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The earliest external symptoms of basal stem rot of oil palms occur in the foliage, generally after at least half of the cross-sectional area of the stem base has been destroyed. Decay leads to a restriction of water and nutrient supply to the aerial parts, causing symptoms resembling those of water stress and malnutrition (Turner and Gillbanks, 1974). Visual symptoms alone are thus not necessarily diagnostic of basal stem rot, as other factors leading to water stress, such as drought, high soil water salinity or hyperacid soils also cause similar foliar symptoms (Turner, 1981). In young palms, external symptoms of basal stem rot comprise a yellowing or mottling of the lower fronds, followed by necrosis. Young unfolded leaves become chlorotic and may be reduced in length, sometimes with necrotic tips. As the disease progresses, palms may take on a pale appearance, with retarded growth and spear leaves remaining unopened. Similar symptoms are observed in mature palms, with multiple unopened spear leaves and a generally pale leaf canopy. Ultimately, affected palms may die, the necrosis beginning with the oldest fronds and extending to younger regions of the crown. Palms normally die within 6 to 12 months after the appearance of unexpanded spear leaves.
Infection produces a dry rotting of internal tissues at the stem base or root bole and so at any stage in the disease process, the stem or root bole of the infected palm may fracture and the palm will collapse. Characteristic internal symptoms appear as light-brown dry rot lesions of both the stem and bole, occasionally with visible mycelial growth and narrow, dark bands of tissue between the light-brown lesions. Uninfected tissues outside the leading edge of the lesion area are frequently yellow-pigmented, which Ariffin et al. (1989) considered may represent a host-resistance response to infection. Ariffin and Idris (1991c) reported a number of histopathological studies showing that the fungus colonized the cortex, endodermis, pericycle, xylem, phloem and pith of the palm. Infected root tissues are generally friable, with dry and powdery internal tissues. In older roots, the fungus may be observed as a whitish skin-like layer on the inner surface of the exodermis; cortical tissue becomes brown and ultimately disintegrates, whilst the stele appears black. As root tissues will be infected before foliar or stem lesion symptoms are observed, they are often found completely dead and colonised by many saprophytic micro-organisms.
Only after the disease has been long, and therefore extensively, established will basidiomata of Ganoderma appear at the stem base, or originating from infected roots. The position of basidiomata on the stem usually reflects the position of the infected area within the stem. As the basidiomata only appear after internal rotting has extended to the periphery of the stem, there is much variation in their time of appearance after infection. However, once the palm dies, basidiomata frequently appear along the entire trunk, indicative of a more rapid saprophytic colonisation of the tissues. In the case of younger palms, the soft tissues of the expanding stem are rapidly decayed and the appearance of Ganoderma basidiomata rarely occurs before palm death (Singh, 1990).
Early symptoms in coconuts in South Asia comprise a reduction in the size of fruits and nuts, with a wilting and necrosis of lower foliage. Eventually the crown may break off. Patches of dark-brown, water-soaked tissue appear at the base of the stem and extend upwards (stem bleeding), see Rolph et al. (2000). Roots become friable and white mycelial mats occur in these tissues (Peries, 1974). Brackets (basidiomata) can be observed on the ends of cut roots.
For the purposes of this data sheet only control of the disease in oil palms and coconuts is presented.
See Ariffin et al. (2000), Bhaskaran (2000), Flood et al. (2000), Paterson et al. (2000), Sanderson (2000), Sariah and Zakaria (2000) and Seopena et al. (2000).
The identification of diseased palms is crucial to control (Sanderson, 2000) and with the advent of rapid tests, diagnosis may be quicker in future allowing control measures to be implemented at an earlier stage.
Poor drainage, flooding, nutritional imbalances and heavy weed growth have all been reported to be associated with increased basal stem rot incidence in oil palms. However, as there is no evidence of any direct effect, improvement in growth conditions, although beneficial to the palm, cannot be regarded as direct control effects against basal stem rot disease (Turner, 1981).
Mounding with earth around the stem base has previously been attempted, not only to provide additional support, but also to stimulate root production (Turner, 1981). In a number of estates in Sumatra, mounding has become routine practice for all infected palms over 15 years old, prolonging their economic life (Hasan and Turner, 1996). Mounding has been shown to be an economic technique in that the production of only one more oil palm bunch by the diseased palm will pay for the cost of the mounding in Indonesia. However, in Malaysia where mounding was evaluated, the cost-effectiveness of such treatments should be considered since it may take 2 or more years to recover treatment costs (Ho and Khairuddin, 1997). However, these authors tested the benefits of soil mounding in conjunction with surgery and fumigation with dazomet in mitigating the effects of infection and these treatments would be more labour intensive and involve the purchase of chemicals. Ho and Khairuddin (1997) reported that soil mounding with fumigation and soil mounding alone prolonged the productivity of palms, primarily through the physical benefit of preventing the weakened boles from being toppled by wind.
The isolation of symptomatic palms, by digging trenches to prevent possible mycelial spread of the pathogen to neighbouring healthy palms, has been discussed as a control measure since early this century (Anon., 1915; Wakefield, 1920). However, this agronomic practice has generally proved to be ineffective either because the trench depths were insufficient to remove all infected root material (Hasan and Turner, 1998) or because the trenches were not maintained. Also, this control measure could only be applied to visibly diseased palms, with untreated symptomless palms remaining a potential source of infection. This may be improved with the advent of diagnostic techniques. However, economically, the price of palm oil is so low the labour costs to conduct this work especially where there is a high incidence of the disease, are prohibitive in many oil palm plantations.
In addition, this control strategy was based on the assumption that infection occurs by mycelial spread from root to root between neighbouring palms, which has been since been shown to occur only infrequently and over a very localised area (Miller, 1995; Miller et al., 1999, 2000). If Ganoderma spreads by other mechanisms, such as basidiospore dispersal, the isolation of palm root systems would be ineffective regardless of trench depth. Sanderson (2000) discussed disease management in Papua New Guinea, which is based on prevention of the formation of basidiomata (brackets). Infected palms are removed from the plantations, the trunk base and root ring is excavated to a depth of 10-15 cm below ground, and the areas covered with soil to prevent further bracket formation.
The manual excision of infected tissues from lesions in the outer stem tissues of palms was a widely adopted treatment strategy in the 1970s. However, regular inspection to ensure treatment of palms at an early stage of infection, and mixed results in treated palms, led to a decline in the practice. More recently, mechanisation of the procedure has led to a renewed interest in surgery (Singh, 1990), although limitations still exist. This form of treatment is of little use for young palms, where lesions typically radiate outwards from the centre of the stem. Additionally, if basidiomata do emerge in young palms, it is likely that the decay will be too advanced for effective surgery. Palms over 25 years old are very tall, and as a result may collapse after the excision of even small lesions (Turner, 1981). Furthermore, surgery frequently requires repetition, as infection often resurges if lesions are not completely removed.
Due to the variable regulations around (de-)registration of pesticides, we are for the moment not including any specific chemical control recommendations. For further information, we recommend you visit the following resources:
Basal stem rot disease of oil palms has been recorded widely throughout the tropics, most notably in Indonesia and Malaysia. Following the increased planting of oil palms, infection of young palms has been noted for the first time in Papua New Guinea (Orrell, 1996) but is becoming a serious problem in some parts of Papua New Guinea and the Solomon Islands (Pilotti et al., 2000; Sanderson, 2000; Pilotti and Sanderson, 2001).
In South-East Asia, oil palms are frequently planted as a monoculture on areas previously supporting other plantation crops such as rubber or coconuts, or may be planted on areas cleared from primary forest. Smallholder farmers also grow oil palms in mixed cropping systems with other perennials such as coconuts, coffee and cocoa. Basal stem rot of oil palms is now regarded as the most important disease of oil palms in these production areas in Malaysia and Indonesia, and can result in stand losses of between 50 and 85% over the 25-year economic life of oil palm plantings. Furthermore, infection tends to occur at a progressively earlier stage in the life of oil palms, and more frequently, with each successive planting, such that widespread losses can occur in young plantings of less than 5 years old. In replanting after coconut, sporadic cases of basal stem rot can be seen after only 1-2 years in the field (Ariffin et al., 2000).
Darmomo (2000) attempted to estimate the cost of basal stem rot to the Indonesian economy. He estimated 38 million US$ lost annually to the Indonesian economy assuming only 1% diseases incidence but often the incidence is much higher. Darmono (1998) described disease incidence of 51% in some areas of Sumatra.
Basal stem rot infection of oil palms in Thailand remains low (Tummakate and Likhitekaraj, 1996; Likhitekaraj and Tummakate, 2000).