|
Basal stem rot- Thanjavur Wilt
- Basal stem rot of coconut is known as Thanjavur (Tanjore) wilt in Tamil Nadu. It is also called as bole rot.
- In India the causal agent of basal stem rot of coconut, Ganoderma lucidum was first recorded in Karnataka State by Butler in 1913.
- This disease was noticed in Thanjavur district of Tamil Nadu after the cyclones of 1952 and hence the name Thanjavur wilt. In a limited survey conducted in 8 districts of Tamil Nadu during 1980, the incidence ranged from 2.6 to 13.5 per cent.
- In some of the severely affected gardens in Muthupet and Thambikottai, the incidence is as high as 31.4 per cent. The disease has been reported in India, Malaya, New Guinea, the Philippiness and Sri Lanka. In Tamil Nadu, it occurs in all coconut growing districts.
- It also occurs in parts of Andhra Pradesh, Gujarat, Karnataka. Kerala, Maharashtra and Orissa. While root (wilt) disease of coconut is a major constraint in the production of coconut in Kerala, basal stem rot of coconut is threatening the coconut industry not only in Tamil Nadu but also in the neighbouring States.
Symptoms
- The diseased trees show the following typical symptoms in different parts of the palm viz., stem, leaves, inflorescence and roots.
Stem
- The first visible symptom of the disease is found on the basal portion of the stem. Diseased palm shows exudation of reddish brown, viscous liquid from the basal portion of the stem upto three metres. Discolouration of the stem and internal rotting are commonly noticed upto the height of bleeding (exudation).
- In advanced stages of basal stem rot the basal portion of the stem decays completely.
- Some palms show wilting symptoms without external bleeding. In some trees, the bark of the stem peels off. The fructifications of the fungus can be observed at the base of the tree just above the ground level in diseased palms in the advanced phase or in the bark of dead palms.
Leaves
- In diseased palms the leaflets in the outer one or two whorls show yellowing and drooping. In advanced stages of infection, the remaining leaves droop down in quick succession except the spindle leaf.
- Delayed production of new leaves and reduction in size of leaves are other symptoms. Outer leaves fall off. The spindles become short and do not unfold properly. In some trees, leaves break off near the base along the midrib.
- Under certain conditions, buds show soft rot and emit bad smell. In advanced stage of the disease, the crown is blown off leaving the decapitated stem.
Inflorescence and nuts
- In the diseased trees development of flowers is arrested and button shedding is common. As the leaves of diseased palms droop down, the substended bunches also hand down.
- The quality of kernels from such bunches is poor, in most of the cases nuts are barren. When the disease progress is slow, only very few normal nuts are produced.
- Most of the coconut trees bear profusely just prior to and at the time of initiation of symptoms. In severely diseased palms, nut and kernel weight, water content, copra weight and oil content decrease.
Roots
- Decay and death of finer roots preceeds bleeding symptoms in the them. With the advancement of the disease rotting spreads to other roots and may show rotting in 70 per cent of the total number of roots.
- Production of new roots in a diseased palm is very poor. Root rot was 42 to 75 per cent upto 60 cm soil depth and 17 per cent at deeper layers.
Fungus
- Ganoderma lucidum (Leyss) Karst. Mycelium is hyaline, thin walled, branches with frequent clamp connnections. Chlamydospores are ellipsoid and slightly thick-walled. They may be terminal or intercalary and some time found in chains.
- The fruit body is perennial, stipitate, usually lateral and sometimes sessile, It is corky at first and becomes woody later. Hymenial surface is white or cream at first and turns brown later. Pores are small, round.
- Basidiospores are thick-walled brown, minutely verrucose, truncated at one end
Epidemiology
- The disease appears to spread from a particular focus of infection towards the periphery in a concentric fashion, the annual rate being 0.2 to 4.8 per cent. The spread is mainly through root contact (root graft) between diseased and healthy palms.
- Uncontrolled flood irrigation in the entire field or running irrigation channels along the palm rows where diseased palms exist or repeated ploughing in the affected garden aids in the rapid spread of the disease.
- The disease incidence is more between the months of March and August. In general, bleeding symptoms and number of wilted trees are more during these months.
Management
- Aureofungin-sol 2 g + one g Copper sulphate or 2 ml of Tridemorph dissolved in 100 ml water may be applied as root feeding. The active absorbing root of pencil thickness be selected and a slanting cut is made.
- The solution is taken in a polythene bag or bottle and the cut end of the root is dipped in the solution.
- Forty litres of 1% Bordeaux mixture should be applied as soil drench around the trunk in a radius of 1.5 metre. Neem cake (5 kg/tree can be applied along with fertilizers and Azotobactor (200 g/tree).
- For early diagnosis of Thanjavur Wilt, an EDTA test utilising the root samples has been developed and based on the O.D. values the disease intensity can be detected.
- Disease intensityOptical Density Value Mild-0.18-
0.22 Moderate-0.24 - 0.59 Severe-> 0.59 Healthy palm-0.02
- 0.10 The test is simple and cost effective.
- Intercrop banana to reduce the severity of Thanjavur Wilt.
- Application of phosphobacteria mixed in 10 Kg of FYM is effective in the management of Thanjavur wilt. Five Kg of Neem cake is to be applied in the basins of the diseased tree.
- After one month, one packet of phosphobacteria (200 g) mixed with 10 Kg of FYM is to be applied. This may be done preferably between September and January months and trees should be given regular irrigation.
- In sandy soil, organic matter status of the soil has to be improved. For this, green manure crops may be raised and ploughed in situ or well decomposed farm yard manure at 50 kg per palm has to be applied every year. Only if organic manures is applied,will the fungicides be effective.
Top
Bud Rot
Phytophthora palmivora
- In Tamil Nadu the disease is found in Chengalpattu, Coimbatore, Cuddalore, Villupuram and Vellore Districts.
Symptoms
|
|
- Palms of all ages are susceptible, but it is more severe in young palms of 5-10 years. The first indication of the disease is seen on the central shoot of the tree (spindle).
- The heart leaf shows discolouration which becomes brown instead of yellowish brown. This is followed by drooping and breaking off of the heart leaf.
|
|
|
- With the progress of disease, more number of leaves get affected with loss of lusture and turn pale yellow.
- The entire base of the crown may be rotten emitting a foul smell.
- The central shoot comes off easily on slight pulling.
- The leaves fall in succession starting from the top of the crown.
- The leaf falling and bunch shedding continue until a few outer leaves are left unaffected.
- But within few months the infection leads to complete shedding of leaves, with subsequent wilt and death of the tree.
|
Pathogen
- The fungus produces intercellular, non septate, hyaline mycellium. Sporangiophores are hyaline and simple or branched occasionally.
- The sporangia are hyaline, thin walled, pear shaped with a prominent papillae. Sporangia releases reniform, biflagellate zoospores upon germination.
- The fungus also produces thick walled, spherical oospores. In addition, thickwalled, yellowish brown chlamydospores are also produced.
Favourable conditions
- High rainfall, high atmospheric humidity (above 90 pr cent), low temperature (18-20oC) and wounds caused by tappers and Rhinoceros beetles (Oryctus rhinoceros)
Mode of Spread and Survival
- The fungus remains as dormant mycelium in the infected tissues and also survives as clamydospores and oospores in crop residues in the soil.
- The disease spread is mainly through air-borne sporangia and zoospores.
- Rainfall also helps in spreading the disease.
- Insects and tappers also help in the spread of the inoculum from diseased trees.
Management
- The infected tissues from the crown region should be removed and protected with Bordeaux paste.
- Bordeaux mixture at 1% may be sprayed so as to reach the crown region as pre-monsoon spray.
Top
Grey leaf blight
Pestalotia palmarum
Symptoms
- Initially symptoms develop only on the outer whorl of leaves, especially in older leaves.
- Minute yellow spots surrounded by a greyish margin appear on the leaflets.
- Gradually, the centre of the spots turns greyish white with dark brown margins and a yellow halo.
- Many spots coalesce into irregular gray necrotic patches. Complete drying and shrivelling of the leaf blade occur giving a blighted or burnt appearance.
- Large number of globose or ovoid black acervuli appear on the upper surface of leaves.
Pathogen
- The fungus produces conidia inside the acervuli.
- The acervuli are black in colour, cushion shaped and sub epidermal and break open to expose conidia and black sterile structures, setae.
- The conidiophores are hyaline, short and simple, bear conidia at the tip singly.
- The conidia are five celled, the middle three cells are dark coloured, while
the end cells are hyaline with 3-5 slender, elongated
appendages at the apex of the spore.
Favourable conditions
- Ill drained soils, soils with potash deficiency, continuous
rainy weather for 4-5 days and strong winds.
Mode of Spread and Survival
- The fungus remains in the infected plant debris in soil.
- The disease is spread through wind - borne conidia.
Management
- Remove and burn the infected, fallen leaves periodically.
- Apply heavy doses of potash. Improve the drainage conditions of the soil.
- Spray the crown with 0.25 per cent copper oxychloride or 1 per cent Bordeaux mixture before the onset of rains.
Pencil point
- Affected trees produce fewer and smaller chlorotic leaves.
- The stem tapers gradually and the small crown fails to produce new leaves. Trunk remains barren like a pointed pencil.
Management of Pencil point
- Dissolve 225g each of Borax, Zinc Sulphate, Manganese Sulphate, Ferrous Sulphate, Copper Sulphate and 10g of Ammonium Molybdate in 10 litres of water and apply around the root zone.
Top
Nematode Management
- The burrowing nematode Radopholus similis
- Radopholus similis is the most important nematode pathogen infesting coconut.
Damage symptom
- The burrowing nematode infested plants exhibit general yellowing and visible reduction in growth, vigour and yield.
- The nematodes produce small, enlongate, orange coloured lesions on the creamy white coloured portion of main tender roots of coconut.
- These lesions coalease and cause extensive root rotting. Tender roots become spongy in texture on heavy infestation.
Life cycle
- The nematode takes three weeks to complete its life
cycle from egg to adult at a temperature range of 24-32oC
- All larval stages and females except males are infective.
- They enter into tender roots and feed in the cortical region of coconut.
- It is a migratory endoparasite causing maximum root damage and is capable of spending its entire life in roots.
Management
- Application of phorate 10g @ 10 g a.i./palm.
Top
Root Wilt Disease
Mycoplasma like organism (MLO)
- Coconut root (wilt) disease was first reported in Kerala following the great floods of 1882.
- Since then it has been spreading slowly towards North and South Kerala extending to few gardens in adjoining Tamil Nadu.
- In Tamil Nadu it occurs in Coimbatore, Tirunelveli and Kanyakumari districts.
- In advanced stages of the disease there was 80 per cent reduction in nuts.
- The disease is non-lethal but debilitating.
Symptoms
- The characteristic symptoms are conspicuous bending of middle and outer whorls of leaves, flaccidity (ribbing of leaflets), yellowing and necrosis of leaflets.
- In the diseased zone over 20 per cent of the affected palms succumb to leaf rot disease, rendering deterioration of such palms faster
- Abnormal shedding of buttons and immature nuts, poor setting of nuts, inferior quality of nuts, lack of ability to produce female flowers and a degenerated root system are important symptoms of the disease.
- In diseased palms drying up of the palms and necrosis of spikelets from the tip downwards are other symptoms.
- Most of the pollens are sterile or with low viability.
- The nuts in the diseased palms have thinner husk and the fibres are thin and weak.
Epidemiology
- MLO is spread by lace wing bugs, Stephanites typicus (Distant). Palms of all ages and all soil types are affected, but those of pre-bearing and early bearing stages are more prone to infection. Palms contracting the disease in pre-bearing stage remain unproductive.
Management
- Spray the leaves with
- Monocrotophos 0.05 ml/lit or Endosulfan (1 ml/lit).
- Apply balanced doses of fertilizers (1 kg Urea, 1.7 kg Super phosphate, 1.7 kg Muriate of potash and 3 kg Magnesium sulphate per palm per year in two splits, 1/3 during April-May and 2/3 during September - October for rainfed palms and in 4 splits during January, April, July and october for irrigated palms).
- Apply 50kg of farmyard manure/palm/year.
- Grow green manure crops like Pueraria phaseloides in basin and incorporate at the time of fertilizer application.
- Control the leaf rot disease by spraying 1% Bordeaux mixture or 0.3% (3 g/litre) Copper oxychloride or 0.3% (3 g/litre)Mancozeb.
- Irrigate the palm during summer months at the rate of 600-900 litres of water/basin once in 4 to 6 days.
- Avoid water logging by providing proper drainage during rainy seasons.
Top
Stem bleeding
Ceratocystis paradoxa
- It is one of the mot important disease of coconut and mostly found in Tanjavur and Kanyakumari districts.
Symptoms
- The characteristics symptom is the exudation of reddish brown fluid from the cracks in the stem.
- The fluid trickles down several feet on the stem and the exudate dries up forming a black crust.
- The tissues below the cracks turn yellow and decay.
- As the disease progresses, more area underneath the bark gets decayed and the bleeding patch extends further up.
- The vigour of the tree is affected and nut yield is reduced.
- The tree is not killed out right but becomes uneconomical to maintain.
- In extreme cases, the trees may become barren and die.
Pathogen
- The fungus produces two types of conidia. Macroconidia are produced on conidiophores singly or in chains.
- They are spherical and dark green in colour. Microcondinia are produced endogenously inside the long cells of conidiophores and cell ruptures when mature and release the microcondia in long chain.
- Microconidia (endoconidia) are thinwalled, hyaline and cylindrical in form. C. paradoxa also produces hyaline perithecia with a long neck base is ornamented with knobbed appendages and ostiole is covered by numerous pale-brown, erect, tapering hyphae. Asci are clavate and ascospores are hyaline and ellipsoid.
Favourable Conditions
- Copious irrigation or rainfall followed by drought, shallow loamy soils or laterite soil with clay or rock layer beneath the soil, poor maintenance of gardens and damages by Diocalandra and Xyleborus beetles.
Mode of Spread and Survival
- The fungus survives in the infected plant debris and soil as perithecia and conidia.
- Spread is mainly through wind-bome conidia.
- Irrigation and rain water also help in the disease spread.
- Beetles which feed on the diseased plants also help in transmission.
Management
- The bark of the trunk should be removed in the bleeding area and Bordeaux paste should be applied in this area.
- Preparation of 1% Bordeaux mixture:
- A quantity of 400 g of copper sulphate should be dissolved in 20 litres of water.
- 400 g of lime in another 20 litres of water separately.
- The copper sulphate solution should be added to the lime solution constantly stirring the mixture.
- Earthen or wooden vessels alone should be sued and metallic containers should not be used.
- To find out whether the mixture is in correct proportion, a polished knife should be dipped in the mixture for one minute and taken out.
- If there is reddish brown deposit of copper, additional quantity of lime should be added till there is no deposit in the knife.
- Preparation of Bordeaux paste: Take 200 g of Copper sulphate and dissolve it in one litre of water.
- Take 200 g of lime and dissolve in one litre of water separately.
- Both are mixed simultaneously in a third vessel and the resultant mixture can be used as a paste.
Top
Tatipaka disease (Minor in TN)
- Tatipaka disease is a slow debilitating disease of coconut in Andhra Pradesh and it severely affects the productivity of coconut. Declining yield of coconut trees in Tatipaka village in Andhra Pradesh.
- As the disease was first reported from 'Tatipaka' village, it is known as Tatipaka disease. It is not a serious one in Tamil Nadu.
Symptoms
- Tatipaka disease is found mostly in coconut trees of 20 to 60 years age. At the initial stage of the disease the root growth is vigorous. With the advancement of the disease root growth is reduced. Diseased palms show extensive root rot.
- Root regeneration is highly reduced which results in slow decline of diseased palms. Tapering of the stem below the crown is one of the characteristic features. Diseased trees show twisted trunk or trunk bent in 'S' shape below the crown. Diseased palms have reduced number of leaves. Leaves become small, light green and slowly turn yellowish green.
- In the early stages, only lower leaves show yellowing symptoms. Subsequently all the leaves turn yellow with marked reduction in leaflet size. In some cases, leaflets of some leaves adhere together without normal splitting.
- This gives a fasciated appearance to the leaf. Water-soaked lesions may appear on leaflets of some trees. The fronds instead of bending at the tips as in normal trees, shows a bow-like appearance due to bending at the middle.
- Some fronds are found twisted. The dried up fronds usually hang below the crown instead of naturally falling to the ground.
- The spathes are very small with less number of rachille. Diseased palms produce less number of bunches year after year. In early stages of the disease, normal but small sized nuts are produced.
- With increase in disease severity, number of normal nuts get reduced. Atrophied nuts are found increased in diseased bunches. Some trees may bear only atrophied nuts. Atrophied nuts are small, contain no water and copra and are even without shell.
- They are full of fibre. Some nuts show longitudinal cracks with gum formation. In extreme cases of tatipaka disease, the palms do not produce any nuts and become barren.
- Nuts in diseased trees change from elongated to round shape. Hard mesocarp becomes soft with number of depressions. Water content and copra weight are reduced. Such nuts have very short storage life.
Management
- The disease can be controlled by eradication of diseased palms. Dwarf cultivar, Gangabondam in the disease prone area is found to be free form the disease.
Top
|
