examining the enzymology and gene expression of limonoid production;
Transferring neem's pest-resistance genes into agriculturally significant plants; and
Genetically mapping neem's DNA. (This will speed the development of neem products and benefits.)
Much valuable research could be done in the area of neem silviculture. This might include assessments of the following:
Lateral (feeding) root effects.
Other beneficial soil microbes.
Seed viability. (Research is particularly needed to develop methods to extend the period of the viability of neem seeds for replanting.)
Rapid establishment. (At present, the horticultural conditions and practices that lead to optimal growth or production are unknown. Needed are ways to speed up establishment of the trees.)
Provenance selection (selection of genotypes better suited for select sites—relatively dry areas, for instance).
In addition to such silvicultural studies, neem's apparently remarkable ability to survive in cities and to withstand excessive heat, as well as survive air and water pollution should be evaluated. This could well boost its use in urban forestry throughout the tropics.
The possibility of selecting genotypes for the production of various types of wood products should also be examined.
One need is for types with straight trunks and a maximum length of clean bole. These would be used to produce construction lumber.
Another need is for easy-pollarding types suitable for producing building poles. In several countries neem poles are more valued than any other neem products. Genetic selection for optimum branching from a stump cut close to the ground could be helpful here, as could research to determine the best time of the year and the best height at which to cut the trees. Rural producers in Burkina Faso already manage their neems like hedges (tenkodogo) to harvest building poles more easily.
Frequent coppicing or pollarding are not conducive to good flowering because they severely restrict the growth of lateral (flower-bearing) branches. This, in turn, reduces the production of fruit. Therefore, to grow neem for its seed and oil requires a different approach.
A neem-fruit plantation of the future will likely consist of trees specially selected for high yields of high oil-bearing seeds and widely spaced to allow for an optimum spread of the lateral branches and an unrestricted formation of the flowers. Producing and managing these plantations has little in common with conventional forestry. Indeed, it is more in the domain of pomology: the art and science of cultivating fruit trees. Sophisticated modern techniques such as clonal selection, tissue culture, pruning, grafting, mulching, and fertilizing with major, minor, and trace elements are all research requirements.
Clarification of such features is important. Neem orchards established in this way could provide a regular supply of quality seed and oil—and thereby become the basis for a thriving international industry based on neem ingredients.
By and large, neem appears to be a poor companion for field crops. However, certain plantings might prove suitable for integrating with local farming and grazing practices. Further investigation should be made. Farming systems combining neem, fast-growing timber trees, and shrubs as a combination fallow would likely turn around declining ecosystems of many humid and semiarid tropics while providing a continuing income. Such systems may help restore and maintain soil fertility.
In certain old (1920s) experiments it was reported that neem-leaf extracts seemed to overcome viral diseases in beans, tobacco, and some other crops. This could prove to be of outstanding importance. On the other hand, the results were inconsistent and there is likelihood that they will prove unrepeatable.
Nonetheless, if neem shows even limited antiviral activity, that alone would be of interest to world agriculture. The fact that its compounds are systemic and that the tree grows in many countries where viruses devastate crops (streak virus in Africa's corn is an example) are additional benefits of possibly enormous consequence. This is a shot in the dark, but worth exploring.
Asians have long used neem to treat bacterial diseases of the skin (see Chapter 7), but, at least for now, its use to combat bacterial diseases of plants is a research area wide open for exploration.
Neem (Azadirachta indica) has at least two close relatives, A. siamensis and A. excelsa. They, too, are promising resources.
A. siamensis is known as ''edible neem" because its young leaves and flowers contain lower amounts of bitter principles than A. indica and are consumed in considerable quantities as a vegetable by people in Burma and Thailand. No negative consequences have been reported. A. siamensis also contains azadirachtin in its seed kernels and might be a useful source of pest-control materials as well as food.7
A. excelsa is a little-known tree of Southeast Asia. Recently, German researchers have isolated and characterized a new limonoid from its seed kernels. This compound, marrangin, shows the same mode of action as azadirachtin but is two to three times more active. Leaf extracts of A. excelsa also show a better efficacy than those of neem itself. 8