FAO Regional Office for Latin America and the Caribbean

Transboundary pests and diseases are characterized by their high capacity and speed of migration from infected/infested zones to previously free zones, thereby spreading rapidly between countries. Moreover, emerging pests and diseases are in a process of the early incidence; so although it is potentially possible to influence their definitive establishment in different areas, at this stage the best strategies and methodologies for their prevention and mitigation are generally unknown.

One of the main emerging transboundary pests to have appeared in the last few years in Latin America and the Caribbean is HLB. Since it was first reported in 2004 in Brazil, this disease has spread to 12 countries of the region.

Regional management of Huanglongbing (HLB) in Latin America and the Caribbean

Emerging transboundary pests and diseases

Emerging transboundary pests and diseases pose a serious threat to agriculture in Latin American and Caribbean countries, since the characteristics of threats of this type mean that farmers and institutions have little response capacity and are only in a position to react when the problem has already grown to major proportions and most of the damage can no longer be avoided.

Although pests of this type affect farming on all scales and of all types, in most cases it is small-scale family farmers who are hit hardest and have their livelihoods compromised, since higher production costs and/or changes to their productive systems are generally harder for them to absorb.

In this situation, the main strategy for managing transboundary pests and diseases is prevention and effective vigilance. Nonetheless, prevention implies a learning curve that often hinders timely reaction. This provides an opportunity to address the problem of emerging transboundary pests and diseases based on a regional strategy that draws on experiences and lessons learned.

Citrus Huanglongbing (HLB)

One of the main emerging transboundary pests to have appeared in recent years in Latin America and the Caribbean is HLB. Since it was first reported in 2004 in the Brazilian state of São Paulo, the disease has spread to 12 of the region's countries.

HLB attacks various plant species of the citrus genus. Originating in Asia, it is currently considered the most devastating citrus disease worldwide, owing to the damage it causes, the difficulty of diagnosing it, and the speed at which it spreads.

The common names of the disease are "HLB", "Huanglongbing", "citrus greening disease" or "yellow dragon disease". The causal agent of HLB is a Gram negative, vascular, phloem-restricted bacterium of the Candidatus Liberibacter genus, which is transmitted by insect vectors. Three species are currently known: Candidatus Liberibacter asiaticus, Candidatus Liberibacter africanus and Candidatus Liberibacter americanus. Only those of Asian and American origin can be found in the region.

The HLB causal agent is mainly dispersed by two vectors: Diaphorina citri (Kuwayama) in the case of the Asian and American species, and Trioza erytreae (Del Guercio) for the African species. Only Diaphorina citri is present in the region.

HLB is also a disease that attacks all commercial citrus species and other species of the Rutaceae family. It severely affects orange (Citrus sinensis), mandarin (Citrus reticulata) and bitter citrus fruits, such as Mexican lime (Citrus aurantifolia) and Persian lime (Citrus latifolia). Nonetheless, many other citrus species can also display varying degrees of symptoms.

HLB dissemination factors in space and time

As the figure shows, HLB and its spatial and temporal dissemination results from a complex interaction between the host (the citrus plant), the associated pathogen (bacterium), the vector that transmits it (Diaphorina citri in Latin America and the Caribbean), and the environment (mainly climatic factors). The latter increase or reduce the disease's incidence probabilities according to the climate's effect on the biology and interactions between hosts, vectors and causal agent.

The disease, and the cost of managing it, generate direct losses in the yield, volume and value of production, with negative economic, social and environmental consequences. The economic impact of HLB stems from the importance of the hosts, which include all commercial citrus species. The "economic death" of the plant occurs gradually following infection by the pathogen, owing to defoliation, deformation, and fruit drop, with a consequent reduction in their commercial value, and its eventual biological death. For this reason, and given the lack of efficient management methods, the disease is estimated to have killed over 60 million trees worldwide (10 million in Brazil alone) causing crop losses of up to 100% in countries such as South Africa.

Moreover, taking the case of Florida in United States as an example, HLB has raised production costs by up to 50%. In Mexico, in the first year since HLB was detected, the disease reduced the yield of infected trees by up to 50%; and it is estimated that, within five years, under a high-impact scenario, the potential losses in producer zones would be about 3 million tonnes, equivalent to 41% of the country's total production.

As a result of these losses, in some countries, for example in Africa and Asia, citrus cultivation has been relocated to prosper in places that are unsuitable for development of the vector (Africa and Asia) and/or the pathogen (Africa).

The rise in production costs means that small- and medium-sized producers, who are less technically advanced and have less capital, become vulnerable to economic losses and are the hardest hit by HLB.

The reduction and loss of citrus production directly affects employment, both in the countryside and in agribusiness, and also in firms involved in the production, processing and distribution of citrus fruits.

In addition to this there are environmental impacts associated mainly with the elimination and burning of millions of trees and intensive use of chemical pesticides.

The regional HLB prevention and mitigation strategy

In this context, FAO is working with the countries of Latin America and the Caribbean to implement a regional strategy to support the sustainability of regional citrus cultivation to benefit the wider agricultural sector, particularly in highly vulnerable zones. To that end, FAO has fostered cooperation between countries through various initiatives and projects, aimed at making the most of the experience of countries that already have instruments in place and personnel trained for the regional management of the disease.

One of the premises of this cooperation between countries is that the current status of the disease, and its risk, require a regional strategy to develop a coordinated and vigorous defence to control this epiphyte, since isolated programmes run the risk of providing an ineffective resistance. There would also be a worry that countries that are poorly equipped to manage the disease might become inoculum reservoirs, thereby posing a permanent risk for managing HLB in the region and threatening the sustainability of citrus cultivation.

The regional strategy involves implementing a number of measures and actions that are integrated and coordinated at the local, national, subregional and regional levels, with the following goals:

  • Reduce the sources and burden of inoculum, effectively and quickly.
  • Reduce the population of infective psyllids in geographic areas that are already infected.
  • Reduce the risk of infestations by external psyllids populations that migrate from one geographic area to another uninfested one.

As an initial step towards achieving these goals, a Regional Committee of Experts was set up, comprising researchers, staff and technical experts with wide experience in HLB management, both from the technical standpoint and in terms of human capital organization at the national level. The Committee includes experts from Belize, Brazil, Chile, Jamaica and Mexico, with strengths in different areas of knowledge linked to HLB management.

As a result of the work of the FAO Technical Group and the Regional Committee of Experts, the following technical guidelines for activating the strategy at the national, subregional and regional levels are available to the countries of the region:

  • Strategic Framework for the Regional Management of HLB in Latin America and the Caribbean
  • National Framework Plan of Action for the Regional Management of HLB
  • HLB management protocols, including adaptations of protocols already developed by national and subregional institutions.

Towards the construction of a regional strategy for managing transboundary pests and diseases

Based on experience and lessons learned in implementing regional HLB management, FAO envisages the opportunity to use a regional approach in the management of other emerging transboundary pests and diseases, allowing for a coordinated and vigorous defence to control the corresponding epiphytes.

Components of a regional strategy for managing transboundary pests and diseases

As in the case of HLB, from the operational standpoint, the regional management of any emerging transboundary pest involves a large contingent of activities and interactions occurring at different territorial levels of action. These interactions should be seen as the pathways linking those who participate in regional management, but with emphasis on the public sector, since it is best placed to facilitate the flow of information and actions that help to make the potential advantages of regional management effective.

The regional management of HLB and its different lines of action involves participation by multiple actors (public and private), who play different roles and have special access to different types of resources to achieve the goals of regional HLB management. These include Regional Plant Protection Organizations (RPPOs), National Plant Protection Organizations (NPPOs) and the growers themselves, who ultimately are the key agents of vigilance, prevention and mitigation.

In short, a regional strategy for the management of transboundary pests and diseases should include four interrelated components:

  • Dynamic information systems
  • Harmonized norms and standards
  • Identification of current HLB management measures
  • Development of institutional capacities

These components should be implemented at three levels: national, subregional and regional, as shown in the figure above.

The role of FAO in the regional management of HLB

FAO's role is to facilitate the process of implementing a regional management strategy, as it has been doing in the case of HLB; while at the same time promoting cooperation between countries based on their experiences and lessons learned.

For that purpose, FAO highlights the role of the Regional Committee of Experts as a key tool that has been fundamental to the success of regional management in the case of HLB. The experts on the Regional Committee are identified by the countries themselves and constitute the cooperation base, which ultimately is what makes it possible to implement a regional strategy. In collaboration with the Regional Committee of Experts, FAO proposes strategic guidelines to the countries based on experiences that already exist on the management of emerging transboundary pests.

In all of the aspects mentioned, it is important to stress the need to develop strategies for the regional management of emerging transboundary pests as part of rural development policies with a territorial focus, which include overall resource needs and activities beyond the traditional sector approach, and which are aligned with the Sustainable Crop Production Intensification (SCPI) approach proposed by FAO.