The UMass IPM Fruit Loop, led by the apple enthusiast Hawkeye, has returned with a focus on the bitter and intricate world of apple bitter rot. While bitter rot historically occurred sporadically in Massachusetts, it has become increasingly problematic. The pathogens responsible, part of the Colletotrichum complex, have a long history but were only recently identified as causal agents. In the Northeast, particularly in Massachusetts, C. fioriniae is the most commonly identified species causing fruit disease, alongside other pathogens affecting various plants. Understanding the appearance and progression of bitter rot lesions is crucial for accurate diagnosis, especially distinguishing them from other leaf spots.
Differentiating between Colletotrichum complexes is essential due to their varied climatic preferences and disease manifestations. The complexity extends to fungicide resistance, with some species showing resistance to certain chemicals. Despite efforts to manage bitter rot, challenges persist, including the lack of fully resistant cultivars and the evolving nature of pathogen knowledge. Strategies like orchard sanitation and targeted fungicide applications are recommended, but the increasing frequency of extreme rain events adds another layer of complexity to disease management. As the understanding of bitter rot evolves, continuous research and adaptation in orchard practices are necessary for effective disease control.