🍊 Diseases of Citrus

Citrus orchards suffer from several diseases that damage roots, bark, leaves, twigs, and fruits at the same time. This makes disease diagnosis in citrus especially important, because management depends on knowing whether the problem is soil-borne, bacterial, or viral.

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Major Citrus Diseases Covered in This Lesson

The original lesson brings together four major citrus disease groups:

• gummosis / foot rot / collar rot
• scab
• canker
• tristeza (quick decline)

Each disease affects different plant parts and spreads in a different way, so the management approach also changes.

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Gummosis, Foot Rot, and Collar Rot

Causal organisms: Phytophthora parasitica, P. palmivora, P. citrophthora

This disease usually begins with yellowing of leaves, cracking of bark, and profuse gumming on the trunk region. When infection becomes severe, bark rots, girdling occurs, and the tree may dry up. In advanced cases near the collar region, the disease appears as foot rot or collar rot.

Favorable conditions

• poor drainage
• prolonged contact of trunk with water
• flood irrigation
• heavy soils and waterlogging

Management logic

• plant in well-drained sites
• avoid direct contact of irrigation water with the trunk
• use ring irrigation
• use tolerant or resistant rootstocks where available
• scrape diseased bark and disinfect the area
• drench or spray with suitable anti-oomycete fungicides such as Ridomil MZ or Aliette as noted in the source

In citrus, water management is a disease-management tool. Poor drainage is one of the strongest predisposing factors for gummosis.

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Citrus Scab

Causal organism: Elsinoe fawcetti

Scab affects leaves and fruits. Early lesions appear as small semi-translucent dots that later become raised, corky, and scab-like. Distortion of leaves and corky projections on fruits are characteristic signs.

Management logic

• collect and destroy infected leaves, twigs, and fruits
• reduce carry-over inoculum
• use fungicidal protection such as carbendazim-based spray as described in the notes

The practical point here is that citrus scab mainly reduces market quality and young tissue health.

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Citrus Canker

Causal organism: Xanthomonas campestris pv. citri

Canker is a bacterial disease that is important because it spreads through splashing rain, wind-driven injury, and wounds created by leaf miner damage.

Characteristic features include:

• circular lesions with yellow halo
• lesions on leaves, twigs, and fruits
• twig girdling in severe infection
• reduction in fruit market value

Favorable conditions

• free moisture
• warm temperature around 20-30 degrees C
• injury on young flush, especially due to leaf miner

Management logic

• prune badly infected twigs before monsoon
• control leaf miner during flush
• use copper-based sprays or antibiotic-supported measures noted in the source
• reduce spread during wet weather

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Tristeza or Quick Decline

Causal organism: Citrus tristeza virus (CTV)

Tristeza is a viral disease associated with decline, poor vigor, and collapse in susceptible scion-rootstock combinations. Unlike gummosis or canker, it cannot be managed through fungicide or bactericide logic.

The key management principle is:

• use healthy propagation material
• select tolerant rootstocks
• manage vector transmission where relevant

This disease is a good example of why citrus pathology must be diagnosed accurately before control advice is given.

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Summary Cheat Sheet

Disease	Cause	Main symptom clue	Core management idea
Gummosis / foot rot	Phytophthora spp.	Bark cracking, gumming, collar rot	Drainage + trunk protection + anti-oomycete treatment
Scab	Elsinoe fawcetti	Corky raised lesions on leaves and fruit	Sanitation + fungicidal protection
Canker	Xanthomonas pv. citri	Haloed lesions on leaves, twigs, fruits	Pruning + copper-based protection + leaf miner control
Tristeza	CTV	Quick decline and graft-related susceptibility	Healthy planting stock + tolerant rootstocks