CITRUS DISEASES

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CITRUS DISEASES:

BY : DAG 01 CITRUS DISEASES

GUMMOSIS (Phytophthora gummosis):

GUMMOSIS ( Phytophthora  gummosis)

Symptoms::

 Symptoms include rotted roots; cracked bark, accompanied by gumming. Water-soaked, reddish-brown to black bark at the soil line. Discolored tissue in the lower trunk. Yellowing, sparse foliage and death of the tree.  Excess soil moisture favors production and spread of zoospores.  Therefore, increased drainage and careful irrigation is an important factor in disease management. S ymptoms:

Diseases cycle::

Phytophthora parasitica  and  Phytophthora citrophthora  are fungal-like organisms that complete their life cycles in the soil. Phytophthora parasitica  is most active at higher temperatures (85-90F) and is prevalent at lower elevations, while  Phytophthora citrophthora  has a lower optimum temperature for growth (75-80F). In wet soils, both of these organisms produce motile spores, known as zoospores, which are attracted to host roots where they germinate and infect root tissue. D iseases cycle:

Manageament::

Phytophthora  foot rot is controlled by use of resistant rootstock, improving drainage, and timely applications of effective fungicides.  Resistant rootstocks are available and should always be considered when choosing planting material. M anageament:

CANKER :

CANKER Xanthomonas campestris pv. Citri

Symptoms::

This is more commonly observed on leaves, twigs and fruits of acid lime than on sweet orange. Initially it shows up on leaves as small, raised translucent spots. 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. On the twigs the lesions appear water-soaked and dark green first and later turn brown. Symptoms:

Diseases cycle::

Canker-infected leaves, twigs etc, serve as the source of inoculum to spread the disease from season to season. 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. Diseases cycle:

Management::

. 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) By using canker resistant varieties. 2. In case of sweet orange, three sprayings at monthly interval should be carried out of, streptocycline 100 ppm or 0.2% Mancozeb in combination with 0.3% copper oxychloride. The first spray should be done when the fruits are marble-sized. Management:

Diplodia gummosis:

Diplodia natalensis D iplodia gummosis

Symptoms::

Profuse gumming on the upper portions of the trunk, branches and twigs is noticed. Gumming may be common at the crotches or branches, the branches break at the crothches. Gum comes out from the cracks developed on the diseased portion. From bark, the infection spreads to wood which dries and becomes discoloured. S ymptoms:

Diseases cycle::

Black pycnidial bodies appear on the diseased bark which gets removed in flakes. The disease spreads through dissemination of pycnidiospores by air, rain and insects. Diseases cycle:

Control : :

All factors which lead to weakening of the trees should be controlled. Any wound or insect damage to the bark, especially on the limbs and forks, should be scraped, cleaned and painted with Bordeaux paste. Gummed portions of affected bark should be removed and the cut surface protected. Spraying with 0.1% carbendazim on the affected limbs and forks is useful to restrict the disease spread. C ontrol :

Tristeza :

Tristeza virus T risteza

Symptoms::

In acid lime, vein fleckings or clearing and stem pittings are observed. 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 2-3 days. Symptoms:

Disease cycle::

Virus the causal agent of disease named as  Carium Vialoris. Two strains of tristeza, viz the Virulent or fulminate and "avirulent" or mild have been recognized. Among the two strains of virus, one of which is an independent agent of stem-pitting, while the other, known as seedling yellows. Insect-Vector transmission of the virus by several insects viz., by Aphis citricides, Toxoptera citricidus, T.aurantii, Aphis gossypii, A.Craccivora, A.spiraecola. Besides insects, the virus can be transmitted by budding, grafting and by means of dodder. D isease cycle:

Control: :

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.  Jatti khatti, Rangapur lime, Cleopatra mandarin and sweet orange are recommended as resistant root stocks. C ontrol:

Greening :

Obligate gram-negative bacterium G reening

Symptoms: :

A characteristic symptom of the disease is the growth of small, leathery leaves with interveinal chlorosis and the distribution of green islands on a yellow area. Leaves drop prematurely. The symptoms are sectorial on the tree. Other common symptoms include lopsided: fruit, with curved columella and aborted seeds. Yield reduces and trees may become barren. Die-back of twigs also occurs. S ymptoms:

Disease cycle::

The disease can be spread by grafting. Two psyllid insects are important vectors of the disease are Diaphorina citri  is found in Asia and  Trioza erytreae  is found in Africa.  These vectors involve in the spreading of the disease. D isease cycle:

Control::

Select certified disease-free seedlings. Temporary suppression of the disease is possible by injecting infected plants with terracycline 500 ppm. Use of disease-free bud wood and protection of new flush from psyllids (Diaphorina citri) mitigates infection. C ontrol:

Mosaic :

M osaic

Symptoms: :

Affected leaves show irregular yellow or light-green patches alternating with normal green areas without reference to the veins. The fruit drop prematurely and the quality is reduced by rugged surface. S ymptoms:

Disease cycle::

D isease cycle :

Control: :

Aphids ( Toxoptesa citricide ) infesting the new flush should be controlled and the parasite  Cassytha  removed along with haustoria to prevent the spread of the disease. Virus-free certified buds must be used for propagation. C ontrol:

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