Cultural Control and Sanitary Measures
Disease is more severe when trees are grown in poorer or less optimal conditions of soil and climate, and therefore a species, variety or genotype, which is well-adapted to the location, should be selected for planting (Hahn and Ayers, 1943; Ito et al., 1963; Sylvestre-Guinot and Delatour, 1983).
Canadian regulations on movement and importation of commodities likely to be infected, exempt those non-growing wood materials that are free of bark or that have been heat-treated to kill the pathogen (CFIA, 2008). However, the fungus is capable of infecting the xylem (Blanchette, 2001) and so could be present in logs without bark.
Quarantine regulations in both Canada and the USA are established to prevent further introductions of L. willkommii by importation and its spread from the areas in which it already occurs (CFIA, 2008; USDA/APHIS, 2009). In Canada, these controls relate to “All species, hybrids and horticultural varieties of Larix spp. and Pseudolarix spp., including plants, plant parts (branches, twigs, scions, logs with bark, pulpwood, isolated bark), plant propagative material and seed with debris” as well as firewood, wood chips, bark chips, logs, telephone poles, cants, railway ties, and lumber (CFIA reg D-02-12) (CFIA, 2008).
Host Resistance (incl. vaccination)
No Larix or Pseudolarix species is known to be completely resistant. The Japanese larch (Lachnellula kaempferi) was considered to be resistant in Europe, but not in Japan (Ito et al., 1963). The hybrids, Lachnellula x marschlinsii and Lachnellula x leptoeuropaea are relatively resistant (Sinclair and Lyon, 2005). Susceptibility is increased by lack of vigour (Hahn and Ayers, 1943).
The destruction of infected trees and branches appeared to be effective in eradicating the pathogen in Massachusetts, USA, over a period of 40 years (Tegethoff, 1965). A similar effort was made on Prince Edward Island, Canada (Simpson and Harrison, 1993). The removal and destruction of infected branches is still suggested as a means of control (The Nature Conservancy, 2009), but the effort and equipment needed may be considerable (Tegethoff, 1965).