If you happen to find a pale blister-like patch on a fruit or vegetable, don’t assume that it’s damage caused by a disease or an insect pest. Your plant may be suffering from sunscald — a sudden exposure to bright sunlight. Once the fruit or vegetable is damaged, it’s an entryway for insects, fungi, and bacteria. Sunscald is especially common in grapes, peppers, apples, raspberries and tomatoes, and also in some trees, and usually occurs during hot sun or when conditions warm suddenly while the ground is still frozen, so that a plant’s roots can’t take in water.
The affected areas on fruits may resemble water-filled blisters, which eventually dry up and become sunken and brown along the edges. Sometimes, the blisters are surrounded by a grayish-white margin. Minor cases of sunscald can also result in leaf loss or, in extreme cases, withering and death of a plant’s stems. In trees, sunscald causes cracking and splitting of the bark, which can result in infection.
How to Avoid Sunscald
To avoid sunscald in young plants, be sure to harden off your seedlings for about a week before planting them and exposing them to a full day of bright sunlight. Fruiting crops, especially grapes, can be covered with a shade cloth for at least part of the day. Keep plants healthy with plenty of foliage to protect fruits and vegetables. To preserve trees from sunscald’s effects, paint their trunks with white latex paint, or wrap them in a light-reflective covering.
How To Identify Sunscald: Images
Not sure if you’ve got sunscald in the garden? Here are some great resource websites with images of sunscald on leaves, fruit, vegetables and tree trunks!
Sunscald of Tomato and Peppers Images from Missouri Botanical Garden.
Sunscald Images from Washington State University.
Hot and Sunny Days Promote Sunscald in Peppers and Other Vegetables Images from Michigan State University Extension.