Invasives Blog

The yield losses attributed to Asian citrus greening disease once established can be devastating. If the disease continues to spread unabated in the citrus growing regions of East Africa,  the annual value of lost production could potentially reach up to US$127 million over the next ten to 15 years, according to a recent paper published by CABI.

The paper, The Asian Citrus Greening Disease (Huanglongbing): Evidence Note on Invasiveness and Potential Economic Impacts for East Africa, provides a review of the global literature on Asian citrus disease or huanglongbing (HLB) and estimates its potential economic impact on East Africa. The paper also makes recommendations for biosecurity preparedness, surveillance and management options to help decision-makers and citrus growers.

Destructive disease

A bacterial disease spread by infected sap-sucking insect pests, Asian citrus greening is arguably the most devastating citrus disease worldwide. Originating in Asia, it has spread globally through trade and now poses a huge economic threat to nearly all citrus-producing regions around the world.

The primary vector and transmitter of HLB, the Asian citrus psyllid (Diaphorina citri) has recently been detected in Kenya and Tanzania. The HLB bacterium has also become more widespread in the region, meaning there is a high risk of proliferation. This is a serious concern for citrus producers in these and neighbouring countries.

Importance of citrus

Citrus is one of the world’s major fruit crops, recognized for contributing to food and nutritional security, and ranks first in the global fruit trade. In 2018, around 139 million tonnes of citrus were produced globally. In East Africa, where citrus is a key crop for smallholder farmers, an average of 1.2 million tonnes were produced in 2018.

With this in mind, Asian citrus greening disease now poses a serious threat to small-scale farmers’ livelihoods. Fruit from disease-ridden trees are bitter, small, and drop prematurely, making them unsellable and ultimately, HLB can lead to the premature death of trees. As a result, orchards infected with Asian citrus greening can become economically unviable within 7 to 10 years of planting.

Economic impact

As the HLB invasion in Africa is in its early stages, only minimal analysis of losses is available from the literature. However, the authors underline that, as infected plants age and the disease spreads, the losses to citriculture across the continent could become substantial.

Basing figures on losses from HLB in Florida, where production continues to be jeopardised by the disease despite collective management practices, the paper estimates the annual value of lost production in Ethiopia, Kenya, Tanzania, and Uganda will likely be between US$21.3 and 63.8 million within five to ten years. This increases to between US$63.8 and 127.6 million over ten to 15 years. This underlines the pressing need for rigorous and practical action plans for vulnerable citrus-producing regions.

Recommendations

The paper aims to provide a review of management from global experiences, as well as consolidating relevant research to provide recommendations for decision-makers in Africa.

These recommendations are particularly geared towards those accountable for the response to the insect vector and disease, as well as for external organizations seeking to assist in management.

The first step is to recognise the urgency of the situation and the magnitude of the threat Asian citrus greening disease presents. Any response to managing the wider introduction and spread of the disease will require cooperation across many sectors including government officials, regulatory agencies, research institutions and farmers.

Raising Awareness of Asian citrus greening disease

For Kenyan citrus farmers, Asian citrus greening is still a new disease with information on identification,  monitoring and mitigation limited.

The paper highlights the need to raise awareness of the disease and the threat it poses among farmers, extension agents and quarantine workers, and to learn from experiences in other affected countries to help limit spread and coordinate and harmonise management across the region. This could be through media campaigns, training, and communication materials in local languages. What’s more, these recommendations must be safe, sustainable, available, and affordable to the local communities in order to ensure uptake.

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Read the full paper: The Asian Citrus Greening Disease (Huanglongbing): Evidence Note on Invasiveness and Potential Economic Impacts for East Africa

Invasive Species Compendium (ISC)

Asian citrus greening disease ISC: https://www.cabi.org/isc/datasheet/16565

Asian citrus psyllid ISC: https://www.cabi.org/isc/datasheet/18615

African citrus greening disease ISC: https://www.cabi.org/isc/datasheet/16564

https://www.cabi.org/news-article/cabi-shares-expertise-on-how-to-tackle-citrus-greening-disease-in-the-caribbean/