Coconut plantations face a severe threat in the form of bud rot, a fatal disease caused by the fungus Phytophthora palmivora. This destructive fungus attacks the growing point of coconut trees, rendering them beyond recovery. While bud rot is not widespread in Sri Lanka, occasional minor epidemics have been recorded in wet and intermediate zones. Understanding the symptoms, preventive measures, and control methods is crucial for protecting coconut trees from this devastating disease.

Environmental Factors

Coconut plants aged between 3 to 45 years are particularly vulnerable to bud rot. Similar to other fungal diseases, this condition prevails in high humidity and lower temperatures, providing optimal conditions for the growth and dispersal of the causative fungus (fungal spores). Young plants with clustered leaves and plants shaded by older plants are especially susceptible. The disease is commonly observed in river banks prone to flooding and regions experiencing heavy monsoonal rainfall. Normally, the disease is observed sporadically in widely scattered plants.

Symptoms

Initial Stage

In the initial stage of bud rot, several noticeable symptoms emerge. 

⦿ The spear leaf of the coconut plant loses its lustre and withers, followed by a gradual wilting of adjacent leaves. 

⦿ Close observation of the bud region reveals discoloured patches on the leaves.

⦿ Withered bud turns brown and dry, while lower fronds remain healthy and green.

⦿ Inflorescence drying and immature coconut nut fall are common occurrences at this stage.

Advanced Stage

⦿ As the disease progresses, the spear leaf (bud region) can be easily pulled out and emit a foul odour.

⦿ Subsequently, the bud and a few adjacent fronds fall off, leaving only the trunk-attached fronds. 

Control Measures

To combat bud rot effectively, several control and preventive measures should be followed.

⦿ Infected young plants in advanced stages should be cut and burned to eliminate the fungus. The spread of fungal spores can be reduced by burning infected plants or plant parts.

⦿ Proper management of crop nutrients and moisture is crucial.

⦿ In the early stages of detection, a Bordeaux mixture or a fungicide containing copper can be used. Fungicides containing Dithiocarbamates (5-6 grams dissolved in a litre of water) or Metalaxyl (4 grams dissolved in a litre of water) can be applied to thoroughly wet the bud portion.

To Prevention…

While saving infected coconut trees is challenging, preventing the spread of the disease is possible. Healthy coconut trees surrounding diseased ones can be safeguarded through the application of Bordeaux mixture or fungicide solutions, as well as by using fungicide-containing sacks (Fungicidal bags). If a Bordeaux mixture or a fungicide-containing mixture is used, it is essential to thoroughly wet the apical bud areas of healthy trees every 2-3 weeks.

Preparing Bordeaux Mixture

Ingredients:

⦿ Palmanikkam (Copper sulphate) – 200 g

⦿ Quick lime (Calcium Oxide) – 200 g

⦿ Water – 25 litres

Instructions:

I. Dissolve 200 g of copper sulphate in 5 litres of water overnight or for 12 hours (solution 01).

II.Suspend 200 g of quick lime in 20 litres of water and filter through a fine cloth (solution 02).

III.Then add solution 01 to solution 02 and mix well.

IV.Use the mixture immediately after preparation.

Note: Bordeaux mixture and copper fungicides are toxic. Handle them with care, wearing protective gear.