Impatiens phomopsis blight

The disease is caused by the fungus Phomopsis impatientis, a specialized pathogen that affects the vascular system and structural integrity of its host. This fungus is known for inducing blight-like symptoms, which can lead to significant losses in both commercial greenhouses and private landscapes.

The primary host for this pathogen is the Impatiens genus, particularly popular bedding plants. The fungus colonizes stems, petioles, and occasionally leaves, causing localized lesions that eventually expand and girdle the plant stem, cutting off the supply of nutrients and water.

Early symptoms include dark, sunken lesions on the stems, often occurring near the soil line or leaf axils. As the infection progresses, the tissues may become brittle. One distinct sign of the disease is the presence of pycnidia—small, black, flask-shaped reproductive structures that develop within the dead tissue and release fungal spores.

Development and spread are facilitated by warm temperatures and prolonged leaf wetness or high humidity levels. The spores are typically dispersed through water splashes from irrigation or rainfall. Poor air circulation in greenhouse environments significantly accelerates the transmission of the fungus from infected to healthy plants.

Management requires a preventative approach, emphasizing sanitation and environmental control. Key practices include:

• Removing and destroying infected plant debris.
• Ensuring proper spacing to improve air movement.
• Avoiding overhead irrigation to keep foliage dry.
• Applying preventative fungicides when conditions are favorable for disease.