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Zero tillage, by leaving a permanent surface mulch, reduces rain impact and erosion enormously (by 95% in LEVER some trials). This is an economic benefit of significant national importance to the Brazilians. Short-term economic benefits accrue to the farmer in savings of diesel fuel, increased area planted per man-hour, improved timeliness of planting and, in the Brazilian rotation, increases in wheat yield (though not soy bean yield) due to improved moisture conservation and soil quality [13], and reductions in the number of terraces and their construction cost.

Analogous benefits from herbicide-induced mulches have been shown in tea in East Africa [14] and in Assam and in young oil-palm in Malaysia [15] where financial savings in weeding costs were augmented by yield benefits through avoidance of root pruning, soil conservation and improved nutrient uptake.

Another example of a change of system is illustrated in the Philippines where herbicides are playing an important part in radical changes of cultural practice. Increased availability of irrigation and more rapidly maturing varieties have made double cropping of rice possible.

The growth of non-agricultural employment, however, has resulted in a shortage of labour to meet requirements at the peak transplanting time. One solution to the labour shortage problem has been a switch to direct seeding, a change which was only possible because of the availability of suitable herbicides to control the much more severe weed growth which accompanies the growth of direct-sown rice seedlings. In this situation hand weeding is not a practical alternative to chemical use because of mechanical damage caused by people moving through the crops, the very small size of weed seedlings at the early critical stages of crop growth and the difficulty of telling grass weeds from rice seedlings.

While the specific contribution of the herbicide cannot be quantified, the change in system has resulted in dramatic increases in yield per hectare per year.

In addition to benefits accruing to pesticide users through increased value of agricultural output, there is also a wider benefit to the community in the lower food prices which accompany increases in supply. Borlaug [16], for example, estimated that a total ban on pesticide use would not only result in production losses of 50% but could also cause price rises of 4 or 5-fold.



While a number of examples has been given to illustrate the rewards which can accrue as a result of pesticide use, the extent to which those benefits are realised will vary considerably between situations. In addition the influence of cost and price factors, such as the cost of the.specific pesticide, the cost of labour and the value per tonne of 4 the treated crop, rewards will be affected markedly by the overall level of crop management and the efficiency of pesticide use in relation to levels of pest incidence.

The economic benefits to be derived from protecting a crop against yield losses caused by insect attack or weed competition will be much greater where high-yielding cultivars are grown under good management practices with adequate fertilizer and water than under poorer, lower input management regimes. This has been illustrated above.

In the contrasting agricultural environment of many poor peasant farmers, only very limited amounts of cash will be invested in the production system. Seed will be saved from previous seasons and labour will be provided by the family. For many of them, yields depend more on the luck of good rainfall at critical stages of crop growth than on avoidance of any losses due to pests or weeds.

Expenditure on pesticides, rather than being a good insurance policy can, in these circumstances, be a new burden of debt which cannot be financed and may not be economically justified.

Within a particular production system and cost structure,

the cost effectiveness of pesticide use depends upon:

(a) selection of the correct chemical for the problem to be solved (b) correct application timing in relation to crop growth, and pest level (c) correct application at the chosen time (d) other associated costs, eg costs of application.

Compound selection must reflect both cost-effectiveness against the target species and spectrum of activity in relation to the target pest complex and the ecology of predators.



COWPEA CULTIVARS 1973 (IITA Data, Ref. [17])

–  –  –

* MR = moderate resistance; S = susceptible to leaf hoppers and thrips.

Economics of application can vary considerably with application timing. This- is exemplified by studies of insecticide use on cowpeas in northern Nigeria [17] Table 5.

On varieties moderately resistant to leaf hopper and thrips, insect attacks prior to flowering do not cause levels of injury sufficient to result in economic loss, and plants can recover from moderate to heavy defoliation. Early insecticide applications have no economic merit. Attacks during the critical flowering and pod formation stage, however, cause severe losses and justify chemical use to give yield increase of about 200% [18].

Greater insecticide use can be justified early in the season on the more susceptible variety. As with many high-yielding varieties, genetic potential for yield is often gained at the expense of pest or disease resistance and the variety has to be grown with high levels of other inputs to achieve its potential.

Method of application is important to economics. Many traditional application methods are very crude and the proportion of the applied dose reaching the pest is often small. Unskilled operators often apply wrong rates in the wrong way. This can be improved through good training and also advances in application technology.

IAEA-SM-263/40 such as electrostatic spraying, which can result in more accurate chemical placement, reduced rates of application and reduced application costs (e.g. through reduction in water carrying) [19].


The use of biologically active chemicals to achieve particular agricultural benefits carries with it the risk of side effects on humans and non-target organisms in the environment. As the use of crop protection chemicals has become more widespread, so has the awareness of the risks [20], and it is important that hazards to users, food consumers and the environment are fully considered in the economic equation. In the early period of widespread pesticide use, during the late 1940s and 1950s, DDT and other novel compounds were accepted as the salvation from insect pests of a wide range of agricultural crops. Its use gave large increases in yield, and the World Health assembly of 1955 proposed the use of DDT for a global malaria eradication programme. However, by 1962, with the publication of Silent Spring [21], vigorous debates were starting on whether the risk : benefit equation was tilting in favour of, or against, pesticides. During the last two decades there has been increasing concern about the toxicological and environmental consequences of chemical use and increasingly stringent government regulation of the industry, much of which is reflected by the other topics of this conference. The increasingly stringent regulation has increased the cost of new product development by highlighting the need for a very wide range of toxicological and environmental studies as part of the development programme (Table 6).

The average cost of developing a new pesticide is now about $25 m and still rising fast. This means that new pesticides, for which there is a large dossier of data on toxicology, fate in food and in the environment from which to make risk:benefit judgements, are inevitably more expensive than the old "commodity" compounds.

Government authorities have to make a judgement on whether to purchase cheaper, possibly more hazardous compounds, or more expensive, newer products upon which risk:benefit judgements can be more fully made.

Decisions have to be taken between financial pressures and the hazards posed by the poor control and misuse of toxic chemicals by peasant farmers.




–  –  –

The balance of the equation will differ from country to country.

Consider, for example, the question of the use of DDT.

DDT use has been restricted in many developed countries, partly because governments have taken the view that society should pay the financial cost of more expensive chemicals in return for a reduction in the environmental concern associated with a compound which is environmentally persistent, accumulates in body fat, tissue and concentrates in the food chain. In the developing world, where DDT still forms an important part of the malaria control programme, shortage of funds and, perforce, other economic priorities tip the balance of judgement in favour of financial rather than environmental considerations. The reduction in environmental risk in moving from DDT may not justify the diversion of scarce foreign exchange from other priorities. Also concern about possible hazards is reduced by the more rapid degradation of the compound under tropical conditions.

Major areas of risk not covered by legislation, of particular concern with insecticides, are those of resistance and resurgence. There is a serious danger that, in maximizing the short-term economic gains which result from liberal use of broad-spectrum insecticides, economic problems could be generated for the future. This is another area well covered by Metcalf [20].

Insect resistance was first observed in 1914 when San Jose scale (Aspidiotus pernicious) became resistant to lime sulphur. Since then the number of carefully documented cases of species/chemical group resistance patterns has grown (Table 7).

Many show multiple or cross-resistance to several groups of insecticide.

Insect resurgence is also an increasing problem. Pests which were not of economic importance can become inqsortant because their predators are destroyed, or pest species which are temporarily controlled by pesticides resurge as greater problems because of loss of their predators. A number of important examples exist.

Spodoptera exigua and Trichloplusia ni arose as problems on central American cotton following use of broadspectrum insecticides during the 1960s. In South-East Asia leaf hoppers and plant hoppers of rice (and virus transmitted by them) became a major problem of the 1970s.

LEVER because their predators were decimated by DDT and BHC used for control of stem borers (Chilo suppressalis and Tryporyza incertulus).

Fortunately the international chemical companies have been able to invent new groups of chemicals to replace those which are no longer able to cope. The indiscriminate use of one weapon, and its replacement with a newer more expensive weapon when the first is no longer effective, is unlikely to be the most economically efficient process. It is a treadmill to which the international agricultural community can easily be committed through unskilled product use and short-sighted economics. It is a risk that may be exacerbated by the ambitions of developing countries to have their own pesticide manufacture, locking themselves into certain types of compound.

Long-term economic gain must come from well considered use of the correct chemical at the correct time; taking note of economic thresholds; rotating chemical types;

making maximum use of natural enemies; tailoring application rates to the pest pressure and the economic degree of control (which may not be 100%).

The optimum long-term use of pesticides, integrated into the agronomic, ecological and socio-economic system (integrated pest control) will not happen automatically.

It must be the result of good adaptive research and extension.

In many cases, improved pest control programmes can be developed with existing pesticides. Development of more sophisticated integrated programmes using novel chemicals with greater selectivity than those currently available, however, requires a much closer partnership between governments and chemical companies to ensure that the potential value of the selective chemicals is fully exploited; farmers will be purchasing a pest management programme rather than cheaper, cruder weapons.


The previous sections of this paper have illustrated the need for increased agricultural productivity, and the valuable contribution chemicals can make. They have also highlighted the complexity of the adaptive research needed to exploit pesticides effectively and the need for IAEA-SM-2241/40 local understanding of the balance between risk and reward. It is vital that good technical and economic information is disseminated to pesticide users through a well organised extension system if the full long-run economic benefits are to be gained. Every effort must be made to avoid long-run economic penalties through misguided attempts to obtain short-term gains.

Haskell [2] highlighted the tendency for many developing countries to give low priority and status to research on the optimum use of pesticides and their integration into ecologically sound agricultural systems and to underplay the necessary infra-structure of extension to convert this local adaptive research to practice. Yet investment in good adaptive research and extension is a vital part of the overall investment in pesticides, and an investment which can bring very large rewards for low capital commitment.

It is also probable that the training of farmers and their advisors will have to proceed a long way before alternative more sophisticated and specific pest control techniques, such as pheromones or sterile insect release [22] can make a major impact on the pest control programmes of the developing nations.

UNDP and FAO are taking more initiative to develop international support for plant protection. The closer the integration between the skills of the chemical industry, independent research and extension, the greater will be the economic return to pesticides and the growth of agricultural productivity.

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