The mango tree is a celebrated subtropical fruit producer, but its foliage is frequently subject to the appearance of dark spots. These black blemishes are a common source of concern for both commercial growers and home gardeners, signaling a disruption in the tree’s health. The presence of these spots suggests an underlying issue, ranging from a highly contagious pathogen to a simple environmental stressor. Correctly identifying the specific cause is the first step toward effective management and preserving the tree’s vigor and fruit yield.
Fungal Diseases Causing Black Spots
The most prevalent infectious cause of black spots on mango leaves is Anthracnose, a fungal disease caused by Colletotrichum gloeosporioides. This pathogen thrives in warm, highly humid conditions and spreads easily by wind and water splash, making it particularly active during rainy seasons or periods of heavy dew. On the leaves, the disease initially manifests as small, irregular dark spots that often enlarge and merge into necrotic patches.
These lesions are typically sunken and develop gray or tan centers with dark borders as they mature, often giving the foliage a scorched appearance. Anthracnose can infect all above-ground parts of the mango tree, including flowers and fruit. Infection of the blossoms, known as blossom blight, severely limits fruit set. Fruit infection often remains latent until the fruit begins to ripen post-harvest.
Treating Anthracnose involves a combination of cultural and chemical controls to reduce the fungal load. Pruning out and destroying all infected plant material, such as dead twigs and mummified fruit, minimizes the source of spores. Chemical management relies on the timely application of fungicides. Copper-based sprays or broad-spectrum fungicides like Mancozeb or Azoxystrobin are effective when applied protectively during new flushes and flowering stages. Maintaining a protective fungicide coating is important during periods of high moisture.
Bacterial Black Spot and Canker
Another cause of dark spots is Bacterial Black Spot (BBS), a disease caused by the bacterium Xanthomonas axonopodis pv. mangiferaeindicae. This bacterial infection presents symptoms that can be confused with Anthracnose, but the spots have distinct characteristics aiding in proper diagnosis. Bacterial leaf lesions are often angular because they are restricted by the leaf veins, giving them a sharp, geometric boundary.
These spots are initially water-soaked, then turn black and develop a raised, corky, or cracked texture, which is a hallmark of a canker. A bright yellow halo frequently surrounds the raised black spots, especially on younger leaves. The bacteria spread rapidly via wind-driven rain and enter the plant through natural openings or small wounds. Damage from high winds provides easy entry points.
Standard fungicides are ineffective against this bacterial pathogen. Management relies on using bactericidal treatments, primarily copper compounds, applied preventatively from panicle emergence through harvest. Strict sanitation is paramount, including sterilizing pruning tools with a bleach solution after trimming each tree to prevent mechanical spread. Avoiding overhead irrigation is also a recommended cultural practice, as it significantly reduces the water splash that facilitates bacterial dispersal.
Non-Pathogen Related Causes
Not all black spots on mango leaves result from an infectious pathogen; some are environmental or nutritional issues. Environmental stresses, such as cold temperatures, can cause necrotic spots that appear dark or black on the leaf tissue. Similarly, excessive sun exposure, particularly on new leaf flushes, can lead to localized cell death that mimics disease lesions.
Nutrient deficiencies can also manifest as dark spotting or discoloration. A lack of micronutrients like zinc or manganese can disrupt normal leaf development, causing patterns of dark, dead tissue. If the spots follow a predictable pattern across a new leaf flush without the raised or sunken characteristics of major diseases, a soil test may be warranted to correct nutritional imbalance.
Dark spots can also result from secondary issues like Sooty Mold. This mold is a fungus that grows superficially on honeydew, the sugary excrement left by sap-sucking insects like scale, mealybugs, or aphids. The mold does not infect the leaf tissue but forms a thick, black coating that blocks sunlight, impeding photosynthesis. Treating this involves controlling the underlying insect pest population, often with horticultural oils, which eliminates the honeydew source and allows the mold to dry and flake off.
Integrated Management and Prevention
A sustainable strategy for controlling black spots involves Integrated Pest Management (IPM), combining cultural, physical, and chemical controls. Long-term health begins with selecting a planting site that provides good sunlight and air movement, ensuring foliage dries quickly after rain or dew. Proper tree spacing and annual pruning to open the canopy are necessary to maximize air circulation.
Sanitation involves promptly removing and destroying all fallen leaves, fruit, and pruned wood, as this debris harbors fungal spores and bacteria. Protect the tree from mechanical injury, as wounds serve as entry points for pathogens, especially the bacteria that cause BBS. This includes establishing windbreaks to minimize wind-related abrasions on leaves and fruit.
Water management is an effective preventative measure; switching from overhead sprinklers to drip or micro-sprinkler irrigation keeps the foliage dry, reducing disease spread. When chemical control is necessary, it must be targeted and timed to protect new growth flushes and flowering periods. Combining these cultural practices with specific chemical applications substantially reduces the incidence of black spot diseases and maintains a productive, healthy mango tree.