- Citrus

Citrus Citrus



Abiotic Sunburn

In a Nutshell

  • Wilting and yellowing of leaves, starting from the margins.
  • Fruit and bark also affected after defoliation.
 - Citrus

Citrus Citrus


Abiotic sunburn refers to the damage caused to plants, bushes or trees by a combination of direct sunlight and excessive temperatures. These factors alter the moisture in the plant tissues, leading initially to the wilting of young, tender leaves. These leaves gradually turn pale green and start to develop lesions near the apex and the margins after 2–3 days. The parched lesions later progress towards the middle of the leaf lamina. The defoliation caused by drought stress or insect attack can also lead to sunscalds to fruit or bark, since these are not shaded by the leaves anymore. In the bark they can take the form of cracks and cankers, which eventually develop into dead areas on the trunk.

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Sunburn injury is common in plants or trees grown in areas with high solar radiation, high air temperatures, and low relative humidity. Altitude also plays a role since the ultraviolet (UV) radiation is greater at higher elevations. Symptoms are visible on leaves, fruits and bark. The incidence and severity of sunburn also depends on factors such as the variety of plant, its growth stage and soil moisture. Sunburn is particularly severe when air temperature and the number of sunny hours are high during the ripening period. The alternation of weather events is also important: thus, damage can also occur when cool or mild weather is abruptly followed by hot, sunny weather.

Organic Control

White clay or talc formulations can be sprayed on foliage and trunk to physically block the sunlight. This may reduce temperatures by 5-10 °C. Products based on calcium carbonate or crystalline limestone are also recommended. Carnauba wax products serve as a natural sunscreen to plants.

Chemical Control

Always consider an integrated approach with preventive measures together with biological treatments if available. Abscisic acid applied as a fertilizer supplement helps to reduce sunburn damage to fruits such as apples and may therefore also work in other crops. Anti-transpirant products that reduce water loss by the leaves, such as those based on poly-1-P menthene, have also shown good results in some studies.

Preventive Measures

  • Use varieties that are more tolerant to sunburn.
  • Make sure that the irrigation is well-matched with the crop's water requirements.
  • Irrigate just before heat waves to avoid plant stress and sunburn.
  • Avoid excessive summer pruning and leaf stripping.
  • Improve air movement through the canopy.
  • Implement a plant or tree sprinkler cooling system.
  • Shade netting or fruit bagging can also be applied if needed.
  • Use cover crops between the rows to enhance soil water retention capacity (maize or pigeon pea in pineapple orchard for example).

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