Lachnellula willkommii (European larch canker).

The European larch canker pathogen, L. willkommii, is apparently native to Japan, but established in Europe, where it became well known due to its damage to plantations of exotic and native Larix species, beginning in the nineteenth century. It attacks and spreads among the various species of Larix once it has been introduced. It was detected as an invasive to North America on two occasions; once in the northeastern USA in the 1920s (Hahn and Ayres, 1936) and once in the eastern maritime provinces of Canada in the 1980s (Magasi and Pond, 1982). Efforts to prevent its introduction across natural barriers include regulation and restriction of trade and transport of susceptible species and bark-bearing products made from them. Control by destruction of infected plants or plant parts is often made difficult by the size of the trees concerned (Tegethoff, 1965). Local spread of the fungus between trees appears to depend on dissemination and survival of airborne ascospores. Climatic conditions of humidity and temperature appear to limit natural spread from regions of establishment (Ostaff, 1985).