|The Courier N° 145 - May - June 1994- Dossier : European Union: the Way forward - Country Report: Ethiopia (EC Courier, 1994, 104 p.)|
by Don Walmsley
The answer to farmers' pest problems seemed to have been found in the late 1940s and early 1950s when synthetic pesticides became available in vast quantities in the industrialised countries of the world. In time these came into general use in the Third World countries. Not only were farmers there introduced to the new technologies through government extension services; they were also enthusiastically encouraged to adopt these practices by the representatives of the agro-chemical manufacturing companies - for obvious reasons. Generally, farmers who could afford to buy them were impressed by their obvious effectiveness in wiping out the pests and thus reducing crop losses.
Unfortunately, as is now well known, this happy state of affairs did not last for very long. Soon insect pests developed resistance to the chemicals with subsequent resurgence. The situation was made worse since often the chemicals used not only destroyed the target pest but also its natural enemies, thus upsetting the ecological balance in a negative way. The immediate answer to this was to apply heavier doses and develop new active ingredients. However, it soon became clear that this cyclic approach could not be maintained successfully on an ongoing basis. A new strategy was needed.
Thus, in the 1960s other concepts were developed whereby a total eradication of the target pests was not expected but rather that they be kept at acceptable levels through a set of management practices which might, or might not, include the use of chemical pesticides. This type of approach became known first as integrated pest control (IPC) and later, as the concept developed, as integrated pest management or IPM.
The Caribbean situation
Farmers in the Caribbean region, in common with those in other developing countries, have been using chemical pesticides in ever increasing quantities and, variety of products. They became familiar with the application techniques and were encouraged in their efforts by the agro-chemical suppliers and government agencies. Many governments, in their desire to assist agricultural development, introduced subsidy schemes for agricultural inputs. These often included pesticides, thus exacerbating the potential for their over-use.
In more recent times there has been the realisation that apart from the more costly inputs, there were other prices to pay for the indiscriminate use of these potentially dangerous agro-chemicals. These include the health hazard, not only to the farmers themselves but also to the general population, and the deterioration of the environment. There are also economic considerations which cannot be ignored. Several Caribbean producers and exporters of fresh fruits and vegetables have found out to their cost that consumers in importing countries are not willing to tolerate chemical residues in their foodstuffs and have a very strict monitoring system. Also there are likely to be losses in the newly developing ecotourism business if potential visitors have doubts about the quality of the local food and environment. Many of the Caribbean countries depend heavily on agricultural exports and tourism in their economy so in this context perhaps the proper question should be: can the Caribbean countries afford not to reduce pesticide use and adopt the more environmentally friendly IPM approach?
Major pest problems
Among the most serious pests in the Caribbean are the sweet potato whitefly, (Bemisia tabaci) and Thrips pa/mi. These two pests are usually found together and any strategy for their control has to deal with them as a complex. Both are mainly pests of annual vegetable crops, both are virus vectors, and both are believed to have assumed their present pest status as a result of the insecticide regimes currently practiced.
Thrips palmi was first recorded in the Caribbean in 1985. It has been estimated that its establishment on solanaceous and curcubitaceous crops has contributed to trade reductions of over 90% in both Guadeloupe and Trinidad. In addition, local markets can only offer smaller, deformed and scarred fruit.
During the mid-1980s a new strain of the sweet potato whitefly (sometimes referred to as silverleaf whitefly) invaded the Caribbean and is now devastating important root and vegetable crops. The diseases associated with whitefly which predominate in the Caribbean are caused by geminiviruses. Whiteflies and the diseases they transmit cause epidemics resulting in annual losses costing millions of dollars.
Another cause of great concern is the citrus tristeza virus (CTV). It was introduced with its vector, the brown citrus aphid (Toxoptera citricidus), from South Africa into South America in the early part of the century, causing havoc to the citrus industry in much of Argentina, Brazil and Uruguay over the period between 1930 and 1960. More recently, outbreaks in Venezuela in the early 1980s have devastated the industry there. Since then the vector has been spreading steadily northwards and has been found in Central America, reaching Nicaragua by the middle of 1993 - its arrival in Belize is considered imminent. CTV has already been widely distributed in the Caribbean through movement of budding, grafting and planting material. Trees with sweet orange rootstocks are not severely affected but fruit on sour orange stocks is very susceptible and these are still the most common in the Caribbean. Spread is currently low because of the low transmission efficiency of the endemic vector species and there is a preponderance of the mild strain of the virus. This situation will change dramatically if no action is taken before the inevitable arrival of Toxoptera citricidus.
Also of much concern to citrus growers in the region is the damage done by various citrus root weevils - for example, in the Dominican Republic Diaprepes abbreviatus is considered a major pest.
The seminar on IPM held in the Dominican Republic
It was within this scenario that for the recent (November 1993) CTA/ CARDI ninth annual Caribbean seminar the topic chosen was IPM: A Comprehensive Strategy for the Caribbean Farmer. The meeting was held in Santo Domingo, the capital of the Dominican Republic, one of the most recent countries to attain membership of the ACP-EU grouping. The seminar was jointly organised by CTA, the Caribbean Agricultural Research and Development Institute (CARDI), the Secretaria de Estado de Agricultura and its Departmento de Investigaciones Agropecuarias (SEA/DIA), the Fundacion de Desarrollo Agropecuario Inc. (FDA), the Junta Agroempresarial Dominicana Inc. (JAD), and the local office of the Instituto Interamericano de Cooperacion pare la Agricultura (IICA).
The theme was particularly appropriate for the Dominican Republic since the once thriving tomato industry has recently suffered severe losses as a result of whitefly infestation, and the citrus industry is severely affected by root weevils and under threat from CTV and its vector, Toxoptera citricidus. Indeed, the subject of the meeting was considered of such importance there that the Secretary for Agriculture, Victor Hugo Hernez, not only formally opened the seminar but also participated in the closing session.
The technical papers presented by scientists - from the region and other parts of the world - revealed that one of the main constraints introducing the IPM approach was the difficulty in persuading farmers of its value and long-term effectiveness. They were used to applying pesticides and seeing their obvious and immediate results. Therefore one of the main tasks would be to educate farmers as to the advantages of reducing pesticide use and adopting the more sustainable management practices now advocated.
In this respect, it was suggested at the meeting that a successful model which could be adapted to dealing with serious pest problems in the Caribbean was that developed under a FAO programme on rice in south-east Asia. In that part of the world problems arose because the new, improved rice variety which had been planted over very large areas was found to be susceptible to the rice brown planthopper, previously only reported to be a pest of rice grown in temperate countries. The pest quickly developed resistance to insecticides and its other characteristics, along with the destruction of its natural enemies, led to outbreaks of epidemic proportions. Research into the whole pest complex and ecology of the system eventually came up with the recommendation that the use of pesticides should be discontinued. The problem now was to get this message across to the extension agencies and, most importantly, the farmers. A massive IPM programme was mounted to sensitise farmers to the role of natural enemies in pest regulation. This was based on 'IPM Farmers Field Schools', which is a new methodology entailing a continuing close collaboration between researchers, extension workers and farmers. The method involves elements of infield training and hands-on experience. Eventually, farmers can decide what action to take themselves without having to seek advice from others. Part of the strategy is that farmers train other farmers. Three basic principles followed by the farmers are: grow a healthy crop; conserve beneficial organisms such as pest predators and parasites; and observe fields regularly to determine the management actions necessary to produce a profitable crop.
The components of an appropriate pest management regime could include: resistant plant varieties; biological control (predators, parasites, pathogens, 'biopesticides'); crop sanitation (burning residues, closed season); mechanical methods (colour traps, mulches); cultural practices (crop rotation, cropping mix, overhead irrigation); pheromone technology; judicious use of selective, less deleterious chemicals (including natural products and insect growth regulators) along with efficient spray application techniques; plant quarantine.
Research on most if not all of these elements was reported from several countries in the Caribbean but seldom had it been possible to offer farmers a complete package of IPM practices tailored to their own particular circumstances. Some examples of the use of such components are discussed below.
Farmers in Barbados have become more selective in their use of insecticides and now also include insect growth regulators. In Trinidad a range of indigenous natural enemies of Thrips palmi have been recorded, including predatory mites, anthocorid bugs and fungi, and research is now aimed at mass production of these for field application. A promising fungus species for control of both whitefly and T. palmi was found to be Paecilomyces fumosoroseus. This pathogen, which also infects diamond-back moth, is being fieldtested in aqueous and oil-based formulations. In the hope of containing whitefly and associated viral diseases, the Dominican Republic has enacted laws and regulations to enforce a closed season and to regulate planting of whitefly host crops in selected regions. Other components of alternate management strategies to conventional pesticide use tried there include intercropping vegetables with sorghum, use of neem extracts and insect growth regulators, and resistant tomato varieties. In Honduras, several types of control methods (mechanical, cultural and chemical) for geminiviruses in tomato and chile peppers have been investigated. The most effective were protected nurseries, optimal cultivation practices, and efficient insecticides. In the Dominican Republic the fungus Beauveria bassiana and the insect Tetrastichus haitiensis are being mass-produced for use in the fight against the citrus root weevil, Diaprepes abbreviatus.
In response to the threat to the citrus industry posed by the severe strains of tristeza along with its very efficient transmission by T. citricidus, most countries (including Trinidad, Belize, Martinique and Guadeloupe) are changing the susceptible sour orange rootstock used in their citrus nurseries to more resistant varieties (which should also be tolerant to other major diseases) and persuading farmers to plant them as a matter of urgency. The bud wood used must be certified free of transmittable diseases. Eradication of trees with severe CTV strains is another important but unpopular measure Cross protection techniques using mild strains of CTV are also being considered. More stringent quarantine controls are being put into effect.
On the field excursion, seminar participants were able to see at first hand the way in which farmers in the Dominican Republic were adopting IPM technology. By using these measures, vegetable farmers in the Valle de Constanza have been able to reduce the number of spray applications, for example, from 9-12 to 3-5 for a cabbage crop, and from 10-12 to 4-5 for tomato; sweet potato spraying has been cut out altogether from a previous 23 sprays per crop. It is implicit in this that some monitoring mechanism of the pest population be established in order to give guidelines on when it would be necessary to apply chemical pesticides. Here, farmers were using pheromone and colour traps to assist in the monitoring process. However, the difficulty of getting over to farmers that the chemicals they were using posed a health hazard was clearly demonstrated; farmers were spraying without safety equipment and children were playing nearby!
It was interesting to note that a pesticide manufacturer was actively assisting in this programme - the attitude being that in the future only pesticides compatible with the IPM concept would be acceptable.
The participants devided into four working groups to discuss: IPM for vegetable crops; IPM for citrus; IPM for small-scale farmers in mixed systems; institutional methods to promote IPM. The main conclusions and recommendations may be summarised as follows:
· Policy-makers in the region should be made aware of the concept and importance of IPM to agricultural development consistent with a healthy and stable environment
· Noting that the International Pest Management Working Group intends to launch a Latin American and Caribbean sub-group at its 1994 meeting in Costa Rica, steps should be taken to have the recommendations arising from this present meeting placed before the sub-group for endorsement. Also steps should be taken to establish a Caribbean chapter of the subgroup with its own newsletter.
For citrus, the status of proposals for international and regional cooperation (FAO and IACNET) needs to be clarified. The conclusions of this meeting will be presented at a CTV workshop in Mexico at which international cooperation and funding will be considered. It is essential that a system of regional cooperation in transfer of information, budwood and technology be established. The offer of safe citrus germplasm transfer to the region through Martinique by the French Inter-ministerial Fund for Regional Cooperation, with approval from the International Board for Plant Genetic Resources, was noted.
· There is an urgent need for the education/training of farmers and extension workers to bring about a change in attitude and to give them the required knowledge in the appropriate use of recognised IPM components in local farming systems. This would involve working with farmers and farmer organisations using succesfful models developed elsewhere and adapted to Caribbean conditions.
· A group should be set up with responsibility for producing hand-outs/factsheets on the several approaches recognised at the meeting for the control of Bemisia, thrips, tristeza and Diaprepes. These should be addressed to farmers, extension workers and researchers and be made available in the three main languages of the Caribbean - Spanish, English and French. The support of CTA, CABI etc. for this exercise should be sought
· A study of economic losses incurred in the region due to pest damage is needed along with the establishment of economic thresholds.
· An inventor of the regional physical and human resources available for IPM should be developed along with a database on all aspects of IPM.
· Plant quarantine should be strengthened (possibly with the assistance of FAO).
· Increased control of pesticide use should be implemented through updating legislation and regulations at the national level.
· Coordination of research activities is needed among universities, government institutions and other research organisations. Networks for research and information should be established with links to international groups.
· Although there is a need for support from the international donor group, it is very important that budgeter support is provided at the national and regional levels. D.W.
The author is indebted for background material to papers read at the seminar by T J Perfect and J C van Lenteren.