Rhizina root rot

The causative agent of Rhizina root rot is the ascomycete fungus Rhizina undulata. This soil-borne pathogen poses a significant threat to young conifer plantations. It is highly specialized, typically emerging in areas where soil has been subjected to intense heat, such as fire sites or former campfires.

The disease primarily targets conifer species, including pines, spruces, firs, and larches. Young trees and seedlings, generally under 15 years old, are the most susceptible to infection. The fungus infects the roots, disrupting the tree's ability to uptake water and nutrients, eventually leading to death.

Symptoms of the infection manifest as the yellowing and browning of needles, starting from the tip of the tree. A distinctive diagnostic feature is the presence of the fungus's fruiting bodies. These appear as dark brown, wavy, disc-like structures with a white margin, often found on the soil surface at the base of the infected trunk.

The development of Rhizina undulata is strictly dependent on heat stimulation. The fungal spores remain dormant in the soil and require exposure to high temperatures (typically from campfires or controlled burns) to germinate. Once activated, the mycelium spreads through the soil to the roots of nearby living trees.

The impact of this disease is severe, often resulting in localized tree mortality that can expand rapidly through a plantation. Effective management and prevention strategies include:

• Strict prohibition of campfires in or near young conifer stands.
• Timely removal of infected trees and surrounding soil to prevent mycelial spread.
• Monitoring plantation sites for the appearance of fungal fruiting bodies.
• Avoiding fire usage during site preparation for new plantings.