Managing Dual Disease Issues in Photinia 'Red Robin'

A declining Photinia 'Red Robin' showing black leaf spots and red, drooping foliage likely suffers from two distinct diseases requiring different management strategies.

Black Spot (Entomosporium Leaf Spot)

This fungal disease causes dark lesions on leaves, leading to premature defoliation. Control measures:

• Apply fungicide (chlorothalonil, myclobutanil, or propiconazole) at bud break in spring.
• Repeat every 10-14 days through the growing season.
• Remove and destroy fallen leaves to reduce inoculum.
• Improve air circulation through selective pruning.

Fire Blight (Erwinia amylovora)

The red, drooping leaves suggest this bacterial vascular disease. Management is more challenging:

• Prune out infected branches 12 inches below visible symptoms; sterilize tools between cuts.
• Apply streptomycin or copper-based bactericides during bloom (professional application preferred).
• Avoid high-nitrogen fertilizers that promote susceptible succulent growth.

Site and Cultural Factors

Waterlogged soil in winter exacerbates both diseases by stressing roots and promoting pathogen activity. Improve drainage if possible, or consider relocating to a better-drained site.

With consistent fungicide programs for black spot and cultural management for fire blight, the hedge can be maintained, though severely affected plants may need replacement with resistant cultivars.