This section covers integrated pest management (IPM) including biological control, and techniques that are compatible with the use of biological control or minimize negative impact on natural enemies.

Rational Pesticide Use: an Alternative Escape from the Treadmill?

IPM is a strategy that aims to optimize all available techniques in order to maintain pest populations at levels below those causing economic injury. The concepts behind IPM have evolved since their beginnings in the late 1950s. It is generally agreed that one of the primary objectives is reduced reliance on (especially toxic, broad-spectrum) pesticides and some believe that IPM may (or should) result in reduction or removal of chemical pesticide use. In practice, however, the pesticide industry has remained a profitable (although maturing) business (Figure 1). This indicates that many farmers continue to believe that pesticides are necessary to prevent significant losses in many crops (the largest market), besides which, insecticides continue to be used for control of disease vectors and nuisance pests. Here, I examine some of the reasons for the continued prevalence of pesticides in pest management, and suggest how a more reasoned approach, which accepts the value of pesticides but concentrates on delivering the active ingredients (a.i.s) more effectively, can make a real contribution to pesticide reduction.

Changes in pesticide use are not as easy to quantify as it might seem. During the final two decades of the 20th century, the total value of pesticide sales increased some 2.5 times. This statistic can be misleading because it does not take factors such as inflation into consideration, but average trade weighted growth has been some 1.6% annually. Figures for tonnes of pesticide produced are hardly more useful, since modern pesticides are used at substantially lower rates of application. It would be useful to express sales in terms of hectare dosages, but such data are available only very rarely (a notable exception being in Denmark, see: < http://www.inet.uni2.dk/~iaotb/top20.htm> ). Figure 1 reveals some other significant trends including (a) an increase in the importance of herbicides (mostly at the expense of insecticides) and (b) the present relative unimportance of genetically modified crops (in contrast to their news-worthiness). Figure 2 shows how the regional distribution of pesticide sales has varied over last 20 years. Although Europe and North America continue to account for the largest portion of the market (some 56% combined), there has been nearly a 10% increase in the market share to 36% for Asia and South America (partly in place of eastern Europe), and pesticide use patterns in these regions therefore deserve special attention.

 

Figure 1. Worldwide pesticide (crop protection) markets in the final two decades of the 20th century (data compiled from British Crop Protection Association Annual Reports).

Figure 2. Regional trends in pesticide use (data source as Figure 1).

The term rational pesticide use (RPU) was coined in the title of a book by Brent & Atkin in 1987¹; it can be defined as a focused sub-set of IPM, which attempts to mitigate the adverse effects of pesticide use by improvements in the selectivity of the products themselves and the precision of their application in both space and time. The benefits are maximized with a combination of all three, and the potential benefits include: reduction of costs (for both pesticides and labour), improved safety (especially with insecticides) and reduced environmental impact (through more efficient use of sprays and the use of specific agents).

On a world-wide scale, farmers are likely to be most interested in cost savings, but this will be especially important in the poorest communities. Developing countries presently account for approximately 25% of global agricultural sales values and this proportion is projected to rise. However, not only do agricultural inputs contribute to the debt cycle, but with limited access to protective clothing and medical facilities, cases of pesticide poisoning are more common in developing countries, and have a greater impact on poorer farmers.

Concepts similar to RPU have been promoted elsewhere: all attempt to achieve sustainable agriculture, with a low environmental impact, through a combination of appropriate technologies, but not necessarily excluding the use of pesticides. Examples include: lutte raisonée (supervized control) promoted by the FARRE project in France; `green agriculture' promoted by the Chinese Academy of Agricultural Sciences (together with `white agriculture', that focuses on the use of microbial agents); and `clean production' in Vietnam (where management of pesticides is combined with more careful use of human waste as a fertilizer).

It is beyond the scope of this article to review the many facets of RPU, but it highlights some of the ways in which it can benefit IPM, concentrating in particular on the potential of controlled droplet application (CDA).

Slow Growth of Specifics

There has been a significant trend towards the development of molecules and formulations with lower mammalian toxicity by the major agrochemical companies over the last 30 years. However, with huge development costs, the companies have been under pressure to develop pesticides which have a broad spectrum and thus a wide market, for example neo-nicotinoids and pyrethroids. More specific compounds (even aphicides) by definition occupy smaller proportions of the pesticide market and therefore promise a smaller potential return on research investment. In addition, toxic chemicals (especially organophosphorus compounds such as methamidaphos and monocrotophos) are still widely manufactured and marketed, and alarmingly are still available to unprotected smallholders in some developing countries. More specific compounds are available (e.g. insect growth regulators, fermentation products such as spinosad, and biopesticides) but they tend only to fill `niches' in the pesticide market. Although the need for more specific insecticides is often identified in farmer field schools and by scientists, commercial pressures mean that this does not translate easily to the market place.

Paradoxically therefore, one of the costs of heightened regulatory pressure has been an increased incentive to develop broad-spectrum products that have a large market value, thus possibly increasing the impact of pesticides on nontarget organisms and the environment. The use of broad-spectrum molecules is known to aggravate problems such as pesticide-induced resurgence of relatively unimportant insects and mites. One of best-known examples of this is brown planthopper (Nilaparvata lugens) in tropical rice, which flares-up almost predictably after applications of many pyrethroids. With appropriate cultivation of this crop, it is most straightforward to discourage insecticide use all together, although migratory pests may remain a problem. However, the use of herbicides (for directly seeded rice) and fungicides (against diseases such as sheath blight) is increasing in some countries, and RPU may be able to provide the more complex solutions needed for effective rice protection in such situations.

Between Two Camps

Although good IPM practice comprises the best combination of techniques to manage pests, opinions about the emphasis placed on the various components have become polarized over the last 30 years. Most authorities agree that successful pest management requires a holistic approach that includes cultivation of the crop itself; thus some sections in the Food and Agriculture Organization of the UN (FAO) and other workers with a background in biological control refer to `integrated production and pest management' (IPPM). On the other hand, the Global Crop Protection Forum, representing the major companies wishing to develop both pesticides and genetically modified crops, promotes the term `integrated crop management' (ICM). Unfortunately the protagonists of the two approaches rarely talk to one another, even though there are many similarities between the concepts (their main disagreements are often over essentially socio-economic matters).

Faced with the sustained importance of pesticides, and the absence of specific compounds, RPU provides a means of minimizing use and impact, and this fills a niche in IPM left by pesticide-excluding approaches, yet always attempts to minimize their impact. Scientists, practitioners and policy makers involved in IPM have tended to view any activity associated with pesticides as belonging to the pesticide companies (and preferably to be avoided). In turn the chemical companies (which often provide farmers with most of their information on products) are unlikely to develop or promote techniques that reduce pesticide use (and hence sales). The result is a lack of information and technological development for improving the selection and use of pesticides in a way that will lead to real reductions in use.

Applying Less More Precisely

It is rarely appreciated just how inefficient existing application practices are. In 1977, Graham Bryce pointed out that most conventional insecticide applications as foliar sprays were <0.05% efficient, although (exceptionally) this might reach 6% efficiency for aerial sprays to locust swarms, and herbicide sprays on grass weeds might reach 30% efficiency. Thus, even in the best case, 70% of the pesticide is wasted. Improved application techniques received much attention and extensive research in the 1970s and 80s, but then went out of favour, partly when the commercial potential of genetically modified crops became apparent. With the increased use of herbicides, application research in the 1990s often focused on control of spray drift (not necessarily accompanied by gains in efficiency: see below). Most recently, the concept of `precision spraying' has received attention, which is linked to sophisticated crop monitoring techniques controlled by global positioning systems, and applications are targeted to patches of pests (usually weeds). However, precision spraying has been developed for European and North American conditions and essentially relies on switching conventional atomizers on and off; it does not necessarily address the fundamental inefficiencies resulting from the random nature of liquid break-up by hydraulic pressure.

The concept of controlled droplet application (CDA) is perhaps the ultimate in precision spraying, but it has been disappointingly limited to niche markets. It attempts to maximize dose transfer to a given pest target by the creation of appropriately sized, uniform pesticidal droplets (within practical engineering limits). A number of studies have shown smaller (<150µm) droplets to be more effective for control of arthropod pests and plant diseases than larger ones. Optimization of herbicide use involves a compromise between minimizing drift (by minimizing the volume of spray with droplet sizes of <100µm) but also ensuring that droplets are not so large that they bounce off foliage (an effect that may start to occur if they are >200µm). For a given biological target it is usually possible to estimate the approximate limits of an optimum size band for spray droplets, but more research with individual cases is always desirable. In addition, by targeting sprays better and reducing their number, it may be possible to prolong the life of a.i.s by delaying the development of pest resistance.

CDA uses minimal quantities of a pesticide to maximum effect by improving timing and spatial application, with the additional benefits of reducing off-target contamination and improving work rates. By creating narrow droplet spectra, ultra-low volume (ULV) or very low volume (VLV) application rates can achieve similar (sometimes better) biological results than conventional (hydraulic atomizer) application. Perhaps one of the greatest practical advantages of these low volume techniques involves their capacity to improve work rates; for example, one hectare of cotton might take more than 11 hours to spray at 200 litres/ha (with a conventional knapsack sprayer), but only 4 hours at 10 litres/ha (VLV) or one hour at one litre/ha (ULV). Such improvements in work rate not only reduce labour costs, but also improve timeliness of application in response to monitoring techniques; thus CDA is a very good example of RPU technology.

Early CDA initiatives had only limited success, probably due to a combination of unreliable equipment, insufficient promotion and a perceived need for special formulations. The cause was not helped when the inventor of modern rotary atomizers, Edward Bals, suggested in 1969 that besides ULV rates of application, CDA might achieve `ultra-low dosages'. This idea was obviously an anathema to many chemical companies since it could threaten product sales. However early in the 1980s, ICI (now Zeneca, shortly to become Syngenta) recognised, with the development `Electrodyn' technology, that profitability was not necessarily linked to tonnes of a.i. sold. It recognised that added value might be achieved by incorporating the product in a proprietary delivery system for smallholder farmers. Electrical forces were used to break up the oil-based formulation into very small, very evenly-sized droplets, then to carry and distribute them onto the plant surface. By combining the bottle, formulation and nozzle in a closed, disposable system (the `Bozzle'), operator exposure and application errors could dramatically be reduced by eliminating the mixing and measuring stages and simplifying calibration.

Although technically brilliant, electrostatic spraying in general has failed to make a commercial impact. In the case of the Electrodyn, farmers in some areas were unwilling to commit themselves to the products of just one company, and there has been increased regulatory pressure against the solvents used in formulations (a critical component in the `Bozzle' system). However the rotary atomizer companies survive, and many of the technical problems that constrained widespread adoption of CDA in the early days have now been resolved. With the current heightened awareness of environmental, social and toxicological issues associated with pesticides there is perhaps an opportunity to `rediscover' some of these latent technologies. Provided relatively non hazardous a.i.s are used, CDA spraying, together with other RPU techniques such as banding, baiting, specific granule placement and weed wiping might even ameliorate the currently poor image of pesticides. However, in many circles drift is seen as one of the major problems that pesticide application research has to address.

Drifting Off-Course

Recent changes in policy and practice (especially in Europe and North America) have focused on reduction of spray drift (an issue that has always been important with herbicides). The most common solution has been to develop nozzles that increase droplet size spectra, although this shift takes spray droplet size out of the range demonstrated to be effective for pesticide application. In 1974 Himel distinguished between `exodrift' (transfer of spray out of the target area) and `endodrift', where the droplets fall into the target area but the a.i. does not reach the biological target. Endodrift is volumetrically more significant and may therefore cause greater ecological contamination (e.g. where chemical pesticides pollute ground water). Unfortunately, the policy and regulatory changes that encourage the use of larger droplet sizes in ordinary spray nozzles risk reducing exodrift at the expense of an increase in endodrift. With spray application, it is important to focus on maximizing pesticide delivery to the target, rather than just minimizing drift. Concepts such as controlled drift spraying with narrow droplet size spectra are often critical to the success of low volume application and can achieve efficient dose transfer to the biological target.

Figure 3 illustrates this by showing the droplet size spectra from four different nozzles, juxtaposed to bands indicating the probable optimum size ranges from a biological point of view. Note also that there is a cubic relationship between a droplet's diameter (its `perceived' size) and its volume (proportional to dose). Large droplets that bounce off leaves may still be appropriate for pre-emergence herbicides, but are wasteful in most other circumstances. The same volume of pesticide broken up into smaller droplets could make up a large number of effective doses where plants or insects are the target. The 110-03 flat fan nozzle, often fitted to tractor boom sprayers, is very widely used in western agriculture. At 300 kPa pressure it produces a `medium spray' which includes droplet sizes ranging from those that are too small even to be appropriate for fungicides, to `drops' that are >500 µm. In an attempt to reduce the <100 µm proportion, the same manufacturer produces a `low drift' nozzle with an equivalent output; the proportion <100 µm has been halved to <4%, but this nozzle also produces a wide spectrum of droplet sizes, and the median diameter has been shifted from approximately 150 µm to >300 µm. Compare these spectra with two rotary nozzles: the Ulva+ set for application of water-based insecticide formulations and the `Herbi' designed for spraying herbicides. Using the optimum droplet size criteria, appropriately set rotary atomizers can increase the volume of output in these ranges from <40% to approximately 80%.

 

Figure 3. Droplet size spectra of output from four atomizers spraying water + 0.1% surfactant (Agral 90) measured by a 'Malvern 2600'
particle size analyser.

Rotary atomization is not appropriate for all pest control situations, and hydraulic nozzles are by far the most important means of spraying pesticides. However much could be done to reduce wastage (and operator hazard) with conventional equipment, by better choice and maintenance of equipment. It is interesting to speculate how much of the money spent on pesticides shown in Figure1 could be saved by widespread adoption of improved techniques. If efficiency were to be doubled (eminently feasible from a technical point of view) then RPU could save mankind some US$15 billion annually. Perhaps there is indeed little incentive for pesticide manufacturers to promote improved application techniques.

Getting the Bugs Out

There has been much recent interest in biological pesticides, and the development of delivery systems for microbial agents provides an excellent example of RPU. Biopesticides are among the most specific agents available to the farmer; however, their share in the total pesticide market remains below 1%, and there have often been technical, logistic and commercial difficulties in providing the biological products that have been identified as most appropriate for IPM in some crops. Although widely liked by both ICM and IPPM protagonists, biopesticides will remain primarily subjects for discussion, unless the technical, commercial and conceptual issues can be resolved, so that more products appear on shelves and farmers want to use them.

Amongst perceived constraints are narrow target spectra, poor performance relative to cost, and inconsistent product quality, but a major problem with current use is the poor standard of application to crops, allied with a belief that horizontal transmission mitigates the need for good delivery systems. However, there are studies showing that, as with chemical pesticides, droplet size and coverage affects the efficacy of agents such as Bacillus thuringiensis. Unlike many chemical formulations, biopesticides are necessarily suspensions (as opposed to solutions) and the concept of dose transfer to the target pest in the form of particles must underlie the development of effective delivery. By monitoring efficacy over weeks (rather than days), some biopesticides are substantially more efficacious than their chemical rivals.

This can be illustrated by results gained with the international LUBILOSA Programme.LUtte BIologique contre les LOcustes et les Sauteriaux is a collaborative, multi-disciplinary research and development programme funded by the Governments of Canada (CIDA), the Netherlands (DGIS), Switzerland (SDC) and the UK (DfID). It was set up to develop environmentally friendly biological alternatives to chemical pesticides. Extensive locust spray campaigns in the 1980s caused public concern about the accompanying environmental impact of chemicals, and biological pest management methods are especially important in natural and semi-natural habitats. The programme has developed a mycoinsecticide based on an isolate of the fungus Metarhizium anisopliae var. acridum, which has been field tested against a number of acridid pest species, and is now recognised as an appropriate product for locust control in environmentally sensitive areas. In a recent series of operational trials against Oedaleus senegalensis, it was shown that although the organophosphorus chemical fenitrothion achieves an impressive `knock down', hopper populations recover and two weeks after application a more profound population reduction was achieved in the plots sprayed at ULV rates with Metarhizium conidia. Residues of the fungus were more persistent than fenitrothion but had minimal impact on nontarget organisms - which may have enhanced field efficacy. However, it is not sufficient simply to demonstrate efficacy and register products in this way; there is a continuing need to promote and ensure the continued supplies of good quality, cost effective formulations. It appears that this is presently best achieved by partnership between publicly funded research groups (such as LUBILOSA) and small- to medium-sized commercial companies.

The Challenge

With the increasing supply of cheaper, considerably less toxic and more specific compounds, an open mind is important in providing reliable technical solutions to farmers' problems. Commercial pressures have encouraged the excessive promotion of single technology (`magic bullet') concepts, which have not delivered all that was promised. It is the use of techniques in combination with one another that offers the greatest potential for farmers to reduce costs and impact on nontarget organisms. When it is accepted that pesticidal intervention is indeed occasionally necessary, then RPU could provide a framework for interaction between IPM practitioners and providers of technical solutions. However, we must recognise that:

• In the interests of economic support, quality control and reliability of supply, RPU technologies (such as biopesticides, improved pest monitoring tools and application techniques) are most likely to succeed when provided by commercial concerns, rather than rural communities.
• Alliances are needed between research and development organizations and the small-to medium-scale industries that have the best track record for sustaining RPU technologies.
• It is essential that farmers and other users understand the biological and technical concepts underlying these technologies. The relationship between technology providers (both institutional and commercial) and the needs of farmers is also vital for the successful implementation of RPU and other IPM technologies.
• A re-examination of appropriate environmental and regulatory policies at national and international level would also be most helpful.

RPU is not a new paradigm, but a sub-set of IPM. It recognises that pesticides have been around for more than a generation, and are likely to be around for at least another. Seeing pesticides as dangerous (and conversely biological control as safe) is over-simplistic and sometimes factually wrong. RPU is a mixture of old and new ideas to manage real problems such as pesticide resistance and environmental impact and, of most interest to the farmer, to provide robust but economic pest management.

¹Brent, K.J.; Atkin, R.K. (eds) (1987) Rational pesticide use. Cambridge, UK; Cambridge University Press, 348 pp.

By: Roy Bateman, CABI Bioscience,
UK Centre (Ascot), Silwood Park,
Buckhurst Road, Ascot, SL5 7TA, UK
Email: r.bateman@cabi.org
Fax: +44 1491 829123

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Improving Hot Pepper Production in Jamaica

The Food and Agriculture Organization of the United Nations (FAO) is providing assistance to Jamaica, through a technical cooperation project, to improve production of its famous hot peppers (Capsicum spp.). At present, production and export of hot peppers is one of Jamaica's most important agricultural activities and has been identified as having great potential for development by the Government. The indigenous Jamaican Scotch Bonnet, renowned for its unique characteristics, is one of the best known and most prized of the Caribbean varieties in the export market. Over J$38 million (US$1.0 million) per annum are currently earned from the industry and more than 3000 people are directly or indirectly employed in it.

Maximizing production and hence returns from the crop are constrained by a number of factors, the chief of which are a shortage of good quality seed and the impact of various pests. The most important arthropod pests are gall midges (Contarinia lycopersici and Prodiplosis longifila), the broad mite (Polyphagotarsonemus latus) and aphids (Aphis gossypii and Myzus persicae). However, the gall midges constitute the most pressing problem, because they are considered pests of quarantine significance in the USA, which is a major market for the crop. Effective control measures need to be implemented urgently. At present, farmers rely heavily on chemical pest control methods - indeed, it is likely that the gall midge problem could be pesticide induced.

The FAO project, which was initiated in April 2000, aims to assist the Government of Jamaica with its hot pepper seed development programme, and amongst its objectives is the implementation of an IPM strategy for effective control of gall midges and broad mite. A number of preliminary activities have been initiated within the IPM programme so far. These include: identification of demonstration farmers' plots, installation of equipment, identification of laboratory facilities at Bodles Research Station, development of protocols for pesticide trials, looking at the role of indigenous natural enemies and preliminary laboratory studies on pest biology and their natural enemies. The Caribbean Agricultural Research and Development Institute (CARDI) has also been undertaking studies on both the hot pepper pests in question.

Farmer participatory research and training is also a key element of the FAO project. Towards this end, a national training workshop on farmer participatory approaches was undertaken in August 2000 where 15 extension workers were trained to develop and implement a farmer participatory IPM programme in six parishes in Jamaica. One concrete outcome of the workshop was progress in the development of a proposed curriculum framework for farmer training in hot pepper production techniques in which participatory IPM will be a major component.

Source: Pollard, G. (2000) FAO Assistance to Jamaica for improving hot pepper production, in part through development of an IPM programme for gall midges and broad mite. CaribbeanIPM Knowledge Network, Current Awareness Bulletin, No. 2 (September 2000).

By: Gene V. Pollard,
Regional Plant Protection Officer,
FAO Sub-Regional Office for the
Caribbean, P.O. Box 631-C, Bridgetown, Barbados, West Indies
Email: Gene.Pollard@fao.org
Fax: +1 246 427 6075
and
Lennox Chandler, FAO TCDC
Consultant, Ministry of Agriculture and Rural Development, P.O. Box 505, Graeme Hall, Barbados, West Indies
Email: lennoxchandler@excite.com
Fax: +1 246 420 8444

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