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23rd August 1998

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Bugging the choking menace

A tiny insect no bigger than a green gram has been introduced to destroy the destructive Salvinia

By Chamintha Thilakarathna.

A blessing turned into a curse. Salvinia, the plant which was imported during the second World War to prevent Japanese fighter craft from identifying waterways, is now choking the canals and has even spread into paddy fields in recent times.

But soon, scientists promise, this curse will see its final curtain.

Deputy Plant Protection Director of the North Western Provincial Agriculture Department, Mr. Ariyadasa Bandara said, "after years of research and failed attempts we have successfully found the answer to the widespread and disastrous salvinia problem."

The answer is a bug. None other than a tiny insect -no bigger than a green gram-called "certobegus salvinis." The vegetarian bug with a life cycle of one year has the tooth for just salvinia. This has made the task of agrarians easier.

In the Northwestern Province where agriculture is the main source of income, fishermen, farmers, industrialists, residents and even stray animals have been badly affected by salvinia.

Everywhere one looks, the slimy green of salvinia is all that meets the eye. The water of the ancient irrigation tanks is polluted as are paddy fields that stretch as far as the eye could see. Even the drainage systems have been badly clogged.

"The damage cannot be measured in money," Mr. Bandara said. He said that salvinia has successfully blocked sunlight from reaching the water- killing water plants, which are the fishes' food. They also drain oxygen from the water and the other living beings cannot compete.

"Salvinia is a plant which necessarily absorbs water. As a result, on paddy fields where it has successfully taken over, there is little or no room for water to remain for the growth of paddy," he said.

According to him, salvinia also releases hazardous gases like Nitrogen Sulphite, CO2 and Methane, into the water killing life underneath. Indirectly this affects the health of residents eating fish from the tanks.

Salvinia has managed to successfully block many of the tunnels and pipelines dismantling the waterways. It has invaded electricity plants, making it difficult for the machines to be handled.

"There are people who have twisted their arms or broken the handles of machines in trying to turn open the machines which have been invaded with salvinia," Mr. Bandara said.

Eighteen year old fisherman Susil Gamini said that the plant is so strong that they are unable to move a boat or use any other means of transportation to get about on the tanks, because the salvinia is so widespread.

The villagers said that many a time, it has posed a threat to the cattle and goats in the area where deceived by the green field outlook the animals who go in search of grass died by drowning. So far, no humans have faced this fate solely because the villagers are familiar with the problem.

R.M.B.Karunaratna, President of the Hangilikolawatta Nawagaththa Agrarian Services department, himself a farmer said, "farming is affected to a great degree as the plant has spread through the waterways to the fields, cutting the source of water for the paddy and hence affecting the crops."

The Agriculture Department which had tried using several methods to get rid of the "pest' which had taken over at least 50% of the tanks, feel that finally they have found the solution in "certobegus salvinis."

"A three foot layer of salvinia was to be seen before this biological method was introduced. But now we see only a thin layer in the process of disappearing," Mr. Bandara said.

How "certobegus salvinis" works is by eating up the centre and the leaves of the plant. The insect at its worm stage eats the immature leaves then advances to the centre, and attacks the mature leaves once it reaches adulthood. Likewise, it continues to do so completing its life cycle for one year. It also multiplies at a speed of double in two and a half days which has helped scientists to quicken the process. The fascinating thing is that with the destruction of salvinia the insect dies as well for it cannot survive on anything else.

But the department is faced with a small problem of water levels. The water level of the tanks should not go below 2 feet if the insect is to survive to complete its task. The unpredictable climate of the North Western Province which hits hard, at times drying lakes and tanks and at times overflowing them has left the authorities with little or no control over this.

However, they have managed to successfully get rid of at least 40% of the salvinia in the area with the help of villagers. The green in many tanks have started to turn black as the thick layers of salvinia die and sink to the bottom of the tanks.

According to Mr.Ariyadasa Bandara, the plant could actually be used to assist farmers in their agricultural work. "Although Salvinia has turned itself to a nuisance in the area, the plant creates a valuable compost which can be used for coconut plantations for example. This is because once it turns into compost it can reduce the evaporating rate to a large extent. This is a necessity for improving quality and crops of coconut plantations which require a lot of water, especially in the Northwestern Province," he said.

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