• Definition

  Brown rot is a fungal disease that mainly affects citrus fruits (oranges, lemons, mandarins, etc.). It is caused by fungi of the genus Phytophthora, which are present in the soil and infect fruit, especially when they come into contact with standing water or splashes from infected soil.

  Development Lifecycle

  1. Overwintering : the pathogen survives in soil, plant residues, fruits and diseased branches in the form of mycelium or spores (chlamydospores, oospores).
  2. Favourable conditions : In spring or fall, when the temperature is between 25 and 31°C and the humidity exceeds 85%, the spores germinate.
  3. Dispersal : Splashing rain, irrigation, or standing water allow spores to reach low fruit on the tree.
  4. Infection : Spores penetrate fruit tissues (often through wounds) and cause rot.
  5. Spread : Infected fruit contaminates other parts of the plant or the surrounding soil.

  Symptoms

  • Brown to black spots on fruit, often moist and soft.
  • Unpleasant smell of fermentation.
  • Presence of white mycelium under humid conditions.
  • Crown rot in young plants.
  • Branch dieback or premature fruit drop.
  • During severe attacks: mortality of the young tree.

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  Contributing factors

  • • Temperature between 25 and 31 °C.
    • Relative > humidity 85%.
    • Frequent rainfall or poorly managed irrigation (splashing).
    • Presence of fruit close to the ground.
    • Poorly drained, compact, or waterlogged soils.
    • Inadequate pruning and pruning, leaving open wounds.

Preventive control

• Avoid splashing rain or irrigation on the fruit.
• Prune low branches to avoid contact with the ground.
• Improve soil drainage.
• Space plants properly to ensure proper aeration.
• Disinfect pruning tools.
• Avoid injury to fruit during harvest.

Chemical control

• Application of copper-based fungicides (Bordeaux mixture) as a preventive measure.
• Treatments with systemic fungicides (fosetyl-Al, potassium phosphites) if infection is present.
• Soaking harvested fruit in a fungicide solution before packaging.

Biological control

• Use of antagonistic fungi such as Trichoderma spp. in soil.
• Improvement of soil microbial biodiversity to limit the development of Phytophthora.

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