Mango trees, like many plants, are susceptible to damage from excessive solar radiation, a condition commonly referred to as sunburn. This physiological disorder occurs when the intensity of sunlight, often combined with high temperatures, overwhelms the plant’s natural protective mechanisms. Sunburn on mangoes manifests as direct tissue damage, which can affect the leaves, bark, and most notably, the developing fruit.
Identifying Mango Sunburn
Sunburn presents distinct visual cues on different parts of the mango tree. On the fruit, sunburn typically appears as dry, shrunken, tan to brown patches, usually on the side most exposed to the sun. These discolored areas often have darker edges, and the affected flesh underneath can become leathery, reducing the fruit’s palatability and making it suitable primarily for juice. This damage can sometimes resemble a “lens effect,” where moisture on the fruit’s surface magnifies the sun’s heat, effectively cooking the tissue.
Mango leaves, when affected by severe sun exposure, may exhibit signs of stress such as yellowing and eventual drying out, which can reduce the overall protective canopy. The bark of mango trees, particularly on younger specimens or exposed branches, can also suffer sunburn. This damage often appears as dark, discolored patches that may lead to cracking and peeling. On young trees, a brown, slightly sunken canker, typically 5-8 cm in length, can develop on the trunk just above ground level.
Factors Increasing Sunburn Risk
Several environmental conditions and plant characteristics can significantly increase a mango tree’s susceptibility to sunburn. Prolonged periods of high temperatures, especially those exceeding 38 degrees Celsius (100 degrees Fahrenheit), create an environment where sunburn is more likely. The combination of intense sunlight with high heat and moisture on plant surfaces can intensify damage.
Trees that experience sudden exposure to intense sunlight are particularly vulnerable. This often happens after significant pruning, which removes the protective leaf canopy, or when newly planted or transplanted trees are introduced to full sun without proper acclimatization. Young or recently established trees are more susceptible than mature, well-established ones. Drought stress or insufficient watering further compromises a tree’s ability to cope with heat, making it more prone to sunburn. Additionally, reflective surfaces nearby, such as concrete or light-colored walls, can intensify sun exposure, increasing the risk of sunburn.
Preventing and Managing Mango Sunburn
Protecting mango trees from sunburn involves a combination of preventive strategies and supportive care. Providing shade is one effective method, achieved by using shade cloth during peak sun hours or by strategically planting trees in an east-west direction to minimize direct afternoon sun exposure. Another protective measure involves applying a diluted white latex paint to trunks and exposed branches, especially after heavy pruning or transplanting. This reflective coating helps deflect sunlight and reduce heat absorption.
Ensuring adequate and consistent watering is also important, particularly during hot, dry periods or before anticipated heat waves. Proper hydration helps the tree manage heat stress more effectively. For newly planted or relocated trees, gradual acclimatization to full sun conditions can prevent shock and sunburn. Careful pruning practices are essential; avoid excessive removal of foliage, especially during hot months, to maintain a dense canopy that naturally shades the fruit and bark. Selecting mango cultivars known for good foliage cover can also reduce sunburn risk.
If sunburn damage has already occurred, supportive care can help the tree recover. Severely damaged fruit will likely have reduced quality and can be used for juice. For bark damage on trunks, new shoots may emerge below the affected area, which can be trained to regenerate the tree. Chemical sprays like kaolin or magnesium carbonate can reflect radiation and reduce temperatures on leaves and fruit, applied preventatively. Bagging individual fruits with specialized bags can also offer protection from direct sun exposure and improve fruit quality.