Ringless honey fungus

Ringless honey fungus (Armillaria tabescens) is a destructive soil-borne pathogen known for causing severe white root rot in a variety of woody plants. Unlike other honey fungus species, it does not produce rhizomorphs, but spreads primarily through root-to-root contact in the soil and the colonization of decaying woody debris.

The host range of this fungus is extensive, frequently causing significant economic losses in crops such as apple, pear, avocado, and ornamental shrubs like azalea. Once established in the roots, the fungus advances toward the root collar, effectively girdling the tree and interrupting the vascular supply, which leads to sudden or progressive decline.

Visible symptoms often include sparse foliage, branch dieback, and stunted growth. The most reliable diagnostic sign is the presence of creamy white, fan-shaped mycelial mats found beneath the bark at the base of the trunk or on the main roots. In advanced stages, the infected roots become soft, stringy, and emit a distinct fungal odor.

Conditions favoring the development of Armillaria tabescens include poorly drained, waterlogged soils and the presence of buried stumps or root remnants from previous trees. The pathogen thrives in warm, moist conditions, which allow it to maintain high levels of activity throughout the growing season and colonize nearby healthy roots.

Effective management requires a combination of cultural and preventive strategies. It is essential to remove all roots and stumps when clearing a site, as these serve as the primary inoculum source. Improving soil drainage, avoiding over-irrigation, and maintaining tree vigor through proper fertilization are critical in reducing the susceptibility of fruit trees to infection.

• Sanitize gardening tools to prevent cross-contamination.
• Isolate infected areas by digging deep trenches around them.
• Regularly monitor the root crown of susceptible tree species.
• Avoid wounding the lower trunk during cultivation.