‘Silent Killer’ at work in South

by Prasanna AMARANAYAKE

The coconut tree or the “Tree of Life” is known to have many uses, from its roots to tips, from culinary to non-culinary. They are grown in more than 80 countries with a total production of 61 million tonnes per year. Coconut is widely grown in Sri Lanka and occupies about 450,000 hectares and is an important component in the daily diet of average Sri Lankan with an estimated per capita consumption of 110 nuts per year.

Approximately 80% of the total 2522 million nuts produced in Sri Lanka are consumed locally, while the rest are exported in the form of copra and oil. Several insect and non-insect pests had affected the coconut palm and reduced both quality and the quantity of coconut in the past. In the 1970s the Kumingi pest (Promecotheca) outbreak tried to destroy the coconut cultivation and was successfully controlled by the use of a biological agent. Thereafter, a mite (Aceria guerreronis) pest outbreak was reported in 1997 and was also controlled in the same manner. Minor diseases like fungal, viral or nutritional diseases have hit the coconut cultivation at several times.

The “Weligama Coconut Leaf Wilt Disease” (WCLWD) is a “silent killer”. It has been attacking coconut trees in several areas in the South for the last four years. Dr. Chithrangani Jayasekara, Director, Coconut Research Institute (CRI) said, “This disease was first detected in the Weligama area in late 2006. The pathogen was identified as a phytoplasma. According to the recent sample survey, there are about 360,000 trees affected in Galle, Matara and Hambantota districts. It has caused 45% coconut yield reduction in all three districts.”

Dr. Priyanthi Fernando, Entomologist, Coconut Research Institute said, “We suspect that WCLWD is transmitted through two vectors in Sri Lanka, namely; Proutista moesta (plant hopper) and Stethanitis typica (Laze bug). These two vectors absorb juice from an infected tree and then move on to another, thereby infecting many trees in the process. Suspected vectors host not only in coconut trees but also in banana, cinnamon like trees. This is hard to control because there is no chance to use pesticide due to the nature of disease and the vector. However, indiscriminate pesticide use is not recommended and is highly hazardous to the natural environment’s bio-diversification”

Is it easy to identify?

The early symptoms of the disease are difficult to distinguish from normal palm and an diseased palm. The symptoms are varied around the world. However, the researches done so far have revealed that WCLWD’s symptoms are more or less similar to the phytoplasma-borne disease known as ‘Kerala Wilt’ in India, which is highly prevalent in coconut palms of the Kerala state of India. It is evident that WCLWD has been shown symptoms such as misaligning of leaves, yellowing and eventually withering of leaves plus root rotting. The disease noticeably retards the growth while it is reducing both the vigour and its yield. Fortunately, the speed at which WCLWD spreads is said to be slow as the vectors are not able to fly fast from tree to another.

However, the action of this “silent killer” has been still confining to the Matara, Galle and Hambantota districts since late 2006. Authorized agriculture officials are on high alert in the South over the spread of a disease affecting palms because if it moves into the Coconut Triangle the adverse consequences will be unbearable and will create national scourge.

How can we tackle this?

According to the CRI, the only option available to eradicate this type of phyoplasma disease is to remove and dispose all infected individual plants. In reality, it is impracticable for a crop like coconut which is so extensively planted and essentially bound with socio-economic background of the growers. However, while there are coconut plantations’ owners who co-operate with authorities to take appropriate action against this blooming crisis, there are those who are reluctant to even reveal the real fact to the government officials. This may be either due to ignorance or fear of losing their cultivation plus means of income.

Thus the only possible alternative is managing the crisis by taking precautions to prevent it from being spread to other areas of the country. Meanwhile, it is important to take action to gradually switching the coconut growers in the infected areas for cultivating not only potential alternative crops such as cinnamon, cashew, rambutan, rubber, pineapple and banana but also livestock to compensate their loss of income as a consequence of coconut crop lose and yield reduction in long run due to WCLWD,.

CRI has already realized the depth of the current burden in infected areas and the possible risk of spreading this frightening disease to other areas especially to the coconut triangle. Therefore, it had come out with interim recommendations through consultations of scientists within the institute and outside organizations to combat this scourge. The interim recommendations of CRI are composed of several steps to control WCLWD and to address the burning problems of coconut crop growers in infested area.

Maintenance of a “Disease Free Boundary” and improving quarantine measures were prominent among them.

Systematic quarantine plan was implemented to prevent the spread of disease to other coconut growing areas of the country by demarcating and maintaining a 3-km border as a disease free buffer zone and barring cross border movement of all kinds of palms through law enforcement. The border of the diseased area identified was A 17 road from Galle to Akuressa, Akuressa to Kirinda-Puhulwella through Kamburupitiya, Kirinda-Puhulwella to Walasmulla, Walasmulla to Beliatta, Beliatte and Tangalle.

CRI took action to declare the identified vector as quarantine/dangerous pest in collaboration with Department of Agriculture. legislation was made barring cross boundary transport of any plant material with the risk of carrying the disease by a gazette notification No. 1542/7 dtd. March 24, 2008.

It also introduced steps to guide victimised coconut growers to manage plants in the centre area as it is not practical to destroy all the coconut plants in the affected area, only the unproductive and aged plants will be removed in a phased manner while encouraging them for opting possible alternative crops and livestock in the same lands.

CRI in collaboration with the Coconut Cultivation Board has been organising several public awareness programs, publications and media materials among coconut growers and the general public to highlight the disease and recommended disease management strategies.

When gauging the importance of coconut as one of the major commercial crops in Sri Lanka and the serious threat of spreading this disease to the other critical coconut growing areas especially to the coconut triangle and its adverse impact, WCLWD crisis should be considered as a national priority to be solved. If this fearsome disease spreads islandwide there would not be any hope for salvaging the country’s coconut industry in future. Therefore, cohesive efforts from all responsible stakeholders in the coconut industry and the cooperation of the public are required to eradicate this “silent killer” from the infested areas and prevent possible risk of loss of employment and economic repercussions in future.