Can plants get sunburned?

We all know that plants need light in order to grow, but too much sun can be harmful. When it comes to growing plants, six hours per day is considered full sun. In Alaska, our days receive a lot more than six hours of sunlight during growing season. With the rising temperatures, this can be a recipe for sun damage. Sunscald refers to damage on fruits and vegetables that is a result of high temperatures, intense solar radiation, or a combination of the two factors. This is similar to sunburn in humans. Sunscald typically affects the plant parts that we consume, such as the fruit. There are three different ways sunscald can affect plants: necrosis, browning, and photooxidative sunscald.

Necrosis sunscald affects many fruits and vegetables when temperatures exceed 100 degrees Fahrenheit. The resulting damage is the complete death of skin, peel, or fruit tissue where direct sun exposure has occurred. The injury may be white or brown in color and can appear as small to medium lesions. These lesions will be mushy. The fruit can still be consumed, however be cautious of any damage that has occurred from the lesions such as pest infestation, mold, or other fungus. Remove all affected areas before consumption.

Sunscald browning occurs at slightly lower temperatures and does not result in death of plant tissue, but rather slight damage and discoloration. The fruit or vegetable skin will have a yellow, bronze, or brown spot on the sun-exposed side. Unlike damage from sunscald necrosis, discolored areas caused by sunscald browning usually remain firm. Fruit with sunscald browning is more likely to be freshly consumed or used for canning, just remove the affected area first.

Photooxidative sunscald occurs when shaded fruit suddenly gets exposed to sunlight. This damage can occur at much lower temperatures and is typically a result of intense sudden light exposure. Photooxidative sunscald damage results in large areas of fruit that appear bleached and are completely white in color. These bleached areas will often appear sunken in, and outer tissue may be soft. It may wrinkle and develop secondary decay. Often these plants are too damaged to consume, lose their flavor, and rot very quickly. This sunscald also happens to plants that are not hardened off properly and then exposed to extreme periods of sunlight.

Sunscald damage could worsen in extreme weather, causing damage to spread and fruit to drop prematurely. Also, fruit with sunscald damage can become host to a secondary disease or infection. The best thing to do when you notice small amounts of sunscald damage is to remove the fruit. Immature fruit with damage can be composted or discarded. If the fruit is mature, cut out the damaged section and eat it promptly as sunscald will cause the fruit to rot quickly if left on the plant. To help prevent sunscald damage, the key is to keep the leaves and other parts of the plant healthy to help shade fruit. Adequate water is essential as well during extreme periods of heat, remember to water the soil and not the plant. Mulching is a great way to help retain moisture in your soil. If possible, providing temporary shade to your plants during extreme sun temperatures can also help prevent sunscald.