Brown spots on mangoes, appearing on fruit, leaves, and stems, are caused by diseases, environmental stressors, and physiological issues.
Identifying Brown Spots on Mangoes
Brown spots vary in appearance, location, size, shape, and texture, offering clues about their origin. Small, dark, angular spots on leaves, often restricted by veins and potentially surrounded by a yellow halo, may indicate bacterial infection. These lesions can coalesce into larger dead patches, turning gray and cracking.
Fungal infections present differently. On leaves, spots may start as small, angular brown to black areas that enlarge. On fruit, fungal spots, like anthracnose, typically appear as irregular, dark brown to black, sunken lesions that can coalesce and penetrate deep into the flesh. Chilling injury causes grayish, scald-like skin discoloration, pitting, uneven ripening, and possible internal browning. Sunburn on fruit results in dry, shrunken, tan to brown areas, often with darker edges.
Common Causes of Brown Spots on Mangoes
Brown spots stem from pathogens, nutrient imbalances, and environmental conditions.
Fungal Diseases
Anthracnose, caused by Colletotrichum gloeosporioides, is a common fungal disease. It leads to dark brown to black spots on leaves, stems, flowers, and fruit. On young leaves, spots may be small and angular, expanding into larger, dry patches, sometimes causing defoliation. On fruit, lesions are typically sunken, dark brown to black, leading to extensive rotting as the fruit ripens. Powdery mildew is another fungal issue, characterized by white, powdery growth on leaves, flowers, and young fruits, which can later turn purplish-brown.
Bacterial Diseases
Bacterial black spot, caused by Xanthomonas campestris pv. mangiferaeindicae, manifests as raised, black, angular spots on leaves, often with greasy margins. On fruit, lesions begin as small, water-soaked specks that blacken, develop raised margins, and may crack. Unlike anthracnose, these lesions do not expand as the fruit ripens.
Nutrient Deficiencies
Micronutrient deficiencies can cause browning. Boron deficiency leads to fruit cracking and brown areas within the pulp. Calcium deficiency may result in darkened leaf margins, which can later yellow and fall off, and contribute to cellular tissue degeneration within the fruit.
Environmental Stress
Sunburn causes dry, shrunken, tan to brown areas on fruit exposed to intense sunlight, especially in high temperatures or with surface moisture. Cold damage can lead to browning or blackening of leaves and twigs, and dieback. Water stress, from too much or too little water, can also contribute to discoloration and plant decline.
Physiological Disorders
Chilling injury occurs when mangoes are stored below approximately 12.5°C (55°F). Symptoms include grayish or brown skin discoloration, pitting, uneven ripening, and internal browning of the pulp, often appearing after fruit is moved to warmer temperatures. Internal flesh breakdown, seen as dark brown discoloration near the seed, can be associated with long storage or suboptimal conditions.
Preventing Brown Spots on Mangoes
Proactive measures and sound cultural practices minimize brown spots and foster tree health.
Proper site selection and planting are foundational. Mango trees thrive in well-drained soil and ample sunlight. Adequate drainage prevents waterlogging, which can predispose trees to disease.
Good sanitation practices are important. Regularly removing diseased plant material, such as fallen leaves and infected branches, reduces pathogen sources and minimizes fungal and bacterial spore spread.
Appropriate watering techniques prevent drought stress and excessive moisture. Consistent, deep watering is preferred over frequent, shallow irrigation, which can encourage superficial root growth and fungal development. Balanced nutrition also prevents deficiencies that can manifest as brown spots or increase disease susceptibility.
Strategic pruning improves air circulation within the tree canopy. Removing dense foliage allows better airflow, reducing humidity around leaves and fruit, creating an environment less favorable for fungal and bacterial growth. Selecting disease-resistant mango varieties, such as those resistant to anthracnose or bacterial black spot, is also a preventive strategy.
Managing Existing Brown Spots on Mangoes
Once brown spots appear, prompt and targeted management can mitigate their impact and prevent further spread.
Pruning affected parts is a primary step. Carefully remove and dispose of diseased leaves, branches, or fruit to reduce pathogen presence. Sterilizing pruning tools between cuts with a disinfectant, such as bleach, prevents disease transfer to healthy sections.
For identified fungal or bacterial issues, applying appropriate fungicides or bactericides is often necessary. Copper-based fungicides are commonly used for anthracnose and bacterial black spot, applied according to product instructions, often from flowering until harvest. Newer fungicides, such as strobilurin fungicides like azoxystrobin, can also be integrated into spray schedules for anthracnose control.
Adjusting environmental conditions can aid recovery. Protecting trees from freezing temperatures prevents further cold damage. For sunburn, providing temporary shade to developing fruit reduces direct sun exposure. Modifying irrigation schedules to ensure optimal soil moisture supports overall plant health and recovery.
When nutrient deficiencies are the cause, correcting the imbalance is necessary. This may involve applying foliar sprays or soil amendments containing the deficient nutrient, such as boron or calcium. Soil testing can confirm specific nutrient needs, allowing for precise nutrient correction.