Alternaria blotch of apple

Alternaria blotch of apple is a fungal disease caused by the pathogen Alternaria mali. This disease is a significant concern for apple orchards globally, as it primarily damages leaves and fruit, leading to substantial crop losses and tree weakening.

The disease specifically infects various apple cultivars, with susceptibility levels varying significantly between different types of trees. The pathogen survives the winter in infected orchard debris, leaf litter, and sometimes within the bark, emerging when environmental conditions become favorable for growth.

Typical symptoms include small, irregular, dark brown or black spots on the leaves. As the disease progresses, these spots expand, often forming concentric patterns. When the fruit is infected, it displays dark, sunken, necrotic lesions which can eventually rot the entire fruit, often covered in a characteristic velvety-black spore mass.

Warm and humid weather conditions are the primary drivers for the rapid spread of the pathogen. High rainfall, frequent morning dew, and temperatures around 20–25°C significantly accelerate the production and dispersal of conidia by wind and water splashes. Dense foliage often traps moisture, making such orchards more prone to severe outbreaks.

Effective management requires a multi-faceted approach involving cultural practices and chemical control. Growers should prioritize orchard sanitation, including the removal of infected plant material and proper pruning to facilitate airflow. Applying fungicides during critical periods, such as petal fall and early fruit development, is essential to minimize the impact of the disease.

• Regular monitoring of the orchard during the growing season.
• Pruning trees to improve sunlight and air circulation.
• Sanitation measures to remove potential sources of inoculum.
• Implementing a rigorous fungicide spray program.