Exobasidium leaf and fruit spot

The causative agent of this disease is the fungus Exobasidium maculosum, a specialized pathogen belonging to the basidiomycetes group. It is known to infect plants within the Ericaceae family, particularly targeting commercial cranberry crops. The infection mechanism involves the colonization of plant tissues, leading to localized physiological disruptions.

Cranberry plants are the primary host for this pathogen. The disease impacts various parts of the plant, including leaves, stems, and berries. Given the economic importance of cranberries, the presence of this fungus in a production field can pose significant risks to the commercial yield and overall plantation health.

Symptoms typically manifest as distinct spots on the foliage and developing berries. These spots often start as pale, chlorotic areas that may develop reddish or purplish margins as the disease progresses. During periods of high humidity, a noticeable white fungal growth—comprised of conidia—can be observed on the undersides of the infected leaves.

Environmental conditions play a critical role in the development and spread of Exobasidium maculosum. The fungus thrives in cool, moist weather, which facilitates spore germination and dissemination. Water splash and wind are the primary vectors for moving spores throughout the field, making high-humidity microclimates particularly dangerous for crop development.

The economic impact of the disease is significant, resulting in reduced photosynthetic area due to leaf drop and direct loss of marketable fruit due to spotting and decay. To prevent and manage the infection, growers should ensure good air circulation, monitor water levels in the bogs, and implement a preventative fungicide spray program during the critical stages of plant development.