Citrus diseases and their control

Major Citrus diseases are given below:-

First symptoms are dark staining of bark which progresses into the wood.
Bark at the base is destroyed resulting in girdling and finally death of the tree.
Bark in such parts dries, shrinks and cracks and shreds in lengthwise vertical strips.
Later profuse exudation of gum from the bark of the trunk.
Infection extends to crown roots.
Prolonged contact of the trunk with water as in flood irrigation; water logged areas and heavy soils.
Soil inhabitants.
Sporangia spread by splashing rain water, irrigation water and the wind.
Irrigation water and wind.

Injuries to crown roots or base of the stem during cultural operations should be avoided.
If the lesion has girdled less than ½ the girth, remove the diseased bark with a knife along with ½” of uninvaded bark.
The bark of trunk should be coated with Bordeaux paste.

Attacks leaves, twigs and fruits of mandarin.
Sour orange, lemon, mandarin, tangelos extremely susceptible Grapefruit, sweet oranges and acid lime highly resistant. Severe in rainy seasons.
On the leaves, the disease starts as small pale orange coloured spots.
The leaf tissue is distorted to firm hollow conical growths with the lesion at the apex.
The crest of these growth becomes covered with scabby corky tissue colour at first but later becomes dark olive with age.
Lesions most common on the undersurface of the leaf. They penetrate leaf and are later visible on both sides.
Infected areas run together and cover a large area.Leaves wrinkled, distorted and stunted.
On twigs, similar lesions are produced.
They form corky outgrowths.On fruits irregular scably spots or caked masses produced.
Cream colour in young fruits; dark olive grey in old fruits.
Fruits attacked when young become misshapen with prominent warty projections. They drop prematurely.

Acid lime, lemon and grapefruit are affected. Rare on sweet oranges and mandarins.
Affects leaf, twig and fruits. In canker, leaves are not distorted.
Lesions are typically circular with yellow halo; appear on both sides of leaf, severe in acid lime (difference from scab) When lesions are produced on twigs, they are girdled and die.
On fruits, canker lesions reduce market value.

Streptomycin sulphate 500-1000 ppm; or Phytomycin 2500 ppm or Copper oxychloride 0.2% at fortnight intervals.
Control leaf miner when young flush is produced.
Prune badly infected twigs before the onset of monsoon

citrus tristeza

Lime is susceptible both as seedling or buddling on any root stock.
But mandarin and sweet orange seedlings or on rough lemon, trifoliate orange, citrange; Rangpur lime root stocks tolerant; susceptible root stocks are grape fruit and sour orange.
In sweet orange or mandarin on susceptible root stocks, leaves develop deficiency symptoms and absise.
Roots decay, twigs die back. Fruit set diminishes; only skeleton remains.
Fine pitting of inner face of bark of sour orange stock.
Grapefruit and acid lime are susceptible irrespective of root stock.
Acid lime leaves show large number of vein flecks (elongated translucent area).
Tree stunted and dies yield very much reduced. Fruits are small in size.
Use of infected bud wood and Toxoptera citricida (aphid) is the important vector.

greening of citrus

This disease affects almost all citrus varieties irrespective of root stock.
Stunting of leaf, sparse foliation, twig die back, poor crop of predominantly greened, worthless fruits.
Sometimes only a portion of tree is affected.A diversity of foliar chlorosis.
A type of mottling resembling zinc deficiency often predominates.
Young leaves appear normal but soon assume on outright position, become leathery and develop prominant veins and dull olive green colour. Green circular dots on leaves.
Many twigs become upright and produce smaller leaves.
Fruits small, lopsided with curved columella. The side exposed to direct sunlight develops full orange colour but the other side remain dull olive green.
Low in juice and soluble solids, high in acid. Worthless either as fresh fruit or for processing. Seeds poorly developed, dark coloured, aborted.
Infected budwood; psyllid vector-Diaphorina citri

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