Citrus Canker

Citrus Canker
Citrus Canker
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C. O. Xanthomonas campestris

Symptoms:

• Canker appears on leaves, twigs, petioles, branches, fruits and thorns.
• The lesions appear as minute water soaked round, yellow spots. These pustules are surrounded by a characteristic yellow halo.
• The market value of the fruits is considerably reduced by the canker spots, though such infections are mostly confined to the fruit skin.
• Severe infections of the twig and stem may cause die-back symptoms.
• Favourable conditions: Free moisture for 20 minutes at 20-30°C temperature for disease development
• Citrus leaf miners (Phyllocnistis citrella) and rain splashes helps in the dissemination of the pathogen.

Management:

• Prune out and burn all canker infected twigs before monsoon.
• Periodical spraying of bactericides along with an insecticide.
• Select seedlings free from canker for planting in main field.
• Three sprayings of Streptocycline (1g) + Copper oxy chloride (30g) in 10 litres of water at an interval of 20 days during rainy season is effective for leaf canker.
• Fruit infection can be prevented by two sprays of Streptocycline (1g) + Copper oxy chloride (30g) in 10 litres of water at marble stage followed by another spray 30 days later.


Gummosis
Gummosis:
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C. O.: Phytophthora citrophthora

Symptoms:

• Water soaked large patches on the basal portions of the stem and branches near the ground level.
• Bark split open and through which a gum like ooze exudates.
• Prior to death, the plant usually blossoms heavily and dies before the fruits mature.

Favourable condition:

• Incidence is more in black soils than in light soil.
• High water table leads to high incidence.
• The disease is severe in high rainfall areas.
• Presence of water facilitates easy infection.
• Humid weather with optimum temp. 250-300C is more favorable for infection.

Management:

• Selection of proper site with adequate drainage and high budding (30 to 46 cm or above).
• Provision of an inner ring about 45 cm around the tree trunk to prevent moist soil. (Double ring method of irrigation)
• Avoid irrigation water from coming in direct contact with the trunk.
• Avoid injuries to crown roots or base of stem during cultural operations.
• Avoid excessive irrigation
• Provide adequate drainage facilities in the orchard.
• Scrape the diseased portion with a sharp knife. Protect the cut surface with Bordeaux paste at a height of 70 cm above the ground level followed by spraying of 0.3% fosetyl- AL reduces the spread.
• Soil drenching with 0.2% metalaxyl and 0.5% Trichoderma viride commercial formulation is also effective.


Tristeza or quick decline
Tristeza or quick decline:
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C. O.:Citrus Tristeza Virus (CTV)

Symptoms:

• Tristeza affected trees look chlorotic and sickly in the early stages.
• Gradually the leaves drop and the defoliated twigs show die-back.
• The declining trees die gradually but sometimes apparently healthy trees die suddenly.
• In sweet orange, the specific symptom of tristeza is honeycombing, a fine pitting of inner face of bark in the portion of trunk below the bud union vermiform or linear pits appear in the woody cylinder.
• Diseased trees usually blossom heavily. Trees with stem pitting are stunted and set less fruits. The fruits are of smaller size and of poor
• As the fruits develop, the tree wilts partly or completely.
• The disease primarily spreads through grafting and budding.
• In field secondary transmitted by citrus aphid (Toxoptera citricidus) and parasitic dodder (Cuscuta reflexa) .

Management:

• Strict quarantine measures to be enforced.
• Use certified budwood free of CTV.
• Remove all diseased trees as and when the disease is noticed. For sweet orange and mandarin avoid susceptible root stocks.
• For acid lime, use seedling preimmunised with mild strain of tristeza virus (Cross protection).
• Periodic sprays of systemic insecticides reduce the secondary spread of the disease in the orchard.