Oleander knot

The disease is caused by the bacterium Erwinia oleae (often synonymous with Pseudomonas savastanoi pv. oleae). It is a specialized phytopathogen that causes the formation of tumor-like galls on the stems and leaves of its host plant, disrupting normal physiological processes.

The primary host for this pathogen is the oleander (Nerium oleander). The disease is particularly prevalent in Mediterranean climates and greenhouse environments where humidity levels are high and temperature fluctuations occur, providing favorable conditions for the bacteria to thrive.

Symptoms manifest as distinct knots or galls appearing on branches, stems, and leaf petioles. Initially, these galls are soft and light-colored, but as they develop, they become hard, woody, and may develop necrotic fissures, leading to significant structural damage to the plant's architecture.

Environmental conditions such as high humidity, rain, and warm temperatures significantly accelerate the spread of the pathogen. Bacteria are easily disseminated via water splash, wind-borne droplets, and contaminated pruning tools, allowing the infection to move rapidly through a collection of plants.

The economic and aesthetic impact is severe, as the bacteria interfere with nutrient and water transport within the plant. This leads to reduced vigor, chlorosis, dieback of branches, and in cases of heavy infestation, the eventual death of the entire plant, making it a critical concern for nursery production.

• Sterilize pruning tools between plants using alcohol or bleach solutions.
• Prune and destroy infected plant material immediately upon detection.
• Protect pruning wounds with copper-based bactericides.
• Improve air circulation to reduce leaf and stem wetness.
• Select resistant varieties if available in the region.