Sunburn damage on fruit can be a serious issue, especially when the fruit is exposed to intense sunlight. Affected areas often show light brown, round spots on the surface, with unclear edges. Initially, the fruit skin may shrink and then gradually sink, eventually leading to dry, shriveled fruit in severe cases. Young shoots and tender growth are also vulnerable; sunburn can cause tip dieback or leaf wilting.
The disease typically occurs between mid-June and early July, during the fruit coloring and ripening stage. It mainly affects fruits that are directly exposed to the sun. The primary cause is water stress—when the tree lacks sufficient moisture, and the fruit cannot absorb enough water. If root absorption is limited but transpiration from the leaves is high, it creates an imbalance in the fruit’s water content, leading to sunburn. Root damage or root burning can also contribute to this condition. Large-fruited varieties are particularly prone to sunburn.
In some cases, sunspots may appear on fruits and shoots due to movement caused by pruning, topping, or vine training. Sudden temperature increases can also trigger similar symptoms.
To manage sunburn, proper orchard management is essential. Deep fertilization should be applied appropriately to encourage deeper root development, which helps improve tree vigor and resilience. Planting at suitable densities and using trellis systems can help keep fruit clusters in shaded areas. Avoid overwatering or excessive fertilization, as these can lead to weak root systems. During hot periods, timely and adequate irrigation is crucial to reduce plant temperatures and prevent sunburn.
Additionally, foliar sprays can be effective. After rainy weather, applying 0.2% potassium dihydrogen phosphate, 5% wood ash solution, or 27% high-fat film emulsion diluted 80–100 times to the leaves and fruit clusters 2–3 times can help reduce the risk of sunburn. These measures provide a protective effect and support the plant’s natural defenses against heat stress.
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