Nikica Ogris, Thomas Cech
Fig. 1. Canker on oak caused by Stereum rugosum
Fig. 2. Canker on beech caused by Stereum rugosum
Fig. 3. Fruiting bodies of Stereum rugosum
Symptoms of this disease are flask- or club-shaped swellings and mostly one-sided depressions in the lower part of the stem. Later on, the bark splits and dies. The infection usually starts from a dead branch stub which is usually located in the centre of the lesion (Fig. 1). The most obvious indication of the presence of a Stereum canker is the appearance of the closely appressed, irregularly shaped, crust-like fruit bodies on the killed bark (Fig. 3). They are grey-brown, later ochre and their multi-layered hymenium becomes stained blood red when injured (thus an old synonym is Haematostereum rugosum). Their surface is initially smooth, becoming cracked with age.
On oaks (Quercus sp.), beech (Fagus sylvatica), and also hornbeam (Carpinus betulus) at warmer sites with ample rainfall and high relative air humidity.
Widespread in the Danube region but with relatively low frequency.
Causes perennial canker – the margins of wound tissue formed by the tree are repeatedly killed by the fungus during the dormant season so that a broad, open lesion develops. In the vicinity of the lesion, a white rot also appears, but this is demarcated by an effective reaction zone and so usually penetrates only a short distance into the softwood.
Other species of Stereum, e.g. S. sanguinolentum, which has an epidermis of yellowish grey, and grows exclusively on conifers; S. gausapatum, has a generally curved surface and is found on oak barrels.