In recent years lettuce dieback has appeared in some romaine plantings in southeastern Imperial County, California and in Yuma, Arizona. The disease is caused by the lettuce necrotic stunt virus. Initial symptoms on infected plants consist of extensive yellowing of the outermost leaves, with the younger inner leaves usually remaining dark green in color. Dead spots on older leaves can develop into extensive areas of brown necrotic tissue. As the disease progresses, plant stunting and death can occur. Rotted roots may also be present, but whether this is caused by the virus or is a secondary issue is not clear. Lettuce dieback is primarily a disease problem on romaine lettuce, although some green leaf, red leaf and butterhead cultivars can be affected as well. To date, symptoms have not been observed on commercial iceberg lettuce. The lettuce necrotic stunt virus is unusual in that no vector is known for this pathogen. Lettuce dieback is associated with fields near rivers. The virus can be dispersed by contaminated soil and water, where it can survive for a long period of time. The most effective management strategy for lettuce dieback is to plant iceberg lettuce and avoid planting romaine or susceptible cultivars of other types of lettuce. Fumigation of soil with methyl bromide and chloropicrin does not reduce the incidence of disease.

For questions or comments on any of the topics please contact Marco Pena at the Yuma Agricultural Center.
College of Agriculture, The University of Arizona, Tucson, AZ.