Sun burns

• Symptoms :
  • Elongated and extensive necrotic lesions on the leaves.
  • Spots rather extensive on the face of the fruits most exposed to direct sunlight, irregular, whitish in their 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.

• 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 are exposed to solar radiation, in particular on their most exposed face. Such effects can occur more locally at the level of water droplets producing a magnifying effect, for example burning the limbus (figures 10 and 11).

• Diagnostic clues :
  • The phenomenon manifests itself during very sunny and hot climatic periods;
  • Affected plants are often distributed over the whole plot, in a dispersed manner;
  • Burns preferentially affect growing plants with tender leaf tissue, green fruits;
  • Only the parts of fruits and leaves most exposed to solar radiation are affected;
  • Deteriorated fruits are especially observed in the open field, the burnt leaves more under shelters;
  • Too much leaf stripping, pest attacks affecting the leaves may have preceded sunburn on fruit;

• Possible confusion  :

• Remedies : 
  • Avoid having plants that are too growing, with soft tissues, by managing fertilization as well as possible;
  • Shade cultures;
  • Control the pest (s) leading to a reduction in aerial vegetation.

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