Gloeosporium leaf spot and stem canker

Gloeosporium leaf spot and stem canker, caused by the fungus Gloeosporium minus, is a significant pathology affecting various berry crops. The pathogen acts as an opportunistic parasite, primarily targeting the stems and foliage, often leading to severe weakening of the plant structure and reduction of photosynthetic activity.

The disease primarily affects cranberry (Vaccinium macrocarpon) plantations. In these crops, the fungus manifests itself by attacking leaf tissues and stem cambium. The ability of the pathogen to form cankers on stems makes it particularly damaging, as it disrupts the vascular system, preventing nutrients and water from reaching the fruit-bearing shoots.

Initial symptoms are characterized by small, chlorotic to necrotic lesions on the leaves, which gradually enlarge and become dark brown or greyish. On stems, the disease progresses into visible cankers or open lesions that may girdle the stem, causing the distal part of the branch to wither and die. Spore masses are often visible as small, moist acervuli on the infected surfaces.

The development of Gloeosporium minus is heavily influenced by high humidity and moderate temperatures. The fungus typically spreads through rain splashes, wind currents, and contaminated harvesting equipment. The persistence of the fungus in fallen leaves and dead wood allows it to survive throughout the winter, initiating new cycles of infection in the spring.

• Monitor fields during high humidity periods.
• Ensure adequate drainage and aeration.
• Sanitize equipment to prevent cross-contamination.
• Remove and destroy severely infected plant material.
• Apply fungicides as part of an integrated pest management (IPM) program.

Proactive management is essential for long-term health of the field. Maintaining vigorous plants through proper nutrition and water management significantly reduces the severity of the disease. Fungicide applications should be timed to coincide with high-risk weather conditions, particularly during the early growing season or pre-bloom stages, to protect new growth from early infection.