Lettuce Diseases and their Management

Abstract

Lettuce is the world's most popular leafy salad vegetable. Various types of lettuce are cultivated across the globe, primarily for human consumption of their fresh, succulent leaves. Over 75 lettuce disorders of diverse causes and etiologies have been described. While some diseases are limited in their importance and distribution, a significant number are present wherever Lactuca sativa L. is grown. Many are capable of causing devastating losses in yield and quality under favorable conditions. In this chapter, we have divided lettuce diseases broadly into infectious and non-infectious disorders. Of the important infectious diseases covered, fungi and viruses account for the bulk. Nine fungal diseases are discussed, including anthracnose, bottom rot, Cercospora leaf spot, damping-off, downy mildew, drop, gray mold, Septoria leaf spot, and southern blight. Five viral diseases are covered, and these are: beet western yellows, lettuce big-vein, lettuce infectious yellows, lettuce mosaic, and tomato spotted wilt. The sole phytoplasmic lettuce disease, aster yellows, is also discussed. Of five important bacterial diseases detailed, four are foliar disorders: bacterial leaf spot, marginal leaf blight, soft rot, and varnish spot. Corky root is the one bacterial root disease included. In contrast, all nematode pathogens discussed, lesion, needle, and root-knot nematodes, infect lettuce roots. Three important non-infectious disorders are included in this chapter, namely brown stain, pink rib, and tipburn. These are mainly disorders of mature or postharvest lettuce.