Balsam woolly adelgid as cause of threatening silver fir cancer disease

Publication Type:Journal Article
Authors:R. John
Journal:Mitteilungen der Deutschen Gesellschaft fuer Allgemeine und Angewandte Entomologie
Date Published:April
:Pissodes pieceae

At present a complex disease threatens the silver firs in Baden-Wuerttemberg. The most striking symptom of this disease is a bark necrosis which usually develops as a consequence of an infection through the balsam woolly adelgid (Deefitsia piceae, Adelgidae; Hemiptera) lasting over several years. Successive pests like the Norway spruce weevil (Pissodes pieceae, Curculionidae; Col.), the bark beetle of fir (European fir engraver beetle/fir bark beetle/silver fir bark beetle) and bark cancer attack the silver firs as a consequence. An important tree species of nature-oriented forestry is thus endangered in Baden-Wuerttemberg, on which big hopes have been placed especially against the background of the naturally and anthropogenically induced climatic warming. The disease primarily occurs in forest stands that are homogeneous as far as age is concerned, the stands are between 40 and 80 years old. The silver firs (Abies alba) are affected in pure stands as well as in mixed stands (often in combination with common spruce). The trunks of the firs are colored white in several sequential years due to the occurrence of Dreyfusia piceae in several succeeding years. As a consequence resin and mucilage flow from branches develops, dead branches and cracks of the bark are further symptoms of the presence of this pest. Following blackening of the trunk arises as an effect of sooty molds. At the same time the cenks of Neonectria are to be found and it comes to further crack formation in the bark. The infestation by secondary parasites such as the Norway spruce weevil and the fir bark beetle leads to fall of the needles in the summer. Afterwards drillings of wood peckers are very soon present. In the final stage it comes to peeling-off of the bark, and particularly at the root collar lots of pupal cells of Norway spruce weevils can be observed. Over a period of two years fir stands were observed, attacked and non-attacked sample trees were taken and stem discs, needles and branches were analyzed. Nearly all trees attacked with balsam woolly adelgid showed a reduced growth in the years 2003 and 2006. These were years with very small precipitation, i. e. years, in which the trees were guessed to have been in water stress. Thus it can be concluded that the phenomenon occurs only in stands that have experienced previous (latent) damage through the periods of aridness in 2003, 2006 and 2009.

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