Citrus Greening

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Citrus Greening (also called Huanglongbing, HLB) is a most devasting disease in which infected leaves are small, upright and show a variety of chlorotic patterns. It has affected million acres of Citrus orchards in the world. It is also known as Huanglongbing (HLB) or yellow dragon disease. Once a tree is infected, there is no cure. It is caused by a vector-transmitted pathogen- Citrus Psyllids

Susceptibility – All citrus crop

Causal organism– Fastidious bacterium Candidatus Liberibacter asiaticum

Fig – Greening symptoms on different citrus cultivar a) Mandarine b) Sweet orange c) Rangpur lime d) Acid lime e) healthy citrus leaf
Source – Bhose et. al., 2015		Fig – Symptoms on fruits
Source – USDA

Symptoms-

  • The early symptoms usually appear on one sector or branch of the tree.
  • Leaves are characterized with blotchy appearance (irregular patches), stunted, leathery and dull green colour.
  • The chlorotic patterns on leaves resembles the spots of zinc deficiencies and iron deficiencies.
  • Severely infected plant shows heavy defoliation and fruit drop with stunted growth and extensive chlorosis.
  • Fruits of affected plant develop yellow patches on the rind surface.
  • Fruits are small, deteriorated, and low in juice content.
  • Many fruits fall prematurely, while those that remain on tree do not colour properly, remaining green on the stylar end/lower end of the fruit (Hence, the name ‘greening’).

Mode of spread:

  • Infected budwoods propagation.
  • Through Insect Vector, Citrus psylla (Diaphorina citri).

Reason of severity-

  • The disease is more severe due to the prevalence of warm temperature of 300 C – 350C and RH- 80- 85%.  

Management-

Cultural PracticesChemical Control
Use of disease-free   planting material.Pruning of symptomatic parts.Proper sanitation of orchard should be maintained.Heavily infected trees should be uprooted and destroyed.Control of vector should be done.Curry leaf tree act as an alternative host for citrus psylla. It should not be grown in the vicinity of the orchard.Precaution Spraying with- Carbendazim 50% WP @ 2g per liter + Streptocyclin @ 0.5g per liter water will reduce the infection of disease.Isocycloseram 9.2% w/w DC + Isocycloseram 10% w/v DC) 0.9 ml per liter.Spinetoram 0.3 ml per liter

Source –  

Book – Handbook of Horticulture