Plant Protection Measures in Citrus
Insect Pests of Citrus
- 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%
- 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%)
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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%)
- Fruit cracking
Two types of fruit cracking –
- Radial (Longitudinal – more common)
- 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.
- Apply light irrigation at frequent intervals.
- Regular picking of fruits.
- Apply potassium to the crop.
- 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.
- 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.
- 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
- 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
- Spray with copper fungicide during fruit setting (August) and repeat it at 3 week interval.