Diplodia citrus dieback

Citrus dieback, caused by the fungus Diplodia citricola, is a significant pathology affecting citrus orchards globally. The fungus functions as a wound parasite, invading the host through natural openings or mechanical damages such as pruning cuts, pest punctures, or weather-related fissures in the bark.

Various citrus species, including lemons, oranges, and mandarins, are susceptible to this pathogen. When trees are stressed by drought, poor nutrition, or secondary pest infestations, they become much more vulnerable to the colonisation of Diplodia citricola, which can thrive in both wood tissues and fruits.

The characteristic symptoms include the appearance of brown or black lesions on branches, which eventually turn into necrotic cankers. As the fungus progresses, the bark may peel away from the wood. This infection often leads to terminal dieback, where the twigs wither and die from the tips downward, eventually impacting the main scaffold branches.

Environmental conditions play a crucial role in disease dissemination. High humidity and temperatures facilitate the production of pycnidia, which are tiny, black, flask-shaped structures that release spores. These spores are disseminated via wind and rain splashes, making disease management challenging during wet, warm seasons in citrus-growing regions.

The economic impact of this disease is substantial, as it leads to reduced yields and tree decline. To effectively manage and mitigate the risks, growers should adopt the following integrated strategies:

• Sanitary pruning of all infected twigs and branches, ensuring clean cuts.
• Immediate treatment of pruning wounds with protective fungicides or mastic sealants.
• Application of copper-based fungicides to reduce the inoculum load on the bark surface.
• Improving tree vigor through adequate irrigation and balanced nutrient management to prevent predisposition to infection.