Apricots are a prized stone fruit, but brown spots on the skin are a common problem for growers. These discolorations signal an underlying issue, often the presence of a pathogen or a response to environmental stress. The causes fall into distinct categories: fungal infections, bacterial diseases, and non-infectious physiological disorders. Understanding the visual differences between these causes is the first step toward effective management.
Primary Fungal Causes
The most frequent causes of brown spots on apricots are fungal pathogens, particularly those responsible for Brown Rot. This disease is caused by the fungus Monilinia fructicola, which targets the fruit as it ripens, though it also affects blossoms and twigs earlier in the season. The infection starts as a small, circular, soft brown spot that rapidly expands to consume the entire apricot, often in as little as two days under warm, humid conditions. A characteristic sign is the development of fuzzy, buff-to-gray-colored spore masses covering the rotting area. Infected fruit shrivels into a hard, wrinkled “mummy” that serves as a primary source of infection for the following year.
A second fungal issue is Apricot Scab, caused by the fungus Cladosporium carpophilum, which results in a more superficial spotting. This pathogen thrives in wet weather and shaded conditions, with lesions typically appearing six to seven weeks after the blossoms fall. The resulting spots are small, round, and olive-green to dark brown, often clustered near the stem end.
Unlike the soft rot of Brown Rot, these lesions are shallow and slightly raised, often described as “freckles.” They may merge to form larger, scabby blotches. In severe cases, the affected skin may crack, allowing secondary fungi to invade the fruit and cause deep decay.
Non-Fungal and Environmental Triggers
Brown spots not caused by fungal pathogens often result from bacterial infection or physical environmental damage. Bacterial Canker, caused by Pseudomonas syringae, presents different symptoms on the fruit. The spots on the apricot skin are initially water-soaked before turning dark brown or black and becoming sunken. This bacterial issue is distinguished by the presence of amber-colored gum, known as gummosis, exuding from cankers on the twigs and branches.
Environmental factors can also create non-infectious brown spots, such as Sunscald, a physiological disorder. This damage occurs when fruit is suddenly exposed to intense sunlight and heat, often after protective leaves are removed by disease or improper pruning. The side of the fruit facing the sun develops a discolored patch that appears yellow-white or leathery and dry, eventually turning brown.
This is a form of physical damage, and while the affected tissue is non-infectious, it may be colonized by secondary molds. Other physiological spotting can stem from water stress or nutrient imbalances, leading to surface discoloration or cracking.
Diagnosis and Management Strategies
Properly identifying the cause of the brown spots is the first step in effective management, as treatments for fungal, bacterial, and environmental issues differ. A simple diagnostic checklist helps differentiate the causes. The presence of fuzzy, gray-brown spore masses indicates Brown Rot, while clear or amber-colored sap oozing from the twig is typical of a bacterial or canker issue. Sunscald spots are easy to identify because they occur only on the side of the fruit facing the strongest afternoon sun and lack any fungal growth or deep-seated rot.
General management relies heavily on cultural control, focusing on preventative and non-chemical actions. Sanitation is critical and requires removing all infected fruit, including the dried “mummies” that remain on the tree or on the ground, as these harbor overwintering spores.
Pruning is an effective tool, as it improves air circulation and sunlight penetration throughout the canopy, reducing the moist conditions that favor fungal growth. Avoiding overhead watering helps minimize the dispersal of fungal and bacterial spores, which are often spread by splashing water.
Maintaining tree vigor through proper nutrition and irrigation also reduces susceptibility to bacterial canker, since the pathogen Pseudomonas syringae targets weakened trees.