Changes in the spatial distribution of onion thrips (Thrips tabaci) and iris yellow spot virus in onion fields over time

Iris Yellow Spot Virus (IYSV), an invasive virus first detected in the United States in 1989, spread throughout the southwest and western states during early 2000 causing significant damage to onion crops. IYSV was first detected in New York in 2006, but was confirmed to be present in all major onion growing regions of New York in 2007, suggesting it may have established prior to 2006. The only confirmed vector of IYSV is the onion thrips, Thrips tabaci, and T. tabaci is the dominant thrips species in onions in New York. Onions are primarily grown as a fresh market bulb crop in New York, requiring the virus to be re-introduced into fields each year. Analyses of changes in the spatial distribution of onion thrips and IYSV over time in onion fields will be presented. Dramatic increases in IYSV infection rates occur late in the season and may be due to increased primary spread resulting from harvest of nearby fields. Management options for minimizing IYSV, including early removal of volunteer onions, spatially concentrating crops with similar harvest dates, and late season management of thrips, will be discussed.