sdu faculty of forestry journal special edition 2009 - Orman Fakültesi

SDÜ Faculty of Forestry Journal
Figure 1. A stand of common ash severely affected by shoot, twig and branch dieback
(Laussa, Upper Austria, July 2007).
The most obvious symptom is dieback of shoots, twigs and branches (Fig. 1).
Shoot dieback is caused by localized necrotic lesions that initially are small, but as
they expand they girdle the phloem and sapwood occlusion occurs, too. When
phloem girdling and sapwood occlusion take place in winter time, shoots do not
flush in spring, however, when they happen during the vegetation period,
simultaneous wilting of leaves above the lesions occurs (Fig. 2A). Leaves then dry,
turn brown to black and remain attached to the shoots for a long time. Elongated,
often elliptical necrotic lesions and cankers in the bark are characteristic symptoms
of ash dieback (Fig. 2B and 2C). These lesions either form around a dead side twig
(Fig. 2B) or occur around a leaf scar (Fig. 2C). On larger shoots, twigs, branches as
well as on younger stems, the tree often defends itself against the pathogen attack,
at least for some time, leading to perennial cankers.
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