Citrus greening disease is one of the most serious threats to citrus crops worldwide today. This bacterial infection causes considerable damage in orchards, where it affects fruit production and quality and causes tree death. What are the causes of this disease? How can it be identified? And what control measures should be adopted? Explanations.
What is Citrus greening disease ?
Citrus greening disease, also known scientifically as Huanglongbing (HLB) or Citrus Greening , is an extremely destructive bacterial infection that affects citrus fruits. It is caused by the bacterium Candidatus Liberibacter , divided into three subspecies: L. c. asiaticus , predominant in Asia, L. c. americanus , localized in America, and L. c. africanus , identified in Africa.
First detected in China in 1919, this disease has rapidly spread throughout tropical and subtropical areas of the globe. Today, it is prevalent in Southeast Asia, North and South America, the Caribbean, and Africa. Although currently absent from Europe, a less virulent version was identified in 2019 in northern Spain and Portugal. Overseas, active outbreaks have been reported in the Antilles, Reunion Island, and more recently in Guyana in 2022.
All species of Citrus , whether oranges, lemons or grapefruit, are susceptible to this disease. It also affects some ornamental trees and shrubs of the Rutaceae family, broadening its threat spectrum.
To date, Huanglongbing poses a major challenge to citrus crops, compromising both productivity and fruit quality.
Need a solution for Citrus greening disease?
Modes of transmission
Citrus greening disease is spread primarily by psyllids , piercing-sucking insects that feed on the sap of citrus trees. Two major species are involved in this transmission: the Asian citrus psyllid ( Diaphorina citri ) and the African psyllid ( Trioza erytreae ) , the latter of which has already been detected in Europe. By biting the trees to feed, these insects infect the sap-conducting tissues with the bacterium Candidatus Liberibacter , causing the disease to appear.
Psyllids, in addition to transmitting the bacteria, excrete a honeydew that promotes the development of sooty mold, a black mold that further weakens contaminated plants. Their presence is exacerbated in areas with warm climatic conditions , conducive to their proliferation.
Another important vector of spread is the transport of infected plants or contaminated grafts. This practice, often carried out without rigorous controls, accelerates the introduction of the disease into new regions, complicating prevention and management efforts.
What are the symptoms of the disease?
The first signs of the disease are often difficult to detect , as they appear several months after contamination.
On the leaves
- The leaves show irregular yellowing and mottling.
- The growth of young leaves is slowed.
- Premature leaf drop may occur.
On fruits
- The fruits are deformed and reduced in size.
- A partial or reverse coloration is observed, with a green base and an orange top.
- Their taste becomes bitter and acidic, making them inedible.
- Premature fruit drop directly impacts harvests.
On the tree
- The branches gradually die off.
- The growth of the tree is slowed.
- The decline in vigor eventually causes the tree to die.
Impact of the disease
Citrus greening disease has a devastating impact on citrus orchards. It leads to massive yield losses . Fruit from infected trees is often unsaleable, and growers suffer major economic losses.
In some regions, citrus cultivation has even been abandoned in favor of other, less vulnerable crops.
For consumers, these disruptions translate into reduced supply, higher prices, and increased dependence on imports from regions that have not yet been affected.
Prevention and control of Citrus greening disease
Prevention of Citrus greening disease relies on rigorous measures to limit the spread of the bacteria. In Europe, strict restrictions prohibit the import of Citrus plants intended for planting, in order to avoid the introduction of contaminated plants.
Infected trees should be removed promptly to reduce the risk of transmission to surrounding crops.
Increased vigilance is necessary to detect the first symptoms of the disease , whether on the leaves, the fruits or the tree as a whole.
The fight against psyllids , the main vectors of the bacteria, also represents an essential axis.
Agrobiotop solutions against Citrus greening disease
At Agrobiotop, we develop solutions that strengthen plants and crops against various issues such as Citrus Greening. We recommend biostimulants such as:
- YAKASELF
- CHITOPROTECT (base substance – Elicitor)
Are you experiencing this problem on your citrus crops? Do not hesitate to consult us on the solutions to put forward on this disease and against Psyllus pests.
