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    Swiss needle cast is caused by a fungus native to the Pacific Northwest. Its host is Douglas-fir, an iconic evergreen tree in the region. The fungus does not kill its host, but it adversely affects the tree's growth. The fungal fruiting bodies block the stomata, small openings on the underside of the needle where carbon dioxide, water vapor, and other gases are exchanged. As more stomata become blocked, there is a corresponding reduction in photosynthesis this means the tree produces less carbohydrates necessary for growth.

    Scientists with the Pacific Northwest Research Station and their collaborators conducted a study to learn how Douglasfir survive even when exhibiting severe Swiss needle cast symptoms. They found that trees allocate available carbohydrates toward growing new needles and branches at the expense of sustaining trunk growth.

    Aerial surveys of western Oregon show that Swiss needle cast has spread in the past two decades. Earlier studies suggest this increase to be a result of warmer winters and wetter springs. To better understand this relationship, the scientists analyzed tree rings of diseased trees and found that the previous year's relative humidity affects the severity of Swiss needle cast symptoms in following years.

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    Watts, Andrea; Meinzer, Frederick; Saffell, Brandy J. 2014. Fingerprints of a forest fungus: Swiss needle cast, carbon isotopes, carbohydrates, and growth in Douglas-fir. Science Findings 167. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 6 p.


    Swiss needle cast, Douglas-fir, epidemiology, Frederick Meinzer

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