Protecting citrus from disease and decay.

Citrus fruit is one of the most important product groups in the fresh produce sector. Consumers expect high-quality oranges, mandarins, lemons and grapefruits all year round. Yet beneath the attractive peel, citrus hides a vulnerability: it is highly susceptible to a wide range of diseases caused by fungi, bacteria, and viruses. These not only affect production in the orchards but also influence product quality, shelf life, and even international trade.

Fungi are the leading cause of visible decay in citrus fruit, often resulting in soft rot, mold growth, and off-odors. Some infections originate in the orchard but only become visible later in the supply chain, while others occur during harvest and handling.

• Blue Mould (Penicillium italicum) & Green Mould (Penicillium digitatum)
  These aggressive fungi develop on small wounds in the peel. They create circular white mycelium followed by green or blue spores. Once a single fruit is infected, spores can easily spread to surrounding fruit, often referred to as nest rot.

• Black Rot (Alternaria)
  Typically visible at the navel end of oranges, this fungus causes dark, sunken lesions and internal blackening of the fruit.

• Brown Rot (Phytophthora)
  Infection usually occurs in the orchard due to splashing soil particles during rain. It develops later in storage as a brown, rancid-smelling rot.

• Anthracnose (Colletotrichum)
  Often seen on weak or overripe fruit, leading to necrotic spots, particularly near the stem end.

• Citrus Black Spot (CBS, Phyllosticta citricarpa)
  A quarantine disease with major trade implications. It causes dark spots and blemishes on the peel, reducing fruit quality and leading to strict phytosanitary restrictions for exporting countries.

While bacteria rarely cause the fruit to rot completely, their impact on trade can be severe:

• Citrus Canker (Xanthomonas citri)
  Characterized by corky, wart-like lesions on peel and leaves. While the fruit remains edible, the disease weakens trees and reduces yields. Because it spreads easily, countries impose strict import restrictions when it is detected.

Viruses are harder to detect on fruit but can devastate citrus orchards:

• Citrus Tristeza Virus (CTV)
  One of the most serious citrus diseases worldwide. Although it does not affect the fruit directly, it can kill entire trees or drastically reduce yields. To minimize spread, EU regulations stipulate that citrus fruit may not enter with leaves and that stem length must be under 2 mm.

The fight against citrus diseases requires action at every stage of the supply chain:

• In the orchard: preventive treatments, good pruning and soil management

• At packing stations: careful sorting, use of post-harvest fungicides, and protective wax coatings

• During transport: strict temperature control, ventilation, and rapid cooling to slow down fungal growth

• At arrival: expert inspections to identify symptoms early and prevent further spread

Do you want to expand your knowledge of citrus diseases, learn how to identify and prevent them?

HDG Academy can help!