Blueberry stem canker

Blueberry stem canker, caused by the fungus Physalospora corticis, is a destructive plant disease primarily affecting blueberry plantations. As an ascomycete pathogen, it targets the stems of the bushes, leading to localized tissue death and systemic damage to the plant's vascular system. It is considered one of the most critical diseases in intensive highbush blueberry production.

The disease is characterized by the development of small, red-colored lesions on young stems. As the infection progresses, these lesions enlarge, darken to a reddish-brown or black color, and eventually crack, forming a typical canker. Over time, the stems become girdled, which restricts nutrient and water transport, causing the dieback of branches and, eventually, the decline of the entire bush.

The lifecycle of the fungus revolves around the survival of mycelium in the bark of infected tissues during winter. During the spring and summer months, the fungus produces spores (conidia) that are disseminated primarily by rainfall splashes and wind currents. The fungus requires entry points such as microscopic cracks in the bark, leaf scars, or wounds created by insects or mechanical handling.

High humidity and mild temperatures are the primary environmental drivers for the rapid spread of the disease. Inadequate air circulation within dense canopy structures exacerbates the issue by keeping the bark surfaces wet for extended periods, facilitating fungal germination. Furthermore, improper management practices that lead to plant stress significantly increase the severity of the infection.

Control and management strategies focus on preventing the establishment and spread of the pathogen:

• Rigorous pruning and immediate removal of all infected stems, followed by destruction of the debris.
• Strict sanitation protocols for pruning shears using disinfectants to prevent cross-contamination.
• Selection of cultivars known for their resistance to stem canker.
• Timely application of protective fungicides during the early stages of spring growth.
• Maintaining proper row spacing to improve ventilation and reduce local humidity.