美国白蜡树面临虫灾威胁(2)
虫虫入侵，美国白蜡树们该如何抵挡？有没有谁来帮帮它们呢？http://t1.g.hjfile.cn/voasp/rm/2007/02/20070227.mp3The United States Department of Agriculture is working to save the ash tree. So are agriculture departments and university extensions in a number of states.In some places, farmers are using "detection trees." These have an area where bark has been cut away. The area circles the tree and is called a…
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