Susceptibility of winter cut red pine (P. resinosa) stumps to Heterobasidion root disease (HRD) infection

Heterobasidion root disease (HRD), a destructive disease of conifers, is a growing management concern. Infection by HRD fungus (Heterobasidion irregulare) most often occurs when spores, usually produced when temperature is between 5–32°C, land and germinate on freshly cut surfaces. Older stump surfaces are generally unsuitable for colonization, likely due to changes in chemical and physical properties of wood and competitor fungi which limit HRD infection. Stump protectants are effective but not used or recommended in subfreezing temperatures during winter when spores are less common. This study evaluated the potential for older cut stump infection following snowmelt in spring via inoculation of disks collected 7 weeks following initial thinning and exposed to extensive subfreezing temperatures. We found a surprising number of disks (40%) were successfully colonized with H. irregulare. More research on potential for winter cut conifer HRD infection is warranted as are steps to limit this potential.