Plant sunburn, also known as sunscald or sun injury, occurs when plants are exposed to excessive sunlight, particularly during hot and dry conditions. While plants require sunlight for photosynthesis and growth, prolonged exposure to intense sunlight can damage their tissues, leading to various symptoms of sunburn. Sunburn is more common in young or tender plants, newly transplanted seedlings, and plants with thin or delicate foliage.

Symptoms:

1. Leaf wilting: Leaves may wilt or become limp due to the heat stress caused by intense sunlight. This wilting can occur even when soil moisture levels are adequate.
2. Leaf scorch: Sunburned leaves may develop brown or yellow scorched areas, particularly along the edges or tips of the leaves. The affected areas may become dry, crispy, and eventually die off.
3. Stem damage: Sunburn can also affect the stems of plants, causing them to become sunken, discolored, or cracked. The bark may peel off, exposing the underlying tissues to further damage.
4. Fruit damage: Fruits exposed to direct sunlight can develop sunburn symptoms, including discoloration, browning, and drying out. Sunburned fruits may become unsightly and may be more susceptible to rot and other diseases.

Causes:

Several factors can contribute to plant sunburn:

1. Intense sunlight: Plants exposed to prolonged periods of intense sunlight, particularly during the hottest part of the day, are more susceptible to sunburn. This is especially true for plants grown in open, sunny locations without adequate shade.
2. Thin foliage: Plants with thin or delicate foliage provide less protection against sunlight and are more prone to sunburn. This includes newly transplanted seedlings, young plants, and plants with sparse foliage.
3. Dry conditions: Hot and dry weather can exacerbate sunburn symptoms by increasing plant stress and reducing soil moisture levels. Plants under drought stress are more vulnerable to sunburn damage.

Recommendations and Preventive Measures:

1. Provide shade: Erect temporary shade structures or use shade cloth to provide protection for plants during the hottest part of the day, especially in regions with intense sunlight. Planting taller crops or installing trellises can also provide natural shade for smaller plants.
2. Water management: Maintain adequate soil moisture levels by watering plants regularly, especially during hot and dry weather. Use mulch to retain soil moisture and reduce evaporation.
3. Gradual acclimatization: Gradually acclimate young or tender plants to outdoor conditions by exposing them to increasing amounts of sunlight over a period of days or weeks. This allows plants to adjust to outdoor conditions without suffering from sunburn.
4. Avoid midday watering: Water plants early in the morning or late in the afternoon to avoid wet foliage during the hottest part of the day, which can increase the risk of sunburn.
5. Pruning: Prune dense foliage to improve air circulation and reduce the risk of sunburn. However, avoid excessive pruning, as this can increase sun exposure to sensitive plant tissues.
6. Protective barriers: Use reflective materials, such as white plastic or aluminum foil, to create barriers that reflect sunlight away from plants. This can be particularly effective for protecting young plants or seedlings.

By implementing these preventive measures and providing appropriate care, growers can minimize the risk of sunburn damage to their plants and promote healthy growth and development. Regular monitoring of plants for signs of stress and timely intervention are essential for preventing and mitigating sunburn damage.