Lophodermium needle cast of cranberry

Pathogen and type of disease. Lophodermium oxycocci is an ascomycete fungus that causes a specific leaf spot or needle cast disease in cranberries. As a parasitic organism, it feeds on the living tissues of the host plant, disrupting its metabolic functions. It is considered a serious threat to commercial cranberry production due to its potential for rapid spread under favorable conditions.

Affected crops. This pathogen primarily infects cranberry species, including Oxycoccus palustris and Oxycoccus macrocarpus. While the disease is highly host-specific, it can occasionally manifest on related species within the Ericaceae family. The prevalence of the fungus is highest in areas where cranberries are grown in peat-based soils with constant high humidity.

Symptoms and signs of infection. Initial infection appears as small, reddish-brown spots on the leaves, which gradually expand into irregular necrotic patches. Eventually, the infected foliage turns greyish or brown and begins to shed prematurely. The presence of small, black, oval-shaped fruit bodies (apothecia) on the underside of the leaves is a definitive diagnostic sign of Lophodermium oxycocci.

Development and impact. The fungus thrives in cool, wet environments, typically spreading its spores during rainy periods. It overwinters in infected debris on the ground, serving as a primary inoculum source for the following season. The damage caused by this disease is significant, as it weakens the plant vigor, reduces photosynthetic efficiency, and leads to a measurable decrease in berry yield.

Control and prevention measures. Effective management starts with cultural practices:

• Removing and destroying infected plant debris.
• Maintaining optimal drainage to reduce field moisture.
• Ensuring proper spacing to facilitate air circulation.
• Applying targeted fungicides during the early growth stages if the infection pressure is high.