Fruit Science

Plant Protection Measures in Citrus

Insect Pests of Citrus

  1. Lemon butterfly (Papilio demoleus):-
  • The tender leaves are damaged by eating from the margin towards the midrib.
  • It appears in April & August – September.


  • Pick up larvae by hand.
  • Spray Malathion at 0.05% or Methyl Parathion at 0.25%


  1. Citrus leaf miner (Phylloenistis citrella)
  • It mines into the surface of young citrus leaves to form a gallery of serpentine tunnels and make them curl.


  • Spray parathion (0.025%) Dimecron (0.1%) or Rogor (0.1%)
  • Spray systemic insecticide like Metasystox (0.03%)


  1. Citrus Psylla (Diaphornia citri)
  • Citrus Psylla is a kind of lice that sucks sap from young leaves, tender shoots, and flower buds.
  • It excretes honeydew which develops the sooty mould fungus.


  • Soil application of systemic insecticides such as Dimethoate 10gm/tree followed by light irrigation.
  • Spray of Dimecron (0.025%) or Parathion (0.025%)
  • Biological control through Tetriasticus radiatus is a hymenopterous parasite.
  1. Stem and bark borers (Indarbela teraonis)
  • The caterpillar bores into the stem and bark. The entry holes are found covered with large quantities of silken webs, consisting of tiny pieces of wood.


  • Hook out grabs and caterpillars from the galleries.
  • Fumigate tunnels by fumigants like Petrol, Formaldehyde, Kerosene oil etc.
  • Adopt phytosanitary measures by way of removing severely affected branches.

Citrus Diseases

  1. Gummosis (Phytophthora, Diplodia natalensis)
  • Affected plant parts, particularly trunk, branches exude gum through cracks on bark which turn brown to black on drying.


  • Remove carefully affected portions with a sharp knife along with some portion of healthy bark. Thereafter washing out the portion properly with a disinfectant like mercuric chloride (1:1000) solution followed by application of Bordeaux paste on the complete cut portion.
  • Make provision for good drainage and avoid excess irrigation.
  • Use resistant Rootstock.


  1. Pink disease (Pellicularia salmonicolour)
  • Branches cause wilting and premature drying during post-monsoon.
  • Affected branches are covered with pinkish coloured fungus.
  • Longitudinal cracking and gumming of the branches.
  • High rainfall is favourable for the proliferation of this disease.


  • Remove affected plant parts and burn them.
  • Apply Bordeaux paste on the cut ends.
  • Spray Bordeaux mixture (5:5:100) twice.
  1. Citrus canker (Xanthomonas citri) (bacterial)
  • Leaves attacked by citrus leaf miner gives easy entry to canker pathogen.
  • Canker is seen in the form of tiny, circular, brown crator-like eruptions on leaves, stems, and fruits.


  • Prune affected twigs before and after the monsoon and burn them.
  • Spray streptomycin sulphate at 500 to 1000 ppm at 20-25 days intervals.
  • Control the leaf miner by spraying metasystox at 0.1 % at regular intervals.


  1. Tristeza virus disease (Corium vialoris)
  • The affected tree lacks new growth during the normal flush period.
  • The tree looks chlorotic sick leaves drop 0ff and twigs die back.
  • Affected trees usually blossom heavily. Tristeza virus is both vector and bud transmissible but not through seed.
  • Vector is a tropical citrus aphid (Aphids citricidus)


  • Raise citrus on tristeza tolerant rootstock: Jatti Khatti, Sweet lime, Karna Khatta, Satgudi, Rangpur lime etc.
  • Use of virus-free buds for budding.
  1. Citrus greening
  • First discovered by Fraser and Singh in India. The causal pathogen is reported to be the Rickettsia–like – organisms (RLO).
  • The leaves of spring growth flush, after reaching maturity develop striking chlorotic patterns, resembling those of zinc deficiency. On leaves, green dots or islands appear against the yellow background.
  • Off-season blooming and later die-back symptoms are seen.
  • Affected fruits develop orange colour first at the bottom end, of gum pockets have been reposted.
  • Transmitted by grafting, and through insects like Citrus psylla.


  • Apply tetracycline hydrochloride through injection (6-10g / tree)
  • Prune affected portion.
  • Spray with Rogor (0.03%)


Physiological disorder

  1. Fruit cracking

Two types of fruit cracking –

  1. Radial (Longitudinal – more common)
  2. Transverse
  • Secondary infection is also common by Aspergillus, Alternaria, Penicillium, etc.
  • Fruit cracking may be due to sudden changes in climate conditions and water stress conditions.

Control measures

  • Apply light irrigation at frequent intervals.
  • Regular picking of fruits.
  • Apply potassium to the crop.
  1. Citrus decline (Dieback)
  • The affected tree becomes blunted, with sparse mottling of leaves, and a sickly appearance. Leaves turn yellow and are shed.
  • There is excessive flowering and poor fruiting.


  • The presence of hardpan due to calcium carbonate
  • Soil salinity
  • Excessive irrigation
  • Non – availability of micronutrients viz N, P, K, and Mg and micronutrients viz. boron, zinc, copper, iron, etc.
  • Incompatibility of rootstock between stock and scion.
  • Mismanagement of citrus.
  • Incidence of insect pests and diseases (Tristeza, greening)


  • Provide proper drainage
  • Avoid excess irrigation
  • Apply recommended doses of manures and fertilizers
  • Follow clean cultivation
  • Always use resistant rootstocks and disease-free bud wood
  • Apply timely plant protection measures for control of disease insect pests.


  1. Granulation
  • Juice sacs become hard, enlarged, and turn opaque greyish in colour.
  • The density of pulp is increased, and juice sacs contain excess calcium, magnesium, sodium, and potassium.
  • Decrease soluble carbohydrates and organic acids.


  • High humidity
  • High as well as low temperature
  • Age of the tree (Young trees are more prone to granulation than older ones)
  • Application of more nitrogen and excess irrigation
  • Size of fruit (Large fruit have more incidence of granulation)
  • Rootstock also affects it.


  • Avoid excess moisture by controlling irrigation.
  • Spray lime at 18 to 20 kg in 450 litres of water.
  • Spray of 2,4-D at 12ppm
  • Spray zinc and copper combined on citrus crops.
  1. Fruit drop
  • Pre-harvest fruit drops common problem
  • Mosambi and Red blood are more prone to fruit drop
  • Valencia late is less prone to fruit drop
  • Reason for fruit drop

Physiological fruit drop: – due to

  • Formation of abscission layer to stem point
  • Imbalance of growth regulators such as auxins, cytokinin gibberellins, etc.
  • Excess or deficiency of certain essential nutrients.
  • Unfavourable weather condition
  • Cultural practices

Control measures

  • Spray 2, 4-D (20ppm) in the month of August
  • Apply recommended doses of nutrients
  • Follow improved cultural practices at the right time in the right way

Pathological fruit drop

  • Alternaria citri and Colletrotrichum gleosporiodes
  • Following a fungus attack on the styler end of the fruit causes styler end rot

Control Measures

  • Spray with copper fungicide during fruit setting (August) and repeat it at 3 week interval.

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