Sphaeropsis knot

Sphaeropsis knot is a disease caused by the fungus Sphaeropsis tumefaciens (often associated with Botryosphaeria species). It is a serious condition that primarily affects the structural integrity of trees by inducing the formation of tumor-like galls on stems and branches.

This pathogen has a wide host range, with citrus species being particularly susceptible. However, it can also infect various deciduous trees, causing significant concern in orchard environments where it reduces fruit yields and can lead to the systemic decline of infected plants over several seasons.

The primary symptom is the development of hard, woody, or corky galls on the branches. As these knots enlarge, they can girdle the stems, preventing the transport of water and nutrients to the canopy, which results in leaf chlorosis, twig dieback, and eventually the death of the entire tree.

The disease thrives in humid climates and spreads primarily through airborne spores or water splashes that land on fresh pruning wounds or natural fissures in the bark. Insects and contaminated pruning tools act as common vectors, moving the pathogen from diseased trees to healthy ones very rapidly.

Effective management requires a combination of sanitation and protective measures to minimize the impact. Key strategies include:

• pruning and disposing of infected branches well below the knot;
• sterilizing all tools between cuts using alcohol or bleach solutions;
• applying protective fungicides to pruning wounds;
• maintaining plant vigor through balanced irrigation and fertilization to improve natural resistance.