A previously undescribed viras disease of lettuce, sugarbeets, other crop and weed hosts was found in the southwest desert regions of U.S.A. Affected lettuce and sugarbeet hosts exhibited interveinal yellowing, stunting, rolling, and brittleness of affected leaves. Since 1990, yellowing symptoms on desert lettuce and sugarbeet were shown to be induced by a mixture of lettuce infectious yellows viras (LIYV) and this previously undescribed viras termed lettuce chlorosis viras (LCV). LCV is a closterovirus with flexuous, filamentous particles 800–850 nm long. The viras is transmitted efficiently by bothBemisia biotypes. LCV differs significantly from LIYV and other previously described viruses in host range (LCV does not infect the Cucurbitaceae), insect transmission, and serology.