Clematis phoma wilt

Pathogen and disease type
Phoma wilt is a serious fungal disease caused by the fungus Calophoma clematidina (syn. Phoma clematidina). It is classified as a destructive vascular and tissue-rotting pathogen that specifically targets the stem and leaf tissues of its host plants, often resulting in rapid wilting and necrosis of the stems.

Host plants
The primary host of this pathogen is the Clematis genus. Large-flowered hybrids are particularly susceptible to this disease. While it primarily affects garden clematis, the fungus can survive in various environmental niches, posing a persistent threat to ornamental collections and professional nurseries.

Symptoms and signs of infection
The most common symptoms include irregular brown or purplish-brown spots on the leaves, which eventually lead to the foliage turning brown and curling. On the stems, the fungus causes dark, sunken lesions, typically occurring near the ground level. These lesions eventually girdle the stem, cutting off nutrient supply and causing the entire vine above that point to wilt suddenly.

Development and severity
The fungus thrives in warm, humid conditions with poor air circulation. It spreads via spores (pycnidiospores) that are splashed onto the plant by rain or irrigation water. The severity of the disease is high, as it can cause significant aesthetic damage and weaken the plant's root system, making the clematis vulnerable to winter damage and eventual plant death.

Protection and prevention measures
Managing Calophoma clematidina requires a rigorous integrated approach:

• Practice strict sanitation by removing and destroying all infected plant debris.
• Ensure proper spacing between plants to maximize air circulation and leaf drying.
• Apply preventative copper-based or systemic triazole fungicides during the early spring growth period.
• Avoid overhead watering to minimize spore dispersal.
• Use mulch to create a barrier between the soil-borne spores and the lower foliage.