Citrus decline is a serious problem causing concern not only to growers
but also to researchers and policy makers.
In the condition of decline, the affected trees do not die immediately
but remain in a state of decadence and unproductiveness after having
performed well initially.
Prominent among the various factors responsible for citrus decline
are diseases caused by viruses, bacteria and fungi.
Symptoms caused by infectious agents resemble those of improper nutrition,
incompatability, cultural abuses and physiological disorders.
It is the primary duty of the diagnostician to differentiate between
the several agencies that cause similar symptoms, only then can proper
control measures be applied and the disease cured.
In this chapter, an attempt is made to 1) indicate the various diseases
commonly occuring in Andhra Pradesh that may lead to decline; (2) describe
symptoms of each disease in sufficient detail to enable identification,
(3) indicate the causal organisms and their mode of action; and (4)
recommend remedial measures.
Diseases caused by viruses are dreaded, since there is no cure.
The only way to avoid such diseases is to use virus-free (nucellar)
certified saplings or budlings for planting.
With this objective in view, a nucellar Sathgudi sweet orange bud
bank has been developed at the Citrus improvement Project, Tirupati
from which 4-5 lakh virus-free certified buds are supplied every year
to registered nurserymen and government agencies.
Hence, Citrus growers are advised to use only material from well known
In India, citrus canker is endemic and occurs in all
the citrus growing areas. It is reported from Punjab, Tamil Nadu, Andhra
Pradesh, Karnataka, Rajasthan, Madhya Pradesh, Assam, Uttar Pradesh.
This is more commonly observed on leaves, twigs and fruits
of acid lime than on sweet orange.
Water soaked roundish yellow spots on leaf
Canker on twig
Canker on stem
Canker on acidlime
Canker on sweet orange fruit
Initially it shows up on leaves as small, raised translucent
Over a time, the epidermis over the spot ruptures to expose
a crater-like spongy, tan-coloured tissue.
A yellow halo surrounds the spot till it becomes old.
Old lesions are corky, irregular in shape and brown in colour.
The under surface shows greater involvement.
Cankered leaves are seldom retained to full maturity.
Lesions develop on petiole and midrib, resulting in early leaf fall.
On the twigs the lesions appear water-soaked and dark green first
and later turn brown.
The pustule is corky, but without a crater-like depression.
In severe cases, the twigs dry up.
Canker has also been observed on acid lime roots as slightly raised
On fruit, the infection appears as water-soaked lesions, similar to
those on leaves except for the yellow halo and creater-like depressions,
which appear only in the later state of infection.
Cankered fruit drop prematurely.
In sweet orange, the inner contents are affected while in acid lime
the ifection is confined to the flabedo.
Oozing of gum from the cankered pustule, is common.
Etiology And Spread
The disease is caused by Xanthomonas citr.
Three strains of the pathogen have been distinguished by host reaction
viz., (i) Cancrosis A, the common farm, which is extremely virulent
on grape fruit, sweet oranges and sour oranges and to a lesser degree
on others, (ii) Cancrosis B, which is virulent on lemons, but not on
grape fruit and sweet oranges; and X.citri which attacks acid
Canker-infected leaves, twigs etc, serve as the source of inoculum
to spread the disease from season to season.
However, the cankered leaves drop off early and bacteria perish rapidly
in the soil.
Infected leaves do not serve as the main source of infection and the
carryover of the disease from season to season is mainly from cankerous
lesions or twigs and branches.
The bacterium enters the host through stomata or wounds.
It multiplies in the intercellular spaces, dissolves the middle lemella
and establishes in the cartex region.
Canker pustules develop and exude bacteria in the form of gummy substance.
They are freely disseminated, chiefly by wind and to a considerable
extent by rains.
Citrus leaf miner (Phyllocnistis Citrella) helps dissemination
and infection of citrus canker.
Leaves affected by miner and canker and get distorted and drop off
The injury to the leaf epiderins made by the burrowings of leaf miner
serve as an easy opening to the canker bacterium and the canker lesions
appear throughout in the zigzag manner.
Prevalence of 20-35° C temperature, high humidity and the presence
of moisture on the host surface for 20 minutes or more favours incidence
A positive correlation exists between the rainfall and canker disease
The pathogen can survive in the unsterlized soil upto 9 days.
It is resistant to drying but direct exposure to sunlight kills the
bacterium within 2 minutes.
1. The only method of tackling the disease would
be to prevent or reduce its incidence by
a) Pruning all the canker-infected twigs before monsoon
and burning them.
b) Periodical spraying of suitable bactericides along with
c) By using canker resistant varieties.
2. In case of sweet orange, three sprayings at monthly interval
should be carried out of, streptocycline 100 ppm (i.e. 100 parts per million,
i.e. 1 g of chemical in 10 litres of water) or 0.2% Mancozeb (2 g of Mancozeb/litre
of water) in combination with 0.3% copper oxychloride (3 g of oxychloride/litre
of water). The first spray should be done when the fruits are marble-sized,
irrespective of the appearance of the symptoms.
3. In case of acid lime, the spraying should be done four
times at monthly interval in the rainy season and after the dead twigs
have been pruned.
4. "Tenali Selection" acid lime was found to be tolerant
This disease is believed to be caused by a virus and appears at any
time after 5 years of planting.
The most obvious symptom is the formation of small groove
with honey-coloured gum encircling the bud joint on the wood
with a corresponding projection on the bark.
Drying of the tree is common in severe cases.
Bud union crease
Root stocks such as sweet orange, Cleopatra mandarin, Karhakatta and
Rangpur lime do not develop the disease and should therefore be used
at the time of propagation to avoid occurrence of this disease at a
Virus free certified buds should be used for propagation.
Dry root rot : Macrophomina phaseolina,
Fusarium spp. and Diplodia natalensis Pole Evans.
Dry root rot is a major problem in all citrus growing areas of Andhra
Pradesh in both sweet orange and acid lime.
Sweet orange trees on Jamberi root stock are more susceptible to this
disease than those on the Rangpur lime stock.
The affected plant wilts in the early stages, resulting in ultimate
death in the advanced stages which may occur in one month.
Dry root rot (dried young tree)
Dry root rot(dried roots)
The disease is characterised by wilting, drooping and yellowing
Moist decay of root bark is seen in the early stages and a
dry, shredded condition of the bark with hard dead wood underneath,
is common in the later stages.
Affected roots emit a bad odour and there is some discolouration.
Excessive flowering, heavy crop of small-sized fruit and ultimate
death of affected trees takes place in the last stages.
Etiology and Spred
The exact cause of the diseases is not clear.
Among the fungi, Macrophomina Phascolina, species of Diplodia
and Fusarium are reported to be mainly responsible.
The disease has been ascribed to excessive moisture or drought irregular
manuring, poor aeration, heavy soils, close planting and root injuries,
inadequate supply of nitrogen besides the fungi.
The incidence of dry root rot is the cumulative effects of defective
soil, age of plantation, attack of species of Diplodia, Fusarium
If only one or two roots are affected and the taproot
and crown are still in good condition, the diseased roots may be cut
The cut surface should be protected with Bordeaux paste.
Deep ploughing or digging which are likely to injure
roots should be avoided.
Leaf mulch in the tree basins during the dry season helps
in conserving the soil moisture and thereby reducing disease incidence.
Foliar sprays with Urea (4.5 kg in 450 litres of water)
may reduce the disease incidence.
Application of 10 kg of neem cake followed by soil drenching
with 0.5% Trichoderma vride formulation + 0.2% copper oxy chloride in
the early stages of infection helps in reducing the disease intensity.
The disease is effectively checked if the tree basin
is drenched with 0.1% Carbendazim, (1 g of Carbendazim per litre of
water) followed by another drenching of 0.25% Mancozeb (2.5 g of Mancozeb
per litre of water) or 0.2% Chlorothalonil (2g of Chlorothalonil per
litre of water), 12-24 hours after irrigation, at monthly intervals.
One litre of each chemical fluid should be used per
sq.m. area of the basin.
Felt disease is observed in Guntur, Godavari and Cuddapah
districts of Andhra Pradesh and Madurai and Tirunelveli districts of
Tamilnadu. It is very severe in acid lime plantations around Tenali
in Guntur district. This disease starts with the onset of monsoon in
case of acid lime.
A soft, felt-like fungal growth encircles the twigs and branches.
The fungus grows over the bark and does not penetrate the surface.
The growth is light brown to grey in colour and colonies of
scale insects can be seen underneath it.
This results in dying of stems.
Felt like leathery fungal growth on twig
Etiology and Spread
The disease usually starts with the onset of monsoon
rains and continues throughout the rainy season. During winter the felty
growth bursts and some of it gets peeled off.
Pruning and destruction of the diseased twigs.
Spraying of monocrotophos 0.05% (1/2 ml of monocrotophos/litre of
water) with Zineb 0.25% (2.5 g of zineb/litre of water) twice at monthly
intervals with the onset of monsoon checks the disease.
Ganoderma root rot is seen in old and neglected orchards
of sweet orange, acid lime and mandarin. Also attacks mango, jackfruit,
gulmohur, acasia, coconut and arcanut. Occurs commonly in sweet orange
and acid lime.
Bracket at the base of the tree
The disease starts in the soil, in one or more of the lateral
Whitish fungal strands spread along the surface of the bark
of the root and gradually move to the bottom of the trunk.
The affected tissue becomes swollen, spongy and waterlogged
and bracket like fungal fruiting bodies appear at the base of
Wilting and death of the limb corresponding to the lateral
root/roots is common.
Removal of dead or decaying old stumps from the orchard.
Treating the basal portions of the stakes used as supports to the
young seedlings with fungicide.
Growing green manure crops and incorporating the same in Citrus orchards.
Periodical collection and destruction of brackets found near the collars
of other hosts.
Treatment of the disease can be useful in early stages when only one
or two roots are involved. The inferted roots should be cut and destroyed.
Soil drenching with 0.5% Trichoderma viside formulation +m0.3% copper
oxychloride solution is promising.
Sweet orange, Jamberi (Rough lemon) and Rangpur lime are susceptible
to this disease.
Rainy season and winter are the most congenial times for its occurance.
Spots on lower leaf surface
Small yellow or translucent spots appear on the lower surface
of the leaves.
These gradually turn black or chestnut brown in colour and
look like greasy spots.
Sometimes, many spots coalesce to form one huge spot.
They are rarely seen on the upper surface of the leaves. Leaves
with many spots drop prematurely.
Etiology and Spread
The occurance of this disease is common under humid conditions.
The pathogen survives on dead leaves, twigs and fruits.
In moist weather the sparres ooze out and are disseminated by winds,
birds, insects and other agents and reach fresh leaves, twigs and fruits.
Fruits are infected only when the surface is wet for atleast 12 hours
Spraying with copper oxychloride 0.3% (3 g of copper oxychloride/litre
of water) or Zineb 0.25% (2.5 g of zineb/litre of water) once at new
flush emergence is effective.
The lower surface of the leaves should be sprayed with the fungicide
All the three commercial cultivars of sweet orange grown in Andhra
Pradesh viz., Sathgudi, Mosambi and Batavian are susceptible to this
The rot is most prevalent on fruit maturing in the rainy season (Angam
crop) and seldom noticed in summer (Gyrangum and Edagaru crops).
It is not known to affect acid (Kagzi) lime.
This disease sets in on fruit nearing maturity as a small
brown spot at the button and spreads from the stem end to stylar
The spot develops into a dark brown patch with a light brown
The entire fruit on the tree may rot and soften.
Some of them rot and fall off while others may dry up on the
tree itself, and remain hanging.
Pre-harvest stem-end rot
Etiology and Spread
More than one pathogen is known to cause the disease viz.,Colletotcichum
gloeosporioides and Gloeosporium species.
Trees damaged by gummosis, insects, drought, malnutrition etc are
more vulnerable to infection by the pathogens. C.glocosporioides
remains in a dormant or Quiescent conditions in the dead turing
Sparers of the fungus germinate on surface of citrus fruits forming
Appresoria produce infection hyphae which remain latent within the
upper layers of peel, even after the fruit matures.
Injuries on fruit peeling and over matured fruits of oranges and grape
fruit function as sites of infection.
This disease is serious on limes, lemons and citrons.
All the affected fruit which have fallen onto the ground and which
have dried up along with the pedicel (stalk) must be collected and destroyed.
Spraying 0.05% Carbendazim (5 grams of Carbendazim in 10 litres of
water) three times at monthly intervals during June, July and August
will control the disease.
It is estimated that one fruit in every four harvested fruits is affected
with post-harvest decays resulting in rotten fruit reaching the consumer.
Attack by micro-organisms is probably the most serious cause of post-harvest
loss in perishables.
Pathogens inflicting perishable cause both qualitative and quantitative
Quantitative pathogenic losses are due to the rapid and extensive
breakdown of host tissue, by micro-organisms.
Qualitative pathogenic losses are thr result of discololuration.
Management of post-harvest diseases of citrus crop consists of careful
handling of fruit during harvesting, transportation, packing and storage
conditions at the market places (mandis).
However, storage life can be prolonged and rot prevented to a great
extent, if fruits are dipped in a mixture of 3% wax emulsion and 0.05%
Carbendazim (0.5 g of Carbendazim/litre of water), before packinag the
fruit in boxes for transporting.
Injured or damaged portion of fruit is susceptible to all types of
rots. Hence, to avoid the occurence of rots, careful handling and packing
of the fruit is essential.
The fungus from one rotten fruit is easily passed on to the rest of
the fruits, thus spoiling the complete lot in the box.
In India, Sooty mould is common in all the citrus growing
regions. However, the diseases is severe in South India, Assam and Kumaon.
The Intensity of sooty mould is related to the infestation of scale
and other insect pests.
Sooty mould on leaf
Sooty mould on fruit
It affects both acid lime and sweet orange.
Black, mouldy growth develops on honeydew secreted by insect
pests like blackfly, aphids, scalses and mealy bugs.
No parasitism is observed in the citrus, but the presence
of the black matting of mycelium may affect photosynthetic activity.
Affected young fruit do not develop because of the black coating.
The trees look sickly.
Control of homopteran insects (honey dew secreting insects)
by spraying monocrotophos or dimethoate combined with Copper oxy chloride
or mancozeb helps in prevention of the disease.
Spraying of diluted glue or a detergent can wash off
the black coating.
In India, this disease is reported to be present in Bangal, Punjab,
Assam, Karnataka, Uttar Pradesh and Andhra Pradesh.
In Andhra Pradesh, it is severe on Rangapur lime.
Lesions on fruit
The lesions on leaves in early stages consist of small semi-translucent
dits, which become sharply defined pustular elevations usually
on the underside, flat or somewhat depressed at the centre.
The opposite surface corresponding to the warty growth shows
a circular leaves often become distorted, wrinkled, stunted
On the fruit, lesions consist of corky projections which often break
Humidity and rainfall play a very important role in the development
Pruning and destruction of the diseased leaves, twigs, branches and
fruits followed by spraying with 0.3% copper oxychloride, 1% Bordeaux
mixture or 0.1% carbendazim is helpful in controlling the disease.
Ikisan - Tristeza or quick decline desease of citrus
Tristeza (or) Quick decline
Quick Decline is a disease caused by the tristeza virus which spreads
through the use of diseased budwood in nurseries, insect vectors, phanerogamic
aphids and parasites like viz., Cassytha and Cuscuta.
Wilting and death of the tree can occur within 2-3 days, hence, the
name Quick Decline.
Tristeza (CTV) stem pit symptom
In acid lime, vein fleckings or clearing and stem pittings
Sweet orange varieties are symptom less carriers but their
susceptible root stock of budlings show stem pits.
Some of the infected trees decline overnight and dry up in
Vein clearing leaf
Virus the causal agent of disease named as Carium Vialoris.
Two strains of tristeza, viz.,(i) the Virulent or fulminate and (ii)
the ordinary type "avirulent" or mild have been recognized.
The former causes sudden wilting and drying of leaves, while the
latter shows a gradual decadence in the condition of the tree.
Among the two strains of virus, one of which is an independent agent
of stem-pitting, while the other, known as seedling yellows.
Tristeza virus is both vector and bud transmissible.
Insect-Vector transmission of the virus by several insects viz., by
Aphis citricides, Toxoptera citricidus, T.aurantii, Aphis gossypii,
Among these Toxoptera Citricidus is widely distributed in
India particularly in Southern India and Assam.
It is rather rare in northern India, where spread of the virus may
be mainly through infected budwood.
Besides insects, the virus can be transmitted by budding, grafting
and by means of dodder.
It is not transmitted through seed.
The disease can be prevented from spreading by the removal of the
parasites, and by the control of aphids (Toxoptera citricide)
infesting the new flushes.
The use of certified sweet orange buildings on Rangpur
lime rootstock offers tolerance to the disease.
For Andhra Pradesh, Maharashtra and Karnataka, Rangapur
lime is recommended as a root stock resistant to tristeza.
For the Punjab region, Jatti khatti, Cleopatra mandarin
and sweet orange are recommended as resistant root stocks.