Citrus farmers of Mzansi have been warned to take note of the Asian citrus greening disease, which poses a serious threat to the global citrus industry.
Also known as Huanglongbing (HLB), it is caused by the bacteria pathogen, Candidatutus Liberibacter asiaticus, an insect vector-transmitted by the Asian citrus psyllid (ACP), Diaphorina citri.
The citrus killer may not be present in Mzansi as yet, but Asian citrus greening poses a serious threat to the citrus production in South Africa, the Southern African Development Community (SADC) and the African continent.
Signs and symptoms
Symptoms on leaves and citrus shoots include yellow shoots, asymmetric, mottled leaves, small upright chlorotic leaves, out of phase flushing and branch dieback.
Flower and fruit symptoms include unseasonal and heavy flowering on diseased branches, small, lopsided, bitter-tasting fruit with small, brown, aborted seeds and uneven colouring at maturity and excessive fruit drop.
In the African continent, this specific strain has already been detected in Ethiopia and Kenya and the insect vector has been detected in Kenya and Tanzania.
In a media statement, ministerial spokesperson Reggie Ngcobo warns, “The sooty mould growth resulting from excess honeydew production can also affect the plants’ ability to photosynthesise, which can affect overall plant health.
“It is the most devastating disease of citrus worldwide, causing serious yield losses to producers in countries where it currently occurs.”
Disease threatens food security
If the disease and its primary vector were to be detected, infected citrus trees will not produce edible fruit, decline in numbers, and die. This, Ngcobo, will be a point of, “Major concern for food security and the loss of market access due to a major loss in the production of required fruit volumes.”
Farmers, nurseries, international travellers, importers, researchers, and members have been called to strictly adhere to the country’s phytosanitary regulatory framework.
The department, in collaboration with the citrus industry, has established an HLB steering committee. They, in turn, developed an action plan to minimise the risks of introduction of HLB and ACP in South Africa.
In February, minister Thoko Didiza approved and published the relevant control measures in the Government Gazette in accordance with the provisions of the Agricultural Pests Act, 1983 (act number 36 of 1983).
Importers of plants and plant products must also follow all the proper import procedures in terms of the act to help minimise the introduction, establishment and spread of any potential harmful species in the country.
“This will minimise the introduction, establishment and spread of this disease in South Africa and the SADC region,” said the department of agriculture, land reform and rural development.
“The introduction of this disease in the SADC region will have devastating consequences for the citrus industry, which is already under immense pressure, dealing with other economically important pests and diseases, such as Citrus black spot, False codling moth and fruit flies.
Take precautionary measures now
It is imperative that all role players involved in the citrus industry observe all precautionary measures in terms of the relevant legislative prescripts to help minimise the risks of introduction of Asian citrus greening and its primary vector Asian citrus psyllid into South Africa.
Ngcobo said that these regulatory interventions were in place to ensure preparedness and response to any possible introduction, establishment and spread of this disease. Departmental officials have met with their counterparts in Kenya, to map a way forward on how to with HLB and ACP in Kenya and to minimise its introduction into Southern Africa.
A national survey to enhance the chances for early detection of the disease as well as the vector forms part of the strategic plan of the department of agriculture, land reform and rural development.