Many viruses are difficult to distinguish from one another by symptom alone. In addition, for each particular disease, the symptoms will vary greatly depending on stage of plant at time of infection and other factors. In general, symptoms consist of various leaf and plant deformities, stunting and poor growth, and yellowing or a mosaic or mottling pattern in the leaves. Identification of the particular pathogenic agent can only be made with serological, inoculation, or other laboratory tests.
Life cycle
For the most part, beet western yellows (BWYV), cucumber mosaic virus (CMV), curly top virus, lettuce mosaic, and lettuce infectious yellows (LIY) occur sporadically. All of these pathogens have numerous alternate crop and weed hosts. These pathogens are spread by insect vectors that have fed on the sap of infected plants (aphids, primarily green peach aphids, for beet western yellows virus, cucumber mosaic virus, and lettuce mosaic; whiteflies for lettuce infectious yellows virus; and the beet leafhopper for curly top virus).
Solutions
Buy and plant virus-free seed if available. Resistant varieties may be available. After symptoms on plants occur, there is no practical control. Reflective mulches or row covers may help prevent infection by aphid- and leafhopper-transmitted viruses. Plants showing symptoms near harvest are edible. Plants that show symptoms early may be small or may not form heads.
