Blueberry Phomopsis

The disease known as blueberry Phomopsis is caused by the fungus Phomopsis myrtilli, an ascomycete pathogen that primarily affects highbush blueberries. The fungus overwinters in the infected plant tissues, creating a cycle of reinfection every season. Spores are primarily disseminated by rain splashes and wind, entering the plant through various types of wounds.

The primary host for this pathogen is the blueberry (Vaccinium corymbosum), though other Ericaceae family plants may also be susceptible. The fungus typically invades the stems, causing localized cankers that girdle the branches and eventually lead to the death of the distal parts of the plant, significantly impacting the overall yield.

The most common symptoms include sudden wilting and dieback of young shoots, typically appearing from the top down. On affected stems, reddish-brown to greyish cankers develop. Close inspection of these dead tissues often reveals the presence of small, black, pinhead-sized pycnidia, which serve as the reproductive structures for the fungus.

Development of Phomopsis myrtilli is heavily favored by warm, wet conditions and poor air circulation within the canopy. Factors such as high density of planting, excessive nitrogen fertilization that creates succulent growth, and mechanical injuries from pruning or frost damage make the plants highly vulnerable to fungal invasion.

The economic impact of this disease can be devastating, leading to significant dieback of fruiting wood and overall plant decline. Management requires an integrated approach including aggressive sanitation, where infected canes are removed well below the lesion, along with the application of protective fungicides during the high-risk periods of spring growth.

• Prune out infected branches and dispose of them away from the field.
• Disinfect pruning tools with alcohol or bleach between plants.
• Ensure proper plant spacing to improve airflow and reduce humidity.
• Apply preventative fungicides based on local diagnostic recommendations.
• Monitor fields regularly for signs of stem lesions and wilt.