Uprooting trees and crop diversification:

Formula to halt coconut wilt disease

The Coconut Cultivation Board (CCB) has recommended the uprooting of 400,000 coconut trees affected by the Weligama coconut wilt disease.

Chairman, CCB, J. Gunatilleke said the estimated cost for cutting down these trees is over Rs. 750 million. The disease has reduced the country's coconut yield by over 45 percent.

First diagnosed in late 2006 from Weligama, the coconut wilt disease has since spread to Galle, Matara and Hambantota. Although this disease does not kill the palms, it reduces their vitality and over a one-year period reduces yields by 30 to 40 percent, explained Director, Coconut Research Institute (CRI), Dr. Chithrangani Jayasekara.

Wilting of leaves is one of the initial symptoms of the disease. "The usually triangular coconut leaves become flat and start yellowing." The Director explained that a secondary problem is that trees that have contracted the disease are susceptible to other diseases such as leaf rot disease, which is caused by a fungus. Once this sets in, a drastic reduction of the palm's vigour is observed. It may also kill the tree, explained Entomologist, CRI, Dr. Priyanthi Fernando. The palm is left with fishing rod-like fronds and dies within a year.

Caused by a phytoplasma, the Weligama coconut wilt disease is spread by two vectors - the lace bug and planthopper. The vectors suck juice from an infected tree and move on to another, infecting many trees. "Vector control in this situation is extremely difficult." According to Dr. Fernando, biological control methods are not possible here since no specific predator has so far been identified.

As in the case of the Kerala wilt that has prevailed for over 100 years, no cure has so far been discovered. "Phytoplasma diseases are incurable. No treatment has been found anywhere in the world for any plant species affected by this type of disease", said Dr. Fernando.

Disease-free zone

Since the disease was first discovered in Weligama, a 'disease-free zone', three kilometres wide and 86 kilometres long - from Akuressa, Walasmulla, Beliatta to Tangalle - has been declared by the CRI to prevent the disease from spreading further.

All affected palms from the area were removed and transportation of plants prohibited under Gazette notification. But the disease-free zone has proven to be difficult to maintain due to the illegal transportation of affected plants. "We later observed some plots containing diseased plants outside the zone", said Dr. Fernando.

The second strategy, which commenced on June 17, is to mark diseased trees and issue permits to their owners for the trees to be uprooted and then carry out the uprooting within two weeks. Subsidies of Rs. 2,000, Rs. 1,000 and Rs. 500 are provided for each tree aged between five and 45 years, over 45 and below five which are uprooted within the specified period. A CRI monitoring field team will uproot trees that have not been uprooted by their owners. However, no subsidy will be provided for such trees.

Transportation of timber from the felled trees has been deemed safe and is allowed. "When the tree is uprooted, the germ dies. But the tree's crown has to be destroyed either by burning or burying," explained Dr. Fernando.

Dr. Jayasekara explained that if the affected trees are not uprooted, the disease will spread to other areas. She emphasised the importance of keeping the disease from spreading to the Coconut Triangle. "We see a lot of resistance from plantation owners to uprooting", said Dr. Jayasekara. She explained that it is a debilitating disease. Coconut trees gradually lose vitality and may take years to become unproductive. "People can't really understand why we are trying to uproot the diseased trees as they appear healthy."

Higher subsidy

D. Walawege, who owns the Mulana Estate in Weligama, said the Government should consider giving a subsidy higher than Rs. 2,000 per uprooted tree. "If it concerns a few trees, it would not be much of an issue. But if a large number of trees are uprooted from a single plot, it could have huge economic implications on the planters", Walawege said. "Any alternative, even involving hybrids, may take as long as five years to bring results."

The CRI in collaboration with other departments plans to introduce crop diversification methods to the affected plantations. Cinnamon, cashew, rambutan, rubber, pineapple and banana are among the alternative crops the CRI plans to introduce under this method. They also hope to introduce the affected plantation owners to the livestock business to reduce their economic losses.

Referring to the proposed crop diversification scheme, Director General of the Department of Export Agriculture, W.D.L. Gunaratne said apart from in low-lying areas where water stagnates and areas close to the sea where the salinity is high, the ideal export crop for the area would be cinnamon. "We plan to plant 100 hectares of cinnamon within three years." He also proposed citronella for the drier regions of Matara such as Beliatta.

Although, as Dr. Fernando of the CRI explained, vectors of the Weligama coconut wilt disease are polyphagous and feed on the juice of other plant species such as banana and cinnamon, they do not cause disease in these plants. Since cinnamon will be introduced after the removal of the diseased coconut plants, the germ will not be transmitted to the new plantations.

The Department of Export Agriculture is prepared to assist with technical advice and market links and if the budget is approved by the CRI, planting would also be carried out free. A processing centre and a leaf oil distillation unit for the area are also on the drawing board.

Cinnamon more profitable

"Cinnamon is more economically profitable than coconut", assured the Director General. The first harvest can be reaped after an year and a profit of Rs. 100,000 can be made from one hectare after six or seven years. Cinnamon is not new to this area, he pointed out, claiming that Galle and Matara are two of the leading cinnamon cultivation districts.

Over 65 percent of the coconut trees in the Southern Province have already been affected by the disease, said Research Officer in Charge, Agricultural Research Station at Telijjawila, Matara, Dr. Sujatha Weerasinghe. She reiterated the necessity for planters to collaborate with the CRI to eradicate the disease from Sri Lanka.

The vector

Dr. Weerasinghe explained that a proposal has already been made by the Department of Agriculture to introduce a crop diversification project which is awaiting CRI approval. "Our objectives are to introduce immediate alternative income generation strategies for the affected plantations as well as to introduce economically viable crops as alternatives for coconut", she said.

She said mixed crop cultivation of long- and short-term crops has been identified as the most suitable cultivation pattern for the area. "The main crops will be fruits, but vegetables can be cultivated as inter-crops." Short-term crops include banana, pineapple and guava, which will bear fruit in an year. Long-term crops such as rambutan and mango will provide yields after four years. "In time, these crops will compensate for the income loss which was a result of the wilt disease", said Dr. Weerasinghe.

The Department of Agriculture hopes to introduce crop diversification to every 10 ha that have been cleared. Dr. Weerasinghe explained that once they receive the go-ahead for their proposal, funds can be allocated for the plant material and fertiliser. With labour from the Department of Agriculture or hired labour, they hope to demonstrate how to plant and care for the newly introduced crops.

Alternative crops

"It will not stop with the provision of plants", explained Dr. Weerasinghe. "We hope to also monitor their progress, while providing technical advice." She said although alternative crops have to be maintained, they would generate more income, especially after the long-term crops start yielding, when consistent maintenance is not required. "Besides, the crops introduced don't require much maintenance."

She pointed out that one hectare can accommodate 100 rambutan or mango trees, which would yield 0.5 metric tons. "And if one kilogram is sold for Rs. 25, Rs. 12,500 can be made from a hectare." She also said that short-term crops such as pineapple or banana, from a hectare of 6,000 trees that yields five metric tons, if sold for Rs. 30 per kilogram, could bring as much as Rs. 150,000.

"Coconut can be replanted once the disease is eradicated", said Dr. Weerasinghe. "But our priority should be to stop the disease from spreading further." She claimed that Sri Lanka's coconut production will not be jeopardised, as many fear it would, since the liberated areas in the North and the East will soon venture into coconut cultivation.

Dr. Jayasekara said that the CRI plans to introduce resistant cultivars for which studies are already under way. She explained that the bacteria which causes this disease has a latent period of two to three years.

"After a monitoring period of five years, if we are successful at eradicating the disease through uprooting the diseased trees and crop diversification, it would be safe for planters of the area to switch back to coconut cultivation."

-SP