Circular Leaf Spot Disease

Although it was suspected to be the Pestalotiopsis leaf disease at the beginning it has now been positively identified as the circular leaf spot disease (CLSD) by the Rubber Research Institute of Sri Lanka.

Therefore, the damage it can do to the industry is not to the extend it happened in Malaysia, India, Thailand, Cameroon and Papua New Guinea. The delay in identifying the leaf disease at RRISL could be due to the acute shortage of relevant scientists. It is reported that there are about 25% vacancies exist in addition to not having a Director to RRISL although the RRISL is the first rubber research institute in the world. The GDP contribution from the rubber industry was 0.2 in 2021.

This has led to poor or impossibility of undertaking succession planning which is a greater threat to the entire rubber industry, which is growing rapidly, and the rubber-based industries are heavily dependant on natural rubber latex produced locally. Especially at a time when the country is short of forex.

The rate of spread of the CLSD is not well established. This is serious as no one could rule out a probability of reaching the levels of economic threshold without real time data on factorial effects. The impact on different clones, rainfall, relative humidity, health of the tree, soil nutritional levels, production statistics at regional level and the details of other threatening diseases such as white root disease have to be maintained using technically competent employees of different departments supporting the rubber development of Sri Lanka.

The claims such as a 30% crop loss from the national production due to CLSD in the previous season cannot be justified without real time data. The rubber prices are reaching all time high levels and more than 20,000 hectares that has been abandoned previously due to poor prices have been harvested since last season. It is difficult to ascertain if there is an actual crop loss due to CLSD and the extra crop that was harvested from the abandoned areas have covered the deficit that may have been due to CLSD.

The absence of a permanent sampling method of the leaf fallen on the ground due to CLSD on a daily basis is another shortcoming in the system as the reality and the scope of the problem is not identifiable by default.

The disease triangle (Host, Pathogen, and the environment)

The scientists have been doing their best even with limited resources, manpower and due motivation to control the leaf disease last season. The scientists of the RRISL deserve a bouquet of flowers for that. But the needs must be closely monitored, identified and fixed at the earliest to thwart a national disaster in rubber industry that can happen if there is a short supply of latex.

Host

It has been recorded in Indonesia that the RRIC 100 is somewhat resistant to a similar leaf disease called Pestalotiopsis or commonly known as Pesta leaf disease. Similar studies have been undertaken in Sri Lanka as well, but conclusive decisions are yet to be made.

The national production of natural rubber latex is on a downward spiral as shown in the chart below.  This can decline further without real time digital platform to detect factorial effects.

If arrangements have been made to install a digital platform and millions of Rupees have been paid to the contractor already, arrangements have to be made to get them to complete the job soon.

The pathogen

Two pathogens have been identified as the disease-causing fungi and inorganic fungicides to control the pathogen are in use. The large-scale rubber plantations use drones to undertake the aerial spraying effectively to control CLSD. The small holders who are the majority stake holders of natural rubber farming in Sri Lanka need help as otherwise the possibility of them turning towards alternate short-term crops will not be able to stop.

It is interesting to note that the organic fungicides are being tested by small holders successfully already. Since the private labs may not disclose their herbal formulas it is important to the Ministry to interfere and do the justice without further delay as organic inputs don’t cost us forex at this crucial juncture.

Environment.

Number of climatic factors starting from rainfall patterns, relative humidity, wind speed, colder nights, warmer daytime, daylight duration and even soils seem to have impact on the breeding of the pathogens. The data must be captured at situ and analysed using modern software such as MS Power BI that’s available for free to identify relationships that can be proactively used to minimise possible damages from leaf diseases.

The strains must be made stronger wherever bio fertilizers are used to improve plant immunity and tree health. The RRISL has already recommended methods to avoid high humidity that helps breeding of pathogens fast.  Considering the looming threat of climatic change specially identified to be affecting Sri Lanka, improved agronomic actions are urgent to retain soil moisture, to protect biodiversity by moving away from mono cropping that encourages high cost on weeding as well.

With the rapid changes of environmental factors the country is in need of new Agriculture maps and it is ideally suitable for those who are growing rubber in large scale to move towards areas such as Monaragala and Ampara that have very less impacts on leaf diseases.

The GDP contributions

The ultimate aim should be to produce 200,000 MT of natural rubber latex from our cultivations which is a jump of about 119,000 MT from the current production of 81,000 MT per year. The Ceylon Planters are always ready to shoulder the wheel. Let us put our best foot forward to regain Sri Lanka.

Lalin I De Silva, former Senior Planter, Agricultural Advisor / Consultant, freelance journalist