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Take Xylella, a bacteria that is a plant pathogen. One particular strain, Xylella fastidiosa (I know, it sounds like a Hogwart's spell), is doing severe damage to the olive trees in Europe. The bacteria is native to Costa Rica but somehow made it to Europe. Some believe it arrived in a shipment of landscape plants and others believe scientists intentionally imported the bacteria. In southern Italy, scientists are currently under criminal investigation in Italy as a result of this situation.
Regardless, the presence of the pathogen created a showdown between the European Union and the Italian government. The EU requires that all countries must take aggressive measures to control Xylella fastidious. These measures include cutting down infected trees and the use of pesticides. The Italian courts blocked these measures at the urging of farmers and environmental activists.
Similar problems are occurring with fruit trees around the world. In Florida, for example, a citrus disease is wiping out whole groves. According to this article in The Atlantic, it is unclear if the citrus industry will survive. The state has aggressively cut groves and backyard citrus trees to try to address the problem--with great controversy, just as in southern Italy.
Check out this interesting article on the southern Italy olive tree issue here in Nature.