Phytophthora palmivora is an oomycete that causes bud-rot of palms , fruit-rot or kole-roga of coconut and areca nut. These are among the most serious diseases caused by fungi and moulds in South India. Similar diseases of palms are also known to occur in Sri Lanka , Mauritius , and Sumatra. The causative organism was first identified as Phytophthora palmivora by Edwin John Butler in Phytophthora palmivora produces abundant sporangia on V-8 agar under continuous fluorescent light. However, light is not required for sporangia production on infected papaya fruit.
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Disease Management. Areca palm is prone to a number of diseases during its different stages of development. Forty fungal species, a bacterium and an algae parasite are associated with areca palm. Yellow leaf disease, a dreaded disease suspected to be caused by phytoplasm, also causes losses to its crop.
Koleroga caused by Phytophthora araceae is one of the major diseases of arecanut. This occurs as an epidemic in the heavy rainfall areas of Karnataka and Kerala. The disease first makes its appearance after monsoon period. The first symptom is the appearance of water-soaked lesions on the nut surface near the calyx. The patches enlarge and nuts darken and they shed in large number. The fallen nuts soon develop whitish mycelial mass all over.
Nuts of all ages are attacked and if unchecked, invade crown causing the leaves and bunches to whither. Sometimes, the infected nuts may not be shed and remain mummified in the bunches. If monsoon is prolonged, give a third spray. Use Rosin soda adhesive to ensure tenacity of the spray deposit on treated subtrate.
Remove and burn all fallen nuts since they act as a source of inoculum. Anabe or foot rot. This disease is caused by fungus, Ganoderma lucidum. Symptoms of the disease are akin to that of the draught. The initial visible symptom is yellowing of outer whorl of leaves which gradually extends to inner whorls followed by wilting and drooping. The development of inflorescence and nuts are arrested. Nuts already formed are shed.
At later stages, the weakened crown topples off leaving a bare trunk. All around the base of the palm, brownish patches appear which exude a brown liquid. The interior of the stem at the basal region is discoloured and rotten, emitting a foul smell. The infection extends to roots and gets discoloured, brittle and dry. The fungal invasion interrupts uptake of water and nutrients by the palm, leading to yellow and wilting. Control Measures: Since the infected stumps and roots act as the main foci of infection, strict phyto-sanitary measures are to be adopted by removing and destroying the stumps along with roots.
Isolate affected palms by digging trenches 60 cm deep and 30 cm wide around, away from the base and drench with Captan 0. Before planting. Discourage growing of collateral hosts of the fungus like Delonix regia and Pomgamia glabra.
Bud rot. Bud rot is a fatal disease of areca palms caused by Phytophthora palmivora and characterized by rotting of terminal bud and surrounding tissues and ultimately killing the palm. Control Measures: In early stages of infection, scoop out affected rotten tissues by making longitudinal side splits. Inflorescence die-back.
Button shedding followed by die-back of inflorescence is a severe problem in arecanut plantations. This is primarily caused by Colletotrichum gloeosporiodes.
Control Measures: Removal and burning of inflorescence help reduce the load of inoculum in the field. Aureofungin 50 P at 50 ppm concentration is also effective in controlling the disease. Bacterial leaf stripe. The disease is caused by Xanthomonas campestris pv. The symptoms are purely parenchymatous in nature causing water-soaked linear lesions parallel to the midrib of the leaflets.
The lesions are covered with abundant creamy-white bacterial exudates on the under surface which is a striking feature of the disease. The entire leaflet in a frond may be affected resulting in complete or partial blighting.
In severe cases, entire crown may be affected. When growing buds are affected, death of palm takes place. The disease is aggressive during monsoon. Younger palms years old are highly susceptible. Control Measures: Spraying or stem injection with tetracycline group of antibiotics at ppm concentration is effective.
Stem bleeding. Caused by Thielaviopsis paradoxa, it is prevalent in isolated pockets in all arecanut-growing States of South India. Younger and middle-aged palms are more susceptible. Symptoms appear mostly on lower portions of the stem as small discoloured depressions which later coalesce and cracks develop with the progress of the disease, the fibrous layer disintegrates which hallows up to varying depths and brown gummy exudates oozes out.
Crowns of affected palms get reduced in size followed by reduction in yield. The disease is serious in gardens with poor drainage. Control Measures: Improving the drainage may help in minimizing its incidence.
Scooping out the affected portions and application of coaltar or Bordeaux paste is effective to reduce the incidence.
Yellow leaf disease. The disease is rampant in Kerala and Karnataka. Yellowing of leaves begin in the inner whorl, gradually spreading to the outer parts of the crown. Chlorosis is finally observed on almost all leaves in the whorl from the edges of the individual leaflets to the midrib region.
Withering of the tips starts and gradually spreads to the older portions of the leaf. The freshly formed leaves grow shorter and their laminac show unequal growth and flaccidity. In a few cases, wilting and shedding of leaves are also observed. The nuts are reduced in size, shriveled with their kernels often turning black and there is severe reduction in yield.
Stem of the affected palms becomes spongy and friable, the conducting strands getting destroyed. In advanced stages, the stem breaks off at the top. Rotting of the roots is also observed. Association of mycoplasma-like organisms Phytoplasma with the disease has been confirmed.
Water logging is a predisposing factor in the incidence of the disease. Lack of balance nutrition and unscientific cultivation practices make the palm susceptible to the disease. Control Measures: Since the disease is not amenable to management by conventional plant protection measures, other means of containing the disease should be looked into.
They are:. Adequate drainage should be provided, especially during monsoon season. Phyto-sanitary and plan-protection measures should be adopted to control Anabe, bud rot, spindle bud and mite infestation. Sun-scorching of the stem should be avoided by covering with arecanut leaves or painting with lime slurry.
Application of NPK fertilizers as per schedule along with lime and zinc 8. Nut-splitting is more a physiological disorder than a pathological problem of universal occurrence. It is seen in well-grown, young and healthy palms. The growth of the pericarp does not keep pace with the development of kernel inside, causing splitting up of the pericarp. The split nuts drop and infection of the exposed kernel, renders them useless.
The splitting is due to excess flow of cell sap into the inflorescence in the very healthy palms. Hence, checking of excess flow either by making some deep wound at the base of the spadix or jamming the cells at the base when the nuts are half grown prevents splitting.
Sudden flush of water after a period of drought also results in nut splitting. Potassium deficiency is also a probable cause of this malady. Sun-scorching or stem-breaking. Stem-breaking is another disorder, resulting from prolonged exposure of palms to severe solar radiation. The palms exposed to south west sun are more prone to stem-breaking. Symptoms appear as golden-yellow splits on the exposed side of the stem which turn dark brown and subsequently form longitudinal fissures.
Further colonization by saprophytic fungi weakens the stem and finally breaks. Control Measures: Rising of fast growing trees in the south-west side of the garden protecting stem with dry areca leaves, trailing pepper vines on the stem, and adopting a suitable alignment for planting are recommended measures to minimize the disease.
Pests Management. The arecanut palm is attacked by over 90 insects and non-insect pests which damage the foliage, roots stems inflorescence and nuts. Except spindle bug, mites, root grub, inflorescence caterpillar and pentatamid bug, the damage caused by other pests is not substantial.
Spindle bug Carvalhoia arecae. This is a serious pest multiplying rapidly with close of monsoon. The red and black adults and greenish nymphs colonize the top-most leaf axil at the base of the spindle. The bug sucks sap from the tender spindles resulting in reduction in size of the spindle. The infested portions on the lamina develop necrotic patches which later form shot holes.
Severe leaf damage causes stunting of palms.
Control of fruit rot or koleroga disease of arecanut (Areca catechu L.) 
Disease Management. Areca palm is prone to a number of diseases during its different stages of development. Forty fungal species, a bacterium and an algae parasite are associated with areca palm. Yellow leaf disease, a dreaded disease suspected to be caused by phytoplasm, also causes losses to its crop. Koleroga caused by Phytophthora araceae is one of the major diseases of arecanut.
Control of fruit rot or koleroga disease of arecanut (Areca catechu L.).