Diseases of Lettuce

A member of the Asteraceae, lettuce (Lactuca sativa L.) is one of the most popular salad crops in the world. Its broad adaptability and wide distribution make it subject to numerous fungal, bacterial, viral, and nematode-causing diseases. Downy mildew, bottom rot caused by Rhizoctonia solani, and lettuce drop caused by Sclerotinia spp. all rank as important diseases wherever lettuce is grown, while a number of additional fungal disorders are more regionally significant. These include anthracnose, Cercospora leaf spot, Fusarium wilt, powdery mildew, southern blight, and Verticillium wilt. Of lettuce bacterial diseases, bacterial leaf spot, soft rot, and varnish spot occasionally cause significant losses when not controlled. Lettuce mosaic, lettuce big-vein, impatiens necrotic spot, and tomato spotted wilt are all important viral diseases of lettuce, while the ubiquitous root-knot nematode is the most prominent nematode pest. Asters yellows and tipburn, a phytoplasmal disease and an abiotic disorder, respectively, round out a list of the most significant diseases. Managing these diseases and disorder is required for successful lettuce production. Disease management strategies vary for each, but typically include cultural, biological, chemical, regulatory strategies, and genetic resistance.