Pestalotiopsis leaf disease new threat to rubber plantations

Pestalotiopsis leaf disease of rubber is a new threat to the rubber plantation industry on a global scale. 

The Colombo Rubber Traders’ Association (CRTA) said pestalotiopsis leaf fall caused by the fungal pathogen pestalotiopsis has now become a grave threat to the sustainability of the rubber plantation industry in Sri Lanka. Though this fungus has been reported as far back as in early 20th century in the island, it was considered a mild pathogen until recently. It reached epidemic proportions during the monsoon period of 2019, affecting plantations in the Kalutara, Ratnapura and Galle districts. 

Unfortunately, almost all clones are susceptible to this disease, unlike corynespora leaf disease, which affected the clone RRIC 103 at the start and later spread to a few other clones grown in the country as well. High humidity favours the spread of the disease, causing defoliation and a considerable yield loss and ultimately the death of the tree. Unlike in the case of corynespora leaf disease affecting young leaves at the apple green stage soon after the wintering period, this new disease affects even mature leaves in the last quarter of the year. Further RRI scientists have observed a higher tendency of pestalotiopsis fungus to attack leaves already slightly affected by glyosporium-affected leaves.

The disease can be easily identified as it produces circular patches on affected leaves. Sometimes these lesions coalesce to form necrotic areas on leaf surfaces, causing the fall of leaves. This unusual leaf fall should not be mistaken as late wintering and neglected. 

Presently the other countries affected by this leaf disease are Malaysia, India, Thailand, Cameroon and Papua New Guinea. In these countries, the disease is spreading at an alarming rate causing a considerable yield loss. As no resistant clone to this disease has been identified to date, the only hope in managing the disease is by the use of fungicides. Haphazard application of fungicides, however, is of no use in controlling the disease; chemical spraying should be done at the early stages of development of the disease. Unfortunately, proper protocol for fungicide spraying has not been developed yet. Trials are being carried out to use drones for spraying fungicides from a height of five meters above the canopy of trees, to introduce an economical and effective chemical control system. 

The disease may reach epidemic proportions in the coming monsoon period of this year starting from mid-April, and hence all stakeholders are requested to be vigilant about this threat to rubber plantations, and they are strongly advised to get the assistance of scientists of the RRI in any emergency. They will help plantations correctly identify the pestalotiopsis affected trees.