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A number of plant viruses were isolated from diseased cucurbits in Arizona during 1982 -85. Watermelon mosiac virus 2, cucumber mosaic virus, and squash mosaic virus are previously recognized viral pathogens in Arizona and in most years are not considered economically threatening to cucurbit production. Three newly described plant viruses (lettuce infectious yellows, watermelon curly mottle and zucchini yellow mosaic) however, have the potential to, or already have, incited serious epidemics in Arizona. Losses are heaviest with these diseases when insect vector levels build up early in the growing season and plants become infected during critical developmental stages.