Rhizina root disease

Rhizina root disease is a devastating fungal infection caused by the ascomycete fungus Rhizina undulata. The pathogen specifically targets the roots of coniferous trees, leading to root decay, systemic physiological disruption, and eventually the death of the host tree.

The disease primarily impacts a wide range of conifers, with species such as spruce, pine, and Douglas Fir being particularly susceptible. The fungus is especially destructive in young plantations where the infection can spread rapidly through root-to-root contact, creating expanding mortality centers within the forest stand.

Key symptoms include chlorosis (yellowing) of the needles, premature needle drop, and a general decline in tree vigor. In advanced stages, the resin flow at the base of the stem becomes excessive. The presence of the fungus is confirmed by the appearance of its distinctive fruiting bodies—wavy, reddish-brown to dark-brown discs that develop on the forest floor, typically near the stems of infected trees.

The development of the disease is highly correlated with soil temperature. The spores of the fungus require a thermal stimulus to germinate, which is why outbreaks are most frequently associated with sites where logging debris has been burned. The heat from fire acts as a trigger, turning dormant soil-borne spores into active pathogens that aggressively attack nearby root systems.

Effective management focuses on stringent preventative measures, primarily avoiding the burning of slash within or near coniferous plantations. Since there are no practical chemical treatments for established infections, silvicultural practices are essential.

• Avoid fires in reforestation areas.
• Monitor young stands for early symptoms.
• Remove and isolate infected root zones to prevent spread.