Bull's eye rot

Bull's eye rot, scientifically known as infection by Neofabraea vagabunda (formerly Gloeosporium album), is a significant fungal disease affecting apple and pear orchards worldwide. This pathogen is particularly notorious for its ability to remain latent during the growing season, only to manifest as significant fruit decay during cold storage, causing heavy economic losses for producers.

The host range of Neofabraea vagabunda primarily includes pome fruits. The fungus behaves as a necrotrophic pathogen, colonizing not only the fruit skin but also the bark of the host tree. On the branches, it creates persistent cankers and ulcerations that serve as the main inoculum reservoir, allowing the fungus to survive throughout the winter and persist in the orchard environment for many years.

The diagnostic symptoms on fruits are characterized by circular, depressed, and firm brown lesions. As the infection progresses, creamy-colored or white fruiting structures (acervuli) appear in the center of the lesion, often arranged in concentric rings, which gives the disease its common name, "bull's eye rot." The underlying flesh remains firm initially but eventually becomes discolored and bitter in taste.

Environmental conditions play a critical role in the disease cycle. The pathogen thrives under cool, wet conditions, especially during the late summer and early autumn. Rainfall events facilitate the dispersal of conidia from the cankers on branches to the developing fruit. Orchard management practices such as high humidity and poor airflow due to excessive foliage increase the risk of an outbreak significantly.

Integrated management is essential for controlling Bull's eye rot. This includes strict sanitation programs to remove and burn infected branches, which reduces the primary inoculum load. During the growing season, a robust fungicide program, particularly targeting the period close to harvest, is necessary. Additionally, post-harvest hygiene and maintaining optimal storage temperatures are vital to preventing the spread of the fungus among healthy fruit in the storage facilities.