Coccinonectria leaf blight

Coccinonectria leaf blight is a destructive fungal disease caused by the pathogen Coccinonectria pachysandricola, historically classified as Volutella pachysandricola. This pathogen is a specific threat to Pachysandra terminalis, a popular evergreen groundcover. Left unmanaged, the blight can rapidly devastate large colonies, causing extensive necrosis in dense landscape plantings.

The fungus targets all aerial parts of the plant, including leaves and stems. As an ascomycete, it thrives in environments where plants are crowded and moisture persists on the foliage for extended periods. The disease is characterized by its ability to spread rapidly throughout a patch, turning healthy green foliage into brown, dying masses within a few weeks of onset.

Symptoms initially appear as small, tan-to-brown spots on the leaves, which expand and merge. As the infection deepens, stem cankers form, leading to the collapse and wilting of the shoots. During periods of high humidity, the fungus produces sporodochia, which look like small, salmon-colored or orange cushions on the underside of leaves or directly on the stems.

Environmental conditions are critical for the outbreak of this disease. Excessive rain, overhead irrigation, and stagnant air due to lack of spacing are the primary drivers of spread. The pathogen persists in the debris left on the ground, serving as a reservoir for spores that are splashed onto new growth by raindrops or water droplets during the following season.

Integrated pest management (IPM) is essential for controlling this blight. Cultural practices remain the first line of defense to prevent an epidemic. Chemical interventions using copper-based fungicides or appropriate systemic fungicides can suppress active infections, but they must be coupled with sanitation.

• Remove and destroy all infected foliage and debris from the site.
• Provide adequate spacing to improve air circulation and foliage drying.
• Avoid overhead watering to minimize spore splash.
• Apply fungicides preventively during wet spring weather.