Abstract:
This study concerns the effect of pre-harvest killing of commercial
sized, forty year old western hemlock (Tsuga heterophylla
(Raf.) Sarg.) on subsequent stump infection by Fomes annosus (Fr.)
Karst. Further evaluations were made on tree drying, loosening of
bark, wood deterioration and rate of crown and cambial death. Findings
on the susceptibility of injection axe cuts to Fomes annosus are
included.
Two herbicides MSMA and Tordon 101 were applied during four
seasons; incubation periods of six, nine and twelve months were
allowed to lapse between treatment and felling.
Epidemiology of Fomes annosus in commercial thinnings of
western hemlock was subject to deliberate prophylactic treatment
by pre-harvest killing of trees with MSMA. At the same time the
trees dried faster, and bark was more easily removed. Wood deterioration
and breakage increased, but at levels tolerable to pulp operations.
The degree of stump infection reduction, drying and bark removal
was directly related to the amount of cambial kill by the herbicide.
Tordon produced variable results, with stump infection sometimes
exceeding that of the control. Furthermore, Tordon injection
axe cuts were found to be highly susceptible to Fomes annosus infection.
The behavior of Fomes annosus is thought to be responsive to
cambial condition. The two herbicides produced different cambial
responses, hence different responses of the pathogen.
