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Stem diseases

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INTRODUCTION:

Stem diseases are the diseases that infect the stem portion.

E.g. dieback, pink disease and stem canker etc., since the diseases infect the stem portion it affects the movement of water/ nutrient food materials from root to leaves vice versa.

The stem diseases may infect the outer tissues (e.g. stem canker) or it may intrude inside to stem portion (e.g. heart rot ).

If the infection is external it would not reduce the yield much.

If it is severe it kill the entire plant.

Some time the stem disease visible externally as bleeding (stem bleeding) fruiting bodies (e.g heart rot) or drying from tip backwards (dieback)

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Stem canker:The fungus attacks the branches, forming cracks and lesions along the stem.

The affected branch wilts as the stem tissues are killed, arresting translocation of nutrients.

The disease spreads from one plant to another by air borne infections.The perithecia are formed on the infected tissues.

The fungus remains inside the infected tissues beneath the bark and becomes active whenever climatic conditions are favorable.

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Control:

The infected should be cut and destroyed and Athe cut end painted with Bordeaux paste.

Other sanitary measures such as spraying after pruning, protecting the wounds with Bordeaux paste and preventive sprays against insect attack may prevent the onset of the disease.

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Verticilium wilts:

Symptoms:

The infected ones show dwarfing and stunting due to the shortening of the internodes and generally do not flower and fruit.

In the infection takes place after the plan has flowered or fruited, the floral buds and the fruits become distorted, flaccid and finally drop off.

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Verticillium dahlia

Casual organism:

Mode of spread:

The pathogen is soil – borne and the primary inoculums usually consists of the organism in the soil.

Control:

Benlate 0.1 per cent applied as foliar spray as well as soil application is effective in reducing the wilt incidence.

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Gummosis:

This is one of the severe diseases of citrus in almost every country where these trees are grown extensively.

It is found in all parts of India, affecting almost every variety.

There are at least six species of Phytophthora known to be associated with the disease.

They are:

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Symptoms:The disease manifests itself in the form of water soaked large patches on the basal portions of the stem, near the ground level.

The external symptom as are restricted to the basal stem, whereas the infection spreads further.

The external symptom as are restricted to the basal stem, whereas the infection spreads further.

The disease spreads in both directions in the stem, reaches the main branches and the roots.

Soon these patches turn brown and the bark may split, through which a gum like ooze exudes.

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Stem gall:

Symptoms:

It appears in the form of tumor like swellings on the veins, leaf stalks, peduncles and other above ground plant parts.

The swelling gradually enlarge and reach the size of about 2 cm long and 0.5 to 1 cm broad.

The infected plants are stunted, and when the inflorescence is attacked seed production is reduced considerably.

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Casual organism: Protomyces macrospores

Control:

There is no effective method of controlling this disease, except to adopt field sanitation practices and destroy the diseased plants.

Infested seeds having galls should not be used for sowing.

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Stem bleeding:Symptoms:This is a common disease of coconut and areca nut in many parts of South India.

It is characterized by reddish brown ooze, from the stem cracks, which dries up to form a black crust.

When diseased trees are examined by scooping the infected tissues, the infected portion is seen discolored yellowish brown.

Except the vascular bundles the other tissues are disintegrated and often large cavities are formed in the diseased stem.

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Control:

In the case of new infections, the disease is controlled by scooping out the diseased tissues and sterilizing the open wound with the heat of a burning torch of coconut leaves, followed by the application of hot tar to the surface, after which the cavity is filled with saw dust and tar.

The same treatment may be applied to areca palms affected by the same fungus.

Bordeaux paste or mercurial fungicide is also applied.

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Die back:Symptoms:

The symptoms begin with die back of small branches and twigs, yellowing of leaves and heavy bearing of small fruits.

As the disease progresses the symptoms intensify, resulting in severe chlorosis and mottling, reduction in leaf size and number, and wilting.

After 7-8 years the plant may die, by which time there may be no leaf formation, the branches get dried up and the plant appears wilted almost completely.

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Control:Good cultural practices, improvements in the fertility level of soil and good drainage benefit in reducing decline.

The intensity of the disease is substantially reduced by cross protection with milder strains of the virus.

Proper rootstock – scion combination should be used.

Involvement of Phytophthora spp.and Oidium should be avoided by regular phytolactic measures.

Periodical spraying against possible insect vectors. i.e. aphids, should be done.

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Stem canker: Clavibacter michiganese

Symptoms:

The bacterium affects the various above ground plant parts, including the stem, causing canker- like infections.Firstly, light brown streaks appear on the stem and leaf petioles, which turn black and cankerous.When the affected stem or petiole is cut, creamy yellow bacterial ooze is seen.

At times these cankers may deep seated and cover a large portion of the fruit.

On the stem infection starts as water soaked lesions, with a white halo, later turning dark brown, corky and cankerous.

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Control:

The seed borne infection can be eradicated by hot water treatment or by treating the seeds in organo mercurial slurry or 500 ppm of streptomycin solution.

Spraying the plants with 500 ppm of streptomycin, two or three times at the fruiting stage, would also help to reduce the intensity of the disease.

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Mode of spread:

The disease spread through agricultural implements, including cutting knife.

In the field the infection spreads by wind and water.

Control:

Gummosis disease can be controlled by selecting disease free plants, and adopting strict field sanitation practices.

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To sum up

• Stem diseases are the diseases that occur in the stem portion. eg.

dieback, pink disease and stem canker etc., Since the pathogens

infect the stem portion it affects the movement of water/ nutrient

food materials from root to leaves vice versa.

• The pathogen may infect the outer tissues (e.g. stem canker) or it

may intrude inside to stem portion (e.g. heart rot. Some times the

stem diseases becomes visible externally as bleeding (stem

bleeding) fruiting bodies (e.g heart rot) or drying from tip

backwards (dieback)