Stuart Reitz at Malheur County Extension reports that iris yellow spot virus was detected at the end of last week in commercial onion fields in Malheur County, Canyon County, Payette County and Washington County. So far, only a few infected plants were found but no widespread outbreaks.
As always, maintaining good thrips management will help limit the spread and severity of the disease. Infective adult thrips spread the virus from plant to plant as well as within a plant. Infective juveniles also can spread the virus within a plant.
In addition to thrips management, minimize stress on onion plants by making sure fields are maintained at an adequate but not excessive fertility level, and that the soil moisture is kept at about the 20 centibar level. This will help reduce the severity of virus symptoms.