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Dieback is a condition that afflicts trees and plants, where there are massive die offs of members of the species in a region. The term may be used to describe a number of specific conditions that lead to their death, most notably the Phytophthora dieback that plagues regions around the world, particularly Australia. Dieback may also refer to Eutypa dieback, which plagues grapes throughout the world. The term may also be used more generally to refer to massive die offs caused by things like acid rain or pollution.
Phythophthora dieback is caused by a genus of protists in the water mold group. Each particular pathogen goes after a different species of plant, and they are responsible for some of the greatest blights in the world. Phythophthora dieback has caused massive famines, eradicated huge swaths of forest, and altered the natural landscape in some areas irreversibly. The name phythophthora means literally “the plant destroyer,” and it is the most feared group of pathogens among arborists.
The Great Irish Potato Famine of 1845 was caused by a dieback inflicted by Phythophthora infestans, also known as the potato blight or late blight. It wiped out the staple potato crop, leading to the deaths of more than a million people by starvation, and the emigration of another two million people. This particular phythophthora made its way from Mexico, via the United States, with a shipment of potatoes on their way to Belgium.
Phythophthora ramorum is another dieback pathogen with a massive impact on the world. It is responsible for a phenomenon known as Sudden Oak Death, which has ravaged the forests of Oregon and California. The pathogen causes large cankers to break out on the tree and the leaves to experience a massive dieback, eventually leading to death. Detecting Sudden Oak Death has proven quite difficult, but methods are improving, and preventative treatments are being developed to try to stem the tide before the oak forests are entirely eradicated.
Throughout Australia the species phythophthora cinnamomi runs wild, eradicating huge regions of forest and plant life. The pathogen spreads through subterranean water flows, moving about three feet (1m) a year. Nearly half of the flora in Western Australia are susceptible to dieback, and it is a major environmental catastrophe. It has economic impacts as well, targeting many agricultural crops, such as avocados, grapes, roses, peaches, apples, and apricots.
Eutypa dieback, more commonly known as dead-arm, is a type of dieback that targets grapes. It causes a canker on the grape vines, which eventually lead to the arms of the vines dying, leading to its name. The more common form of dead-arm is caused by eutypa lata, but sometimes a similar condition will be referred to by the same name, although it is caused by phomopsis viticola. Traditionally, grape growers have battled eutypa if it makes an appearance in their vineyards, as it can lead to the death or thinning of many vines; in recent years, however, a number of wine makers have found the taste of eutypa infected grapes quite pleasing, and so have supported it to create wines like the popular d’Arenberg Dead Arm Shiraz.