Alternaria leaf spot of pear

Alternaria gaisen is a fungal pathogen responsible for a serious plant disease known as Alternaria leaf spot of pear. This fungus is specifically known for its ability to cause severe damage to both the foliage and the fruit of pear trees, leading to defoliation and significant harvest losses in commercial and private orchards.

The disease is characterized by the formation of necrotic lesions on leaves and fruit. The pathogen belongs to the Ascomycota division and survives the winter season primarily in the fallen leaves or on infected bark. As temperatures rise in the spring, the fungus produces conidia, which serve as the primary inoculum for new infections.

Symptoms initially appear as small dark brown or black spots on the leaves, which gradually expand and merge. A hallmark of the infection is the development of a chlorotic halo around the necrotic spots. When fruit is attacked, the spots turn black and become depressed, eventually rendering the pear unmarketable and susceptible to further rot.

Development and spread of the disease are highly dependent on weather conditions. High humidity, frequent rainfall, and moderate temperatures ranging from 20°C to 25°C create an optimal environment for the germination and spread of spores. During wet summers, the disease can spread rapidly throughout the orchard canopy via rain splashes and wind.

Preventing and managing Alternaria leaf spot requires a holistic integrated pest management approach. Since the fungus overwinters in plant debris, strict sanitation is paramount to reduce the initial inoculum level. Key control measures include:

• Meticulous removal and burning or composting of fallen leaves.
• Pruning to ensure good airflow and sunlight penetration within the canopy.
• Application of copper-based fungicides in the early spring as a preventive measure.
• Systemic fungicide applications during critical growth stages according to local disease forecasting models.