Sunscald
Class: Environmental Damage
Common Name
Sunscald
In Short
Sunscald refers to a condition that occurs when plants are exposed to intense heat stress such as direct sunlight. Some plant species are more susceptible than others, but broadly speaking, the most affected parts are the leaves, stems, bark, and fruits.
Triggers
Pre-planned defoliation from pruning can cause a sudden exposure to direct sunlight.
Changes in weather conditions, such as a rapid transition from winter-like conditions to a spring-like conditions that more resemble summertime than springtime.
Symptoms
On fruits: Sunscald occurs on the sides exposed to direct sunlight and leads to a sudden rise of fruits’ internal temperature which causes tissue damage. It first appears as a wrinkled area that can be soft and lighter in color than surrounding tissue. This area later turns white and paper-like. The affected area often turns black due to the colonization of fungi that live on dead tissue. Fruit near maturity are more sensitive to sunscald injury than immature fruits.
In vegetables, symptoms are similar in appearance to those of blossom-end rot, but they appear on the surfaces exposed to direct sunlight. In citrus crops, symptoms are similar in appearance to those of rust mites.
On bark: Citrus, mango, avocado, lychee, nectarine, apples, fig, and many more are considered susceptible. Their bark, branches, and stems are easily injured and die from exposure to direct intense sunlight. Symptoms usually include cracking of bark, splitting of the stem, and burned and scorched like branches.
On leaves: Unusually large areas of light to white colored pigment appear and sometimes scorched and dried leaves.
Control measures
Prevention
Reduce the intensity of sunlight reaching your plants. When summer-like conditions are expected, encourage abundant, healthy foliage with proper fertilization and irrigation.
Open fields
In vegetables and field crops: If feasible, cover your crops with dedicated shading nets that significantly reduce the amount of direct sunlight on them. You can do this by constructing a relatively cheap frame made from small metal arcs that act as a miniature net house.
In greenhouses and other structures covered with polyethylene: Shade plants during the summer by introducing dedicated shading nets and deploying them on polyethylene sheets on the roof.
In the orchard: Plan ahead, before summer-like weather conditions are present. Tree stems should be painted with a specially designated white paint or wrapped with a designated material in order to reduce the intensity of the direct sunlight.
Caution and careful notice should be taken when using any plant protection products (insecticides, fungicides, and herbicides). It is the grower’s sole responsibility to keep track of the legal uses and permissions with respect to the laws in their country and destination markets. Always read the instructions written on labels, and in a case of contradiction, work in accordance to the product label. Keep in mind that information written on the label usually applies to local markets. Pest control products intended for organic farming are generally considered to be less effective in comparison to conventional products. When dealing with organic, biologic, and to some extent a small number of conventional chemical products, a complete eradication of a pest or disease will often require several iterations of a specific treatment or combination of treatments.