Blight refers to way plants wither when infected. It is usually caused by fungi, or viruses, or sometimes by bacteria.

Blight is a rapid and complete chlorosis,^[1] browning, then death of plant tissues such as leaves, branches, twigs, or flowers.^[2] Various diseases which cause the symptom are known as blights. Several notable examples are:

• Late blight of potato, caused by the water mould Phytophthora infestans, the disease which led to the Irish potato famine
• Southern corn leaf blight, caused by the fungus Cochliobolus heterostrophus. This caused a severe loss of corn in the United States in 1970.^[3]
• Chestnut blight, caused by the fungus Cryphonectria parasitica has nearly eradicated mature American chestnuts in North America.
• Bacterial leaf blight of rice is caused by the bacterium Xanthomonas oryzae.^[4]
• Early blight of potato and tomato, caused by species of the common fungal genus Alternaria.
• Leaf blight of grasses. On leaf tissue, symptoms of blight are the initial appearance of lesions which rapidly engulf surrounding tissue.