Pesta leaf fall disease challenges rubber production

The Planters’ Association of Ceylon (PA) called for urgent and broader collaboration across domestic and regional stakeholders to develop new solutions to combat the unabated outbreak of ‘Pesta Circular Leaf Spot’ disease that is decimating the Sri Lankan rubber industry. 

While regional plantation companies and the Rubber Research Institute of Sri Lanka (RRISL) have actively collaborated to tackle the fungal disease ever since the first cases were reported in 2019, the island’s rubber production has been continuously weakened. 

This has resulted in a 14% drop in rubber production over the past 5 years – raising serious concerns over Sri Lanka’s ability to meet growing demand for one of its leading export crops. In areas most severely affected, rubber latex production has collapsed by up to 30%.

Currently, it is estimated that national rubber production declined by nearly 6,000 metric tons from 2021 to 2022 alone, resulting in an estimated loss of around $ 12 million. In addition to direct lost revenue, the decline in rubber production has caused significant challenges for rubber product manufacturers who have resorted to importation of rubber latex for their production, significantly increasing their cost of production. 

“This year, Sri Lanka’s rubber production is expected to reach just 60 million kg. Urgent action is needed to address these critical threats to the industry. This includes continued research to combat circular Spot Leaf Disease. Sri Lanka is not alone in facing these challenges, and we hope that through a continuing collaboration with global industry players, we may be able to develop more effective and lasting solutions to this challenge. We also call for greater support on key reforms outlined in the Rubber Industry’s Master Plan, and research into biological and mechanical methods to enhance productivity,” PA Chairman Senaka Alawattegama stated. 

The Leaf Fall Disease is caused by a fungal pathogen and impacts rubber plantations by causing defoliation, which reduces plant canopies and affects leaf area and latex production. First reported in Malaysia in 1987 and again in 2003 the disease later spread to various countries, including Sri Lanka in July 2019. 

By the end of that year, approximately 10,000 hectares in Kalutara, Ratnapura, and Galle districts were affected. Effective disease management relies on precise fungicide application. The RRISL has issued an interim recommendation for Management of the Circular Leaf Spot Disease and the industry stakeholders insist that RRISL commences maintaining model and trial blocks with the implementation of these recommendations in order to monitor effectiveness and develop and demonstrate best practices to the industry.

“The PA and in particular those among our membership who are also part of the Task Force and Consultative Committee established by the Government and the RRISL will continue to extend our fullest support in order to combat this disease, and create a lasting solution for RPCs and smallholder rubber farmers alike,” Alawattegama asserted. 

RRISL Acting Director Dr. Susantha Siriwardena noted that Pesta leaf fall disease severity varies by location, and the factors affecting it are site-specific. Key factors contributing to the disease’s spread include weak plantations lacking proper fertiliser and agronomic practices, weather patterns, micro-environmental conditions in individual plantations, poor maintenance of clonal composition, and inadequate plantation sanitation where the pathogen can grow on weeds or other alternative hosts.

“While information from relevant stakeholders on the extent and severity of Pesta leaf fall disease was limited, we believe that over 30,000 hectares, including a buffer zone of 10,000 hectares, has been impacted, as per our assumption in the development of the national plan in 2023,” Dr. Siriwardena noted. 

To address this, RRISL initiated a survey for 2023, aiming to provide an accurate assessment of the disease’s extent by mid-November this year.

RRISL is actively engaged in scientific research and development efforts to understand the disease and its impact. These efforts encompass multiple aspects, from identifying causative pathogens to studying disease incidence and severity factors. Additionally, RRISL is conducting laboratory and field-level studies to test fungicides, evaluate application technologies, and identify disease-tolerant rubber clones.

The institute has identified three rubber clones (RRI100, RRI2006, and Centennial 4) that show relative tolerance to Pesta leaf fall disease. “The information is given to the breeders to involve them in future breeding programs, which is a long-term solution but takes time.”

RRISL recommends a comprehensive set of preventive measures and best practices for rubber plantation owners to mitigate the risk of Pesta leaf fall disease. These practices include short-term, mid-term, and long-term strategies, addressing factors such as sanitation, fertiliser application, clonal balance, and disease management.

Furthermore, emphasis has been placed on collaborations, including rubber production companies, small and medium-sized growers, universities, the International Rubber Research and Development Board (IRRDB), and partnerships with institutions such as the University of Riken in Japan to combat the disease.

“RRISL’s long-term vision for the sustainability and growth of Sri Lanka’s rubber industry involves integrated management strategies to combat Pesta leaf fall disease and address various other factors affecting rubber production. The institute will continue to provide technical knowledge, resources, and support to growers while promoting diversification of rubber clones and ongoing research into disease resistance,” Dr. Siriwardena stressed.