It is usually due to fungi or oomycetes, such as the potato blight (Phytophthora infestams), or occasionally to bacterial infections, as in fireblight of pears, which is caused by Erwinia amylovora.

• 通常是由真菌和卵菌引起的，例如感染马铃薯的马铃薯晚疫病菌（疫霉属Phytophthorainfestams），枯萎病偶尔也可由细菌感染，如导致梨火疫病的解淀粉欧文氏菌Erwiniaamylovora。