Sunburn is damage to foliage and other herbaceous plant parts caused by a combination of too much light and heat and insufficient moisture. A yellow or brown area develops on foliage, which then dies beginning in areas between the veins.
Avoid sunburn by providing shade and proper cultural care, especially adequate irrigation. Appropriate irrigation before discolored leaf tissue is killed can usually restore the green color to sunburned foliage.
Sunburn damage to impatiens leaf
Necrotic sunburned leaf tip of hydrangea