Rubber cultivation: Moving Forward Amidst Challenges

The rubber plantations in the Asian continent were first established in Sri Lanka in 1876 by Sir Henry Wickham. The Director of Kew Botanic Gardens in England provided facilities to grow rubber seeds and Sir Henry was successful in transporting the seedlings to Colombo. Rubber is grown in the vast Wet Zone and certain regions of the Intermediate Zone and Dry Zone. Climatic factors of importance for the successful establishment of rubber are rainfall, temperature, evaporation, relative humidity and wind. In Sri Lanka the rubber plantation sector consists of two sub sectors: estates and the small holding sector.

The first research activities related to rubber in the world was established by a group of British planters in 1909 in vintage Ceylon. These simple beginnings paved the way for the establishment of the Rubber Research Scheme in 1913. Rubber is normally grown in Sri Lanka on lands varying from flat to very steep terrain. More than 65% of the plantations are represented by the smallholder sector, being their sole livelihood.

In terms of manufacturing rubber products, primarily tire retreading, began in Sri Lanka in the 1950s and expanded rapidly after free trade policies and investment promotion zones were introduced in the late 1970s. Today, Sri Lanka’s rubber industry consists of two closely interdependent sectors: (1) the plantation industry, including smallholders, which grows rubber trees and harvests latex that is converted into stable concentrates and raw rubbers; and (2) the rubber products manufacturing industry, which converts raw rubber into finished rubber goods. Raw rubber, a natural polymer, is available in natural rubber and synthetic rubber. Natural rubber is obtained from the Heveabrasiliensis tree, which yields liquid rubber polymer.

The value of Sri Lanka’s rubber exports has been increasing significantly. In 1995, export value was approximately US$135 million, and in 2000 it exceeded US$200 million, with rubber products accounting for 87 percent of that value. To grow and retain market share, Sri Lanka’s rubber product industries need access to raw rubber at global market prices. Rubber trees are harvested after 25 to 30 years, when latex yields become uneconomical. Until the mid1980s, felled trees had little commercial value and were used as fuel. In the past two decades rubber wood has become popular in furniture because of its woodworking properties. Major suppliers of rubber wood products are China, Indonesia, Malaysia, Thailand, and Taiwan.

General rubber goods make many products, such as wiper blades, cables, footwear; rubber covered rollers, sporting goods, floor mats; fenders; springs and bearings; earthquake protection and vibration isolators; rubber bands, insulations, flooring etc. Most latex-based products are gloves and other dipped products used in industrial, household, and medical settings, as well as special electrician’s gloves.

Conventionally raw rubber is graded visually according to their colour and it doesn’t represent the technical quality. In particular, higher amounts of poly-phenolic substances and carotenoids increase the colour of raw rubber. Carotenoids and phenolic substances are responsible for yellowish and greyish to blackish colour in crepe, respectively. For industry, natural and synthetic rubbers are considered complementary materials. Natural rubber is preferred for certain applications, such as aircraft tires, for its ability to handle a wide temperature range. Synthetic rubber’s resistance to oils and chemicals is preferred for other applications- ie: petroleum hoses.

Sri Lankan rubber growers face a distress situation because of the inability to control the costs involved in production. Due to increased manufacturing costs involved in tapping and production of rubber sheets, the profits earned by rubber estate owners and farmers are somewhat low. This is also due to the lack of village-level processing centre’s to support the ecosystem. Some are of the opinion that automation of the labour-intensive tasks involved in the production of rubber sheets can solve most of the challenges.

Rubber Research Institute

The Rubber Research Institute was established with laboratories, land for field experiments and a factory to process rubber on a 178 acre estate, namely Dartonfield. By 1942 this was expanded substantially with the acquisition of another 1,000 acres of adjoining rubber estate in Hedigalla. The RRI has been a dedicated stakeholder in supporting and guiding the local rubber industry.

The RRI has an active role to increase productivity to potential levels of the crop, increase national production of NR to meet the increasing demand, optimal and sustainable utilization of land, labour and other resources, maximize domestic value addition to rubber, encourage individual competency and self-development of RRISL personnel, transfer the developed technologies through training and advisory services.

The Genetics and Plant Breeding Department is involved in developing clones with high yield potential combined with all other desirable secondary characters and this programme supported by Expansion of genetic diversity of local breeding pool with adding new genotypes from Non Wickham germplasm and foreign clones. Rootstock nurseries are established every year during the seed fall. The main seed fall in Sri Lanka is around August-September.

Over half of the rubber lands in Sri Lanka are losing productivity because topsoil is being washed away faster than its replacement by natural forces. Vetiver grass is a well-known plant that can be grown as hedges to prevent soil erosion and increase moisture conservation. Weeds may also act as hosts for many pests and diseases of rubber. Weed control is considered important in rubber plantations. Rainfall is of primary importance for the establishment and growth of crops in the tropics. Intercropping is a practice recommended by the Rubber Research Institute to increase the productivity of rubber lands. This is an important indicator affecting the productivity of the smallholder sector. The correct stand per unit land recommended by the Rubber Research Institute is 520 trees per ha.

Threat of disease

A woman collecting latex on the rubber tree plantation.

Rubber trees face many diseases during various weather conditions. Powdery mildew (Oidiumleaf disease), Colletotrichum leaf disease, Phytophthora leaf fall disease, Phytophthora bark rot are common throughout the rubber growing areas. During the past, there were global epidemics like Corynespora Leaf Fall Disease. In addition to fungal attacks, a number of maladies of non-parasitic origin and injuries that are purely of a physical nature can also affect the rubber plant. Colletotrichum leaf disease is another secondary leaf fall disease seen during the refoliation season. This disease occurs throughout the year but it is severe during the Southwest and Northeast monsoon seasons. Phytophthora bark rot has been reported as the only economically impacting panel disease in Sri Lankan rubber plantations. This disease is emerging with the pod set of the plants. The pathogen infects the inner bark and is severe during the monsoon seasons. Virgin bark is the most susceptible to the disease. Root diseases are very destructive and commonly account for the largest number of tree losses during the immature phase of the cultivations. Three common root diseases found in Sri Lankan rubber plantations are White root disease, Brown root disease and Black root disease. Among them white root disease is the most destructive.

The activities that involve labour in rubber cultivation are; field establishment (fencing, lining, holding and planting), maintenance of the holding (weeding and cover crop establishment), fertilizer application and tapping. The type of labour may be either family, hired or both. The correct angle of tapping cut, which promotes maximum latex removal, is 30° from the horizontal plane. RRI recommends that this angle should be marked with a stencil plate at the correct height, which guides the tapper on the angle. Therefore daily tapping results in severe stress to the rubber plants. Fertility levels and other physical properties of rubber growing lands are so low due to replanting rubber four-five times. This also contributes to low yield.

The Government of Sri Lanka has made several attempts to improve the smallholder rubber sector in various ways through Government institutions. This is by forming societies to cater to the smallholders in marketing, improving technical knowhow, providing materials for processing at concessionary rates and improving the smoke house conditions. Labourers constitute a vital input in agricultural production. They are relocating to different parts of the country to earn a better livelihood, adding to the existing imbalance between demand and supply of labourers.

Innovation is needed in plantation management. To combat the impact of rainfall on production risk, we can consider promoting rain guards for rubber trees. The rain guards for rubber trees are effective in protecting latex yields during the rainy season, increasing latex yields by up to 77 percent. The fungus, Phytophthora, which usually grows on leaves and pods enters the fresh cut with water gushing along the trunk of the tree, causing bark rot. The rubber plantations are surviving under many challenges. The industry has been resilient in the past and estate owners and small scale growers remain hopeful of better days ahead.

 

Dr. Sarojini Fernando

A senior researcher Dr. Sarojini Fernando - Head, Plant Pathology & Microbiology Department of the Rubber Research Institute states “The occurrence of Circular leaf spot disease (the newly spreading leaf disease - Pesta) causes gradual leaf fall from May - July to peak the defoliation in October - November. Defoliation causes a decrease in the density of the plant canopy which affects the decrease in latex production. With the report of the new leaf fall disease condition in 2019, the Rubber Research Institute took immediate actions to educate the Extension Staff and the growers regarding the disease, in order to isolate the disease and to limit further spread”.

The disease can be easily identified as it produces circular patches on affected leaves. She further added “In 2019, the disease was detected from the Kalutara district and later by 2020, the disease had affected plantations in the Kalutara, Ratnapura and Galle districts. The disease is severe in wet and humid areas of the country. Concerted research efforts are going on in all the rubber growing countries to find a firm management protocol, till then interim recommendations have been made to control the situation. For this all the good agricultural practices like proper weeding and fertilization, improving the sanitation of the plantations, avoiding over exploitation, and removal of the weak plants which are beyond tapping are useful.

All the growers are requested to collect the fallen leaves as much as possible and burn them carefully to reduce the inoculums potential. Moreover chemical controlling should be adopted when and where needed. There is a threat of this disease spreading to other crops”.

Dr. Fernando added “For the formulation of an effective disease controlling protocol, the first step will be to correct diagnosis, know the causative pathogen and their life cycle characters. No chemical treatment will be effective unless the facts are correctly known. Furthermore, a Task Force has been established to facilitate disease management operations. The Rubber Development Department is providing the fungicides and also the machinery for the smallholder growers. Through training programmes the RRI educate the growers the way to live with the disease. In the light of the above background, RRISL has already made all the possible interim disease management recommendations”.