Integrated Management of Citrus Excoriosis (*Diaporthe citri*) in Argentina

Etiology and Pathogenesis of Diaporthe citri

Citrus production faces various phytosanitary challenges that directly impact crop quality and yield. Among these, citrus excoriosis, primarily caused by the fungus Diaporthe citri (formerly Phomopsis citri), represents a significant concern for producers in the region. This disease affects branches, leaves, and, most critically, the fruits, diminishing their commercial value and the overall productivity of orchards. Understanding its life cycle and developing integrated management strategies are fundamental to mitigating its effects in orchards across Argentina and Latin America.

Citrus excoriosis manifests through characteristic lesions on various parts of the plant. On fruits, initial symptoms include small brown or blackish spots that expand, forming rough, raised scabs. These lesions can merge, covering large areas of the fruit surface and affecting their appearance, rendering them unviable for the fresh market. On young branches and twigs, necrotic lesions are observed that advance, potentially causing girdling and dieback of shoots. Leaves, although less affected, may show small chlorotic spots that evolve into necrotic lesions. The pathogen’s dispersal occurs mainly through rain splash and dew, with spores germinating under conditions of high humidity and warm temperatures. The periods following flowering and initial fruit development are the most critical for infection. The presence of infected plant material in the tree canopy or on the soil acts as the primary inoculum for new infections.

Impact of Fungal Lesions on Citrus Fruit Quality

The implementation of adequate cultural practices constitutes the first line of defense against excoriosis. Rigorous sanitary pruning is essential, removing dead, diseased, or symptomatic branches, which significantly reduces the inoculum source. It is crucial to perform this pruning during dry periods to prevent spore dissemination and to disinfect cutting tools between trees. Managing canopy density through thinning prunes improves air circulation and sunlight penetration, decreasing relative humidity within the canopy and creating a less favorable environment for spore germination. Efficient irrigation, preferably drip or micro-sprinkler systems, avoids prolonged wetting of leaves and fruits, unlike overhead sprinkler irrigation which favors the spread and establishment of the fungus. Furthermore, balanced nutrition strengthens the plant, making it more resistant to stress and infections. Selecting less susceptible citrus varieties, where possible, also contributes to long-term prevention. Management of pruning waste and fallen fruits is vital to reduce the inoculum load in the orchard soil.

For excoriosis management, strategies combining chemical and biological control are employed within an Integrated Pest Management (IPM) framework. Copper-based fungicides, such as copper oxychloride or copper hydroxide, are widely used for their protective and residual action. Other options include systemic or contact fungicides, applied at key phenological stages of the plant, especially during early fruit development when susceptibility is highest. It is essential to follow recommended dosages and application frequencies to prevent pathogen resistance and minimize environmental impact. The current trend focuses on reducing agrochemical use and seeking more sustainable alternatives. Biological control offers a promising avenue through the application of antagonistic microorganisms, such as certain strains of Trichoderma spp. or Bacillus subtilis, which compete with the pathogen or produce antifungal compounds. Recent research explores the potential of plant extracts and essential oils with fungicidal properties as biopesticides, integrating them into management programs that aim for ecological balance and cleaner production, relevant for the demands of markets like Mercosur.

Pathogen Dispersal and Critical Environmental Factors

Modern agriculture incorporates technological tools to optimize disease management. Remote sensors and drones equipped with multispectral cameras allow for aerial monitoring of large crop areas, identifying zones with plant stress or potential excoriosis outbreaks before symptoms are visible to the naked eye. This early detection facilitates the localized application of treatments, reducing input use and operational costs. Geographic Information Systems (GIS) and precision agriculture platforms integrate this data to generate risk maps and guide management decisions. Furthermore, predictive models based on climatic conditions (temperature, humidity, precipitation) are being developed to alert about high-risk infection periods, enabling more timely preventive treatments. Genetic research is also advancing in identifying resistance markers in citrus varieties, opening the door to developing new cultivars more resilient to excoriosis and other diseases. The implementation of these technologies, along with consultation with organizations like INTA in Argentina, enhances the efficiency and sustainability of regional citrus farming in the face of phytosanitary challenges and climate change.

Effective management of citrus excoriosis demands a holistic and adaptive approach. The strategic combination of preventive cultural practices, rational fungicide use, exploration of biological solutions, and the incorporation of monitoring and precision technologies are pillars for sustainable and profitable citrus production. Investment in research and continuous producer training are key to confronting emerging challenges and ensuring the viability of this important agricultural sector in Latin America.