此种疾病通常由细菌或真菌引起，例如土豆的疮痂（由疥疮链霉菌引起），和苹果黑星病（由不等黑星菌引起）。

• The disease is usually caused by a bacterium, e.g. common scab of potatoes (Streptomyces scabies), or a fungus, e.g. apple scab (Venturia inaequalis).