Yellow Dragon Disease (YD): Symptoms, Transmission, Prevention and Control

Yellow dragon disease , also known as Huanglongbing (HLB) or citrus greening , is one of the most serious bacterial diseases affecting citrus trees. Caused by the bacterium Candidatus Liberibacter , this devastating disease reduces the lifespan, productivity and quality of citrus trees, particularly affecting orange , mandarin and grapefruit trees . At Agrumiverse , your citrus plant supplier , we help you understand and prevent this threat to protect your crops.

Symptoms of HLB

Symptoms of HLB vary depending on the citrus species and the stage of the disease, but here are the most common:

On the leaves:

• Asymmetrical yellowing: One part of the leaf turns yellow while the other remains green.
• Discolorations along the veins: Appearance of yellow mottling or asymmetrical discolorations along the veins.
• Yellowing of leaves by branch: Affected branches show progressive yellowing.

On fruits:

• Deformation and abnormal coloring: Fruits become small, hard and deformed, with irregular coloring.

On the tree:

• Progressive decline: The infected tree suffers a general weakening which can lead to its death.
• Premature leaf and fruit drop: Trees lose their leaves and fruit before maturity, reducing production.

Trees infected with HLB are also more vulnerable to other diseases and environmental stresses, which exacerbate their decline.

Transmission of Yellow Dragon Disease

Yellow dragon disease is primarily transmitted by insect vectors, the main one being the Asian citrus psyllid ( Diaphorina citri ). This small insect feeds on the sap of citrus trees and transmits the bacteria as it migrates from tree to tree.

Citrus Species Affected by HLB

HLB can infect most citrus species and cultivars, as well as some of their close relatives. The most susceptible species are:

Very sensitive species:

• Sweet oranges
• Mandarins and mandarin hybrids (tangelos)

Moderately sensitive species:

• Grapefruits
• Lemons
• Bitter oranges

Less sensitive species:

• Limes
• Kumquats

Although HLB is currently absent from the Mediterranean basin, it remains a significant threat, particularly due to the international movement of infected plants and fruits.

HLB prophylaxis

Since there is no cure for HLB, prevention is essential to limit its introduction and spread. Here are some prophylactic measures recommended by Agrumiverse , your supplier of certified citrus plants :

• Strict import control: Ensure that you avoid the import of infected plants or vectors of infection by complying with phytosanitary regulations.
• Use certified plants: Use healthy citrus plants from certified nurseries for all new plantings.
• Establish physical barriers: Install netting or barriers around orchards to prevent psyllid access.
• Orchard Monitoring: Inspect your trees regularly to quickly detect disease symptoms and signs of psyllid presence.

Means of Combating HLB

In the absence of curative treatment, the fight against HLB relies on the management of vector insect populations and the elimination of infected trees:

Removal of infected trees:

• Removing infected trees is often the only solution to prevent the spread of HLB in the orchard.

Fight against insect vectors:

• Chemical control: Use of specific insecticides to reduce psyllid populations, mainly Diaphorina citri and Trioza erytreae .
• Biological control: Introduction of natural predators of psyllids, such as parasitoid wasps.

Threat Significance

The Asian citrus psyllid and HLB pose a major threat to citrus production worldwide. The impact of the disease is devastating:

• Rapid transmission: The psyllid Diaphorina citri is an efficient vector of the HLB bacterium, rapidly infecting new trees.
• Tree Weakening: HLB causes progressive tree decline, leading to severe reduction in fruit production and often death of infected trees.
• No Rootstock/Cultivar Tolerance: Currently, there are no cultivars or rootstocks resistant to the disease, making prevention all the more crucial.

FAQ

What are the main symptoms of HLB?

Symptoms include asymmetrical yellowing of leaves, mottling along veins, deformed and hard fruit, and progressive decline of the tree.

Which citrus species are most susceptible to HLB?

Sweet oranges , mandarins and their hybrids (tangelos) are particularly susceptible, although most citrus fruits can be affected.

How is HLB transmitted?

HLB is primarily transmitted by the Asian citrus psyllid ( Diaphorina citri ), an insect that feeds on citrus sap and transmits the bacteria as it moves from tree to tree.

Is there a treatment for HLB?

Unfortunately, there is no cure for HLB. Prevention and removal of infected trees are the main control strategies.

How to prevent the appearance of HLB in an orchard?

Prevention is based on the use of certified healthy plants , the control of vector insects and regular monitoring of orchards to detect the first signs of infection.

How can Agrumiverse help prevent HLB?

Agrumiverse , as a supplier to professional citrus growers , offers certified healthy citrus plants and offers personalized technical advice to help prevent the introduction and spread of HLB in your orchards.