Symptoms and Signs
Early symptoms of turnip mosaic include numerous small, light green, circular and irregular lesions on leaves. Later symptoms include veinal chlorosis, curvature of the midrib, asymmetrical distortion of the leaf blade, and necrosis of lower leaves. Lettuce infected early may be severely stunted, and can result in unmarketable heads.
Comments on the Disease
Turnip mosaic virus (TuMV) is not a common disease of lettuce. Other hosts, such as escarole and endive, are likewise rarely infected in California. However, the virus has a wide host range. It is found in 20 plant families and is especially common in crucifers.
Turnip mosaic virus is transmitted in a nonpersistent manner by many species of aphids. The virus is not seed transmitted.
Management
Grow resistant crisphead lettuce varieties. Butterhead, leaf, or romaine lettuce types are all resistant.