Peach scab

Taxonomic position and pathogen type: Fusicladium carpophilum (also known as Venturia carpophila) is an ascomycete fungus that acts as a significant plant pathogen. It is classified within the family Venturiaceae. As a biotrophic or hemibiotrophic parasite, it specializes in attacking stone fruit crops, causing the disease commonly referred to as peach scab.

Diseases and host crops: This pathogen primarily infects peach, nectarine, apricot, and almond trees. The disease affects the fruit, leaves, and young twigs. Symptoms appear as small, circular, dark green to black spots on the skin of the fruit. In severe cases, these lesions coalesce, causing the fruit to crack and deform, making it unsuitable for commercial sale. Twig infections manifest as small, brown lesions which can girdle the shoot.

Biology and life cycle: The fungus overwinters as mycelium in the lesions of infected twigs and on mummified fruits remaining in the tree or on the orchard floor. In the spring, when temperatures rise and humidity levels increase, conidia are produced. These spores are disseminated by wind and rain splashes to new, developing tissues. Once the infection is established, the fungus produces secondary spores throughout the growing season.

Conditions for development and economic impact: The development of Fusicladium carpophilum is heavily dependent on moisture. High humidity (over 85%) and frequent rainfall are critical for spore germination and infection. Temperatures between 18°C and 24°C are optimal for rapid disease progress. Economic damage is substantial, as it leads to high percentages of unsaleable fruit, increased costs for chemical inputs, and overall weakening of the orchard health.

Protection and control measures: Managing peach scab requires an integrated approach to minimize the primary and secondary inoculum sources:

• Removal and destruction of infected twigs and mummified fruit during dormant pruning.
• Ensuring good orchard sanitation by removing plant debris that harbors the pathogen.
• Pruning for better canopy light penetration and air circulation to reduce humidity.
• Applying preventive and curative fungicide sprays during critical infection windows, such as the period from petal fall to fruit maturity.