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Onion (Allium cepa) varieties for commercial production in eastern Oregon and southwestern Idaho are evaluated annually in replicated trials conducted at the Malheur Experiment Station, Oregon State University, near Ontario, Oregon. Characteristics evaluated include bulb yield, market grade, and the frequency of single centers. After the emergence of iris yellow spot virus (IYSV) as a threat to commercial onion production in the early 2000s, onion varieties at the Malheur Experiment Station have been evaluated for virus symptoms since 2004. Varieties showed differences in the severity of IYSV symptoms each year. Symptom severity increased over the years from 2004 to 2006, and variety virus ratings showed a strong negative correlation of severity with yield in 2005 and 2006. Marketable yield after 3 months of storage averaged 781, 534, and 551 cwt/acre in 2004, 2005, and 2006, respectively. Averaging over varieties, yield of bulbs larger than 4 inches in diameter was 438 cwt/acre, 56 cwt/acre, and 76 cwt/acre, and the average virus severity ratings were 1.1, 1.3, and 2.7 in 2004, 2005, and 2006, respectively. A few varieties showed a combination of high yield, large bulb size, low incidence of virus symptoms, and a predominance of single-centered bulbs. With the prevalence of IYSV, variety tolerance to IYSV has become an important production factor in the Treasure Valley. [ABSTRACT FROM AUTHOR]