Dark spots on apple leaves in late summer may signal a fungal threat

Dark spots appearing on apple tree leaves and fruits in late summer are often mistaken for natural aging. However, these signs typically indicate a fungal infection—specifically apple scab—which can rapidly transform a healthy harvest into shriveled, unusable fruit within a few weeks. Identifying Apple Scab and Plausible Causes The primary observed sign is the appearance of dark spots on both the foliage and the fruit. While these may resemble physiological aging or nutrient deficiencies, their progression across the canopy and onto the ripening apples suggests a fungal pathogen. In wet weather, spores are carried by wind and water, allowing the infection to spread to neighboring trees within days. Observed Sign/Action Result/Indication Black spots on fruits Active phase of apple scab Bordeaux mixture (1%) Elimination of the fungus Removing fallen leaves Reduced risk of spring infection Mustard spray Safe harvest prophylaxis Chemical Control: Copper-Based Protection Bordeaux mixture remains a reliable method to halt fungal spread. For August applications, a 1% concentration is recommended to avoid damaging the plant. The application should be carried out in dry weather during hours of low solar activity; spraying at midday can lead to foliage burns.