Peach scab

Peach scab is caused by the fungus Cladosporium carpophilum, which belongs to the phylum Ascomycota. It is a common pathogen affecting various stone fruits.

The fungus overwinters as mycelium in lesions on twigs and branches. As temperatures rise in spring, it produces spores that are spread by rain splash and wind.

The pathogen requires high humidity and warm temperatures (18–25°C) for optimal spore germination and colonization of host tissues.

The latent period between infection and the appearance of visible symptoms can range from several days to a few weeks, depending on the environment.

Repeated cycles of secondary infection throughout the summer allow the disease to build up rapidly if conditions remain favourable.

The primary hosts include peaches, nectarines, apricots, and plums. The disease can affect fruit, foliage, and shoots, causing significant economic losses.

Fruit quality is severely impacted, with spotted and cracked skins rendering the produce unmarketable in the fresh fruit industry.

Infection on young shoots results in stunted growth and the potential for twig dieback, which weakens the overall health of the tree.

Defoliation caused by early infection reduces the tree's photosynthetic capacity, affecting fruit size and next year's bud development.

Chronic infestations can lead to a general decline in tree vigor, making the orchard more susceptible to other stressors and winter injury.

Symptoms on fruit start as small, circular, dark green to olive-colored spots that eventually turn black and velvety as the fungus sporulates.

As the spots enlarge, the epidermis often cracks due to restricted tissue expansion, which may invite secondary decay-causing pathogens.

Twig lesions appear as small, slightly sunken, light-colored areas with a dark border, which later become sites of overwintering inoculum.

On leaves, the symptoms manifest as small spots that may drop out, creating a shot-hole appearance that can be confused with other diseases.

• Velvety fungal growth on spots
• Skin cracking and fruit deformity
• Sunken lesions on current-year twigs
• Premature leaf drop

Sanitation is key; pruning out infected twigs during dormancy significantly reduces the primary source of the fungal inoculum.

Improving orchard airflow through proper canopy management helps keep foliage and fruit dry, thereby discouraging spore germination.

Protective fungicide applications, particularly copper-based sprays, are effective during the early growth stages before the disease establishes.

During the growing season, systemic fungicides should be applied according to local scouting reports and weather forecasts indicating high infection risk.

Removing and destroying mummified fruit from the orchard floor is a critical step in managing the disease cycle for the following season.