英语听力—环球英语 655 Fighting Japanese Knotweed（在线收听）

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　　Voice 1
　　Welcome to Spotlight. I'm Liz Waid.
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　　And I'm Bruce Gulland. Spotlight uses a special English method of broadcasting. It is easier for people to understand, no matter where in the world they live.
　　Voice 1
　　Matthew and Susan were to be married. They were buying a new house near London, England. Matthew and Susan looked forward to their new life together in their new home. But a few months later their beautiful home was ruined. Not by earthquake, wind, or fire. It was ruined by a plant! The plant appeared next to the house soon after Matthew and Susan moved in, but in the coming months the plant began to grow through the floors of their house. Their house is now worth only twenty five percent of the price they paid for it. It may even have to be pulled down to enable experts to kill the plant. The plant is 'Japanese Knotweed'.
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　　Japanese Knotweed is a very strong plant. It is so powerful it can push its way up through roads and buildings. It damages walls and breaks through flood barriers. Japanese Knotweed is causing a lot of damage in America, in Canada and in several European countries.
　　Voice 1
　　Japanese Knotweed comes from Japan - but it does not cause problems there because natural enemies keep it under control. In fact it is a useful plant in Japan. People who keep bees value it because these insects feed on it when many other plants are not in flower. And, in the spring, people eat the young stems of Japanese Knotweed as a vegetable. The plant is also used to produce several different kinds of medicines.
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　　In the nineteenth century, plant lovers visited Japan from other countries. They discovered Japanese Knotweed, and they liked it. It was a big, beautiful plant that they thought would look good in their own countries. So, they collected seeds from the plants and took them back to their gardens. But they did not understand the dangers of taking plants and animals from one country to another country. In the case of Japanese Knotweed, these travellers made a big mistake.
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　　Japanese Knotweed can grow a metre in one month. Its roots go down three metres into the ground and spread to seven metres wide. As it grows, it covers other plants and kills them. Japanese Knotweed can grow in any kind of soil. It does not matter how dry or how wet the soil is. It even grows in rivers - blocking the flow of water and causing floods.
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　　Attempts to destroy this problem plant cost well over 200 million dollars every year in the UK alone. If you cut it down it grows again even more strongly. If you dig it up you must remove every single small piece of root from the ground. If you leave even one piece of root just one centimetre long it will grow again.
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　　The best method of control has been to combine several different processes. The first step is to treat the plant with strong chemicals – weedkillers. This kills the parts of the plant above ground. The dead parts of the plants must be burned. Then even the soil the plant grew in must be treated, in order to destroy every piece of root. It usually takes up to three years before the plants are completely destroyed.
　　Voice 2
　　A new Olympic Stadium is being built in London, England. It will be ready for the Olympic Games in 2012. In 2004, Japanese Knotweed was discovered in the area where the Stadium was to be built. The plant was only in a very small part of the area but the situation was very serious. The building work could not begin until the Japanese Knotweed had been completely destroyed. It took a specialist company two years to clear this small area of this problem plant.
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　　British scientists have been experimenting to find a better way to control Japanese Knotweed. They wanted to discover a new method that is faster and less costly. A group of scientists visited Japan to study the plant in its natural environment. They discovered that, in Japan, the plant has two hundred natural enemies.
　　Most of these enemies are insects that eat the plant, or diseases that attack it. However most of these enemies also attack other plants. The scientists identified only two enemies that could be useful in controlling Japanese Knotweed in other countries.
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　　One of these enemies is a very small insect called a Psyllid. This insect feeds only on Japanese Knotweed. The Psyllids do not kill all the plants but they do weaken them. The Psyllids keep Japanese Knotweed under control in Japan - and it does not cause damage to buildings and roads.
　　The scientists have studied this insect very carefully. They have tested it on ninety different plants in the UK. The Psyllid does not seem to eat any of them.
　　The UK government has given permission for tests to begin in three secret places in the UK. The scientists will take very great care to make sure the Psyllids do not escape and spread to other areas. Other countries in Europe are watching the experiments with great interest.
　　Voice 1
　　It is the first time that any European country has used bio-control. Bio-control uses a natural enemy to control a problem plant or animal. But such experiments have been tried in many other countries around the world. Some of these experiments have gone badly wrong.
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　　One example is the cane toads that were brought to Australia in nineteen thirty five. Particular insects attack sugar cane when it is growing. The cane toad is an animal that loves to eat these insects. The problem is that the cane toad also likes to eat almost anything else! Even worse, the cane toad is poisonous. Animals that eat cane toads die. Australia now has a big problem - too many cane toads.
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　　However, the scientists in the UK believe the Psyllids are completely safe because they do not eat anything other than Japanese Knotweed. Many people agree with them. These people think the Psyllids should be brought to the UK as soon as possible.
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　　Other people are very worried about the idea. These people think that the Psyllids will change their behaviour when they arrive in the UK. They think that when the Japanese Knotweed has been destroyed the Psyllids will be forced to find something else to eat. They may then damage other plants.
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　　The scientists who support the experiment say that Japanese Knotweed will never be destroyed completely. They believe the insects will just keep it under control. They believe the Psyllids will not need to eat anything else.
　　If that is the case, Japanese Knotweed could cease to be a problem in the UK. It could even become as useful as it is in Japan!