European larch canker

As the name of this disease suggests, the fungal pathogen (Lachnellula willkommii) that is the responsible agent for this disease causes large numbers of cankers to form on the branches and trunks of infected trees. The appearance of cankered areas is the first sign of the disease. Seedlings and young trees are killed through girdling, ie, the cambium around the circumference of the trunk or main branch is damaged. Initially, the cankers, which are caused by lesions of the cambium and result from a scarring process, appear as swellings on the smaller branches or as depressions in the larger branches. The cankers are accompanied by exudations of resin, which can become very abundant. This gives the cankers a shiny, slightly bluish appearance. In addition, during certain periods of the year, fruiting bodies of the fungus appear on or near the cankers. They are white and hairy and resemble small cups with yellow orange centres. Larch needles on the small stems or branches above the cankers wither in the spring or become discoloured early in the fall.

The presence of cankers on the trunk is usually a sign that the disease is in an advanced stage. This is accompanied by a significant loss of foliage.