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.

Control

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

2. 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.

Control

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

3. 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.

Control

• 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.

4. 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.

Control

• 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.

Control

• 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.

2. 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.

Control

• Remove affected plant parts and burn them.
• Apply Bordeaux paste on the cut ends.
• Spray Bordeaux mixture (5:5:100) twice.

3. 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.

Control

• 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.

4. 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)

Control

• Raise citrus on tristeza tolerant rootstock: Jatti Khatti, Sweet lime, Karna Khatta, Satgudi, Rangpur lime etc.
• Use of virus-free buds for budding.

5. 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.

Control

• 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.

2. 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.

Causes

• 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)

Control

• 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.

3. 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.

Causes

• 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.

Control

• 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.

4. 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.