Spinach was demonstrated to be naturally infected in California with sugarbeet mosaic and two cucumber mosaics-western cucumber mosaic and celery calico. Nine varieties of spinach were experimentally infected with the two cucumbermosaic viruses, five with sugar-beet mosaic. The three viruses were recovered from naturally infected spinach and transferred by mechanical inoculation to White Spine cucumber (Cucumis sativus) , Turkish tobacco (Nicotiana tabacum), N. glutinosa, or sugar beet (Beta

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... garis). The symptoms of these three diseases on spinach are similar. Filamentous leaves occur only in western cucumber mosaic. But cleared venation, chlorotic spotting, blisterlike elevations, and necrosis occur in all three. The viruses can be distinguished by transferring them to sugar beets; on that host the symptoms are sufficiently distinctive to permit identification. New Zealand spinach (Tetragonia expansa) was experimentally infected with western cucumber mosaic, and the virus was recovered and transferred to White Spine cucumber and sugar beet. The green peach aphid, Myzus perslcae (Sulzer), is the most important vector of the western-cucumber-mosaic, celery-calico, and sugar-beet-mosaic viruses to spinach under natural conditions. The bean or dock aphid, Aphis rumicis Linnaeus, rarely transmits these viruses.