This disease is common in almost all coconut-growing areas. This disease is common in plantations that have been neglected, primarily due to a lack of proper nutrients for the coconut tree or severe drought conditions. In the past, coconut leaf blight was mainly confined to the wet zone regions of Sri Lanka, but in recent years, the disease has spread to other areas, including the dry zone regions. This is due to the movement of infected plant material and the pathogen’s adaptation to new environments. The disease is also caused by excessive nitrogen levels in the cultivated land and unnecessary reliance on water in the soil. The spread of the disease is through wind and rain, and the good news is that the condition is not fatal to the coconut tree.
Pestalotiopsis palmarum and Bipolaris incurvate are parasitic fungi that cause this disease. The life cycles of the two fungi are similar as they are both fungal pathogens that infect the leaves of coconut trees.
The life cycle begins when fungal spores are released from infected plant debris, such as dead leaves or stems. These spores can be dispersed by wind or water and survive in the environment for extended periods. When the spores land on a susceptible host, they germinate and produce a germ tube. The germ tube then penetrates the plant’s cuticle and enters the leaf tissue, where it grows and colonises the host. The fungus then produces new spores dispersed to new hosts, perpetuating the disease cycle.
Potassium deficiency shows the closest symptoms, but the presence of Rust -coloured spots helps to distinguish it from this disease.
FIGURE 1 – (A) “Pestalotiopsis palmarum” parasitic fungi, (B) Symptoms of Coconut leaf blight,
(C) Symptoms due to Potassium deficiency
• In the early stages of the disease, yellowish-brown spots and greyish spots are observed on the upper surface of mature coconut leaves.
• When examining the lower surface of a coconut leaf with the above characteristics, the spots are invisible to the naked eye, and the parasitic fungus grows as a black fungus.
• These spots are about 10 mm in length and 4 mm in width, and the border around the spots is dark brown.
• Over time, these spots become interconnected and show large brown spots, and the coconut leaves dry up.
• These characteristics are mostly found among the lower branches of the coconut tree.
FIGURE 2 – (A) Diseased Coconut leaf, (B); Yellowish halo, (C) Leaf spots with grey centre
The probability of infection with this disease is quite high in coconut plants in relatively poor conditions. As this damage affects the function of the leaves, the yield can be slightly reduced. But this disease can be easily avoided by following proper cultivation practices.
• If you have stopped fertilising a crop with mild symptoms, start applying a balanced coconut fertiliser mix.
• If a crop is already being fertilised, apply the following nutrients to the tree every six months until the symptoms are reduced.
|Per Coconut seedling||Per Grown coconut tree|
|Muriate of Potash||250 g||500 g|
|Wood ash||5 kg||10 kg|
• If, for some reason, the application of nutrients does not work (which rarely happens), as a fungicide,
– Bordeaux mixture or
– Application of Tebuconazole 250 g/l EW is recommended.
* When using a copper-containing fungicide such as tebuconazole, 4 ml of the same solution can be dissolved in one litre of water and applied once every 2-3 weeks by wetting the leaves.
* Bordeaux mixture can treat many fungal diseases and is easily made at home.
– Raw material,
Copper Sulphate (Palmanikkam) – 200 gms
Calcium oxide (slaked lime) – 200 g
Water – 25 litres
1. Copper Sulphate (Palmanikkam), turn to dissolve in 5 litres of water for about 12 hours. (1 solution)
2. Dissolve burnt lime in 20 litres of water and filter through a fine cloth. (Solution 2)
3. Add solution 1 to solution two and mix well.
– Using the mixture as soon as it is made will give you the best results. Here you can change the amount of the above ingredients about the scale of fungicide you need.
– Fungicides are toxic to the human body, so be sure to use them with caution.
FIGURE 3 – (A) Tebuconazole 250 g/l EW, (B) Bordeaux mixture