Peach scab

The fungus develops primarily on the surface of plant tissues, forming dark conidial masses. It overwinters as mycelium within the cracks of one-year-old shoots, demonstrating significant resilience to harsh environmental conditions.

In spring, with favorable moisture levels, the fungus resumes sporulation. Conidia are disseminated by wind, splashing rain, and insects, reaching young fruit and leaves, which initiates the primary infection cycle.

Microscopically, the fungus displays olive-brown conidiophores producing unicellular or bicellular spores. These spores serve as the primary inoculum for the spread of the infection throughout the entire growing season.

The pathogen’s growth is highly dependent on temperature and humidity, with moderately warm and humid conditions being the most conducive for its rapid development and spread across the orchard.

Peach scab affects a wide variety of stone fruits, including peaches, nectarines, apricots, plums, and cherries. The disease causes significant damage to fruits, leaves, and young vegetative shoots.

The greatest economic impact is on fruit quality. Affected areas stop growing, causing fruit deformation, surface cracking, and a substantial reduction in market value, making them unappealing to consumers.

Infection of leaves leads to premature chlorosis and defoliation, which weakens the tree and reduces the number of flower buds formed for the following season, affecting long-term productivity.

On young shoots, the fungus creates characteristic lesions, which can act as entry points for secondary pathogens such as bacterial canker or blossom blight (Monilinia).

Extensive crown infection reduces the tree’s overall cold hardiness, which is a critical concern in regions with harsh winters, leading to potential branch dieback.

On fruits, the disease appears as small, circular, olive-black spots. Over time, these spots expand and may coalesce into a large scabby crust that resembles apple scab.

Leaf symptoms appear as angular or rounded spots that are light green or brown. Under high humidity, a velvety layer of fungal spores can be observed on the underside of the leaf.

Infected shoots develop sunken, brown lesions with a dark border. As the disease progresses, these areas may crack, forming noticeable superficial ulcers on the bark.

Deformation of the fruit occurs because the infected tissue loses its elasticity and stops expanding, while healthy tissue continues to grow, causing the fruit to twist and crack.

Cracked areas on the fruit are prone to secondary rot infections, often turning the produce into waste that is unsuitable for processing or storage.

Effective management begins with cultural practices: pruning and destroying infected shoots that harbor the fungus, and removing fallen leaves to eliminate the overwintering reservoir.

Maintaining an open, well-pruned tree canopy is essential to improve airflow and reduce humidity within the tree, which hinders the development and spread of the fungus.

Chemical control using fungicides is vital. Initial applications should be made at the green tip stage, with subsequent sprays timed according to fruit development and weather conditions.

Both contact and systemic fungicides—including those based on copper, sulfur, or modern triazole chemistry—are effective in suppressing mycelial growth and preventing spore germination.

• Maintain spatial isolation between new orchards and old, untreated, or diseased tree plantings.
• Apply balanced fertilization to support overall tree vigor and boost natural plant immunity against pathogens.