Sunburn

 (sunscald)

• Symptoms :
  • rather extensive spots on the side of the fruits most exposed to direct sunlight, irregular, whitish in the center, and more or less surrounded by a yellow halo. They are slightly depressed, and their surface is more or less wrinkled and takes on a dry texture reminiscent of paper.
  • elongated and extensive necrotic lesions on the leaves

• Cause(s) : the fruits of certain vegetable species (figures 1 to 8), the young leaves (figures 9 to 11) are rather delicate organs whose tender and waterlogged tissues sometimes dehydrate locally and superficially when they are exposed to solar radiation, especially on their most exposed face. Such effects can occur more locally at the level of water droplets producing a magnifying effect burning the limbus, for example (FIGS. 10 and 11).

• Diagnostic clues :
  • the phenomenon occurs during very sunny and hot climatic periods;
  • the plants affected are often distributed over the whole of the plot, in a dispersed way;
  • burns preferentially affect growing plants with tender leaf tissue, green fruits;
  • only the parts of the fruits and leaves most exposed to solar radiation are affected;
  • damaged fruits are mainly observed in the open field, the burnt leaves more under shelter;
  • too much leaf stripping, attacks by pests affecting the leaves may have preceded sunburn on the fruits;

• Possible confusion :

• Remedies : 
  • avoid having plants that grow too much, with soft tissues, by managing fertilization as well as possible ;
  • shade crops;
  • controlling the pest(s) causing a reduction in aerial vegetation.

• Note : note that these superficial lesions, particularly on fruits, can be invaded by various secondary saprophytic fungi, sometimes causing rot.