Citrus: Diseases, Symptoms and their Management

Diseases of Citrus Fruits

1. Foot Rot or Gummosis Diseases of Citrus

Causal Organism:  Fungus; Phytophthora parasitica, P. palmivora, P. citrophthora

Symptoms:

  • Symptoms of the condition manifest as yellowing of leaves, followed by bark cracking and the formation of abundant gum on the surface.
  • The primary mode of infection is through the use of infected planting material.
  • The extensive gumming eventually leads to complete decay of the bark, causing the tree to dry out due to a girdling effect.
  • In some cases, the plant may experience heavy blossoming prior to death, with the fruits failing to mature before the plant perishes.

Management:

  • Applying Bordeaux mixture to the stem, specifically, 1 meter above the ground level, has been found to be effective in controlling the disease.
  • Additionally, spraying and drenching with Ridomil MZ 72 at a concentration of 2.75 g/l or Aliette at 2.5 g/l has shown to be effective in managing the disease.

2. Ganoderma Root-Rot Diseases of Citrus

Causal Organism: Fungus; Ganoderma lucidum

Symptoms:

  • The disease first appears in the soil, damaging one or more lateral roots.
  • The fungus spreads along the surface of the bark, gradually darkening in colour.
  • The fungus advances towards the base of the main trunk over time.
  • As the condition progresses, the damaged tissues become noticeably light, bloated, and spongy due to water accumulation.
  • During the wet season, bracket-like fungal fructifications may grow near the base of the trunk, suggesting the presence of the disease.

Management:

  • In the plant basin, Aureofungin solution (1.5 g in 5 litres of water) and Vitavax (500 ppm) are effective.

3. Dry Root Rot

Causal Organism: Fungus; Macrophomina phaseolina

Symptoms:

  • It is distinguished by fluid degradation of the bark in the early stages and a dry shredded bark condition with hard, dead wood underlying in the later stages.
  • The afflicted roots have a foul aroma.
  • The affected tree defoliates and produces a large number of small-sized fruits.

Management:

  • Applying Bordeaux mixture to the stem.

4. Scab or Verucosis

Causal Organism: Fungus; Elsinoe fawcettii

Symptoms:

  • The lesions begin as little semi-translucent spots on the underside of the leaves and progress to sharply defined pustular elevations.
  • Later phases of development frequently result in twisted, wrinkled, stunted, and malformed leaves.
  • Lesions on the fruit are corky protrusions that frequently rupture into scabs.
  • A circular depression with a pink-to-red centre can be seen on the opposite surface of the warty growth.

Management:

  • Spraying of Bordeaux mixture or Blitox (0.3%) is quite effective.

5. Citrus Canker

Causal Organism: Bacteria; Xanthomonas citri

Symptoms:

  • During the wet season, it is the most dangerous bacterial disease of sour lime.
  • Symptoms of the disease emerge on the leaves, branches, and fruit stalks.
  • Canker lesions begin as yellowish patches that develop to form elevated, rough brownish pustules.
  • These pustules have a distinct golden halo around them. Canker lesions on the fruits are limited to the rind and do not enter the fruit’s flesh.

Management:

  • During February, October, and December, three sprays of Streptocycline 100 ppm (10 g Streptocycline + 5 g Copper Sulphate in 100 litres water) or Blitox (0.3%) or neem cake suspension (1 kg in 20 litres water) might control the disease.

6. Tristeza Virus Quick Decline Disease

Causal Organism: Virus

Vector: Aphid (Toxoptera citricida)

Symptoms:

  • The symptoms begin with the dieback of small branches and twigs, yellowing of leaves and heavy bearing of small fruits.
  • As the disease advances the symptoms, intensify resulting in severe chlorosis and mottling.
  • The feeder roots of the affected plants die, the bark of the larger roots is distorted and brittle, and dry rot symptoms are observed in the case of lateral roots.
  • After 7-8 years the branches of the affected plant dry up completely and the plants wilt completely.
  • Few trees show wilting symptoms overnight and completely dry up in 2 or 3 days.

Management:

  • The best way to combat this disease is to limit the aphid population by the use of pesticides in nurseries and plantations.

7. Greening Diseases of Citrus

Causal Organism: MLOs

Vector: Grafting and Citrus psylla (Diaphorina citri)

Symptoms:

  • The affected trees are stunted, with noticeable leaf and fruit drops. Some branches on the damaged tree have significant twig dieback signs, while others appear to be normal.
  • The fruits of affected trees stay predominantly green even after maturity, and those that are directly exposed to sunlight have a noticeable yellow area on the rind surface.
  • Disease fruits are worthless due to their small size, distortion, low juice content, and bland flavour.

Management:

  • Controlling the vector population can help to keep this disease at bay in the field. Nymphs and adults are controlled by spraying Phosphamidon (0.025%) or Parathion (0.025%).
  • Dimethoate 10% granules applied to the soil around the plant basin effectively control citrus psyllids.

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