BIOLOGY AND MANAGEMENT OF IRIS YELLOW SPOT VIRUS (IYSV), OTHER DISEASES, AND THRIPS IN ONIONS (FROM W1008)

Onion is an economically important crop in the U.S., generating over 900 million dollars annually in farm receipts from 2005 to 2010. U.S. onion production area ranges from 60,000 to 70,000 hectares annually, with over 80% of the summer production in the western states (NASS, 2010). Worldwide, 53 million metric tons of onion bulbs are harvested annually from nearly 3 million hectares. A significant portion of the U.S. and world supply of onion seed is produced in the western U.S., primarily in the Pacific Northwest (PNW). Onion thrips is the most serious pest of onion worldwide and it has become an even greater threat to onion as a vector of IYSV (Gent et al. 2004). In addition to feeding injury caused by thrips, Iris yellow spot virus (IYSV), which is vectored by onion thrips, has emerged as a devastating new disease of onion. In addition, more than 20 different bacterial and fungal pathogens cause onion losses under field and storage conditions. Each of these diseases can cause up to 50% crop loss, and stakeholders have requested IPM assistance from projects including the W1008. A total loss can be incurred if affected commercial onion loads are refused by buyers and have to be dumped (Schwartz and Mohan, 2008). The W2008 project is designed to develop and improve IPM approaches to managing pests that threaten the sustainability of the U.S. onion industry. In PA, efforts are being directed towards identifying potential sources of the pathogens (transplants, weeds, soil, etc.) for the bacteria most commonly associated with yield losses of onion. Management of bacterial diseases will ultimately require an IPM approach. In NY and PA, extensive surveys of commercial onion fields are also being used to gain a better understanding of the environmental and production conditions (e.g. nitrogen fertility) that favor bacterial disease development, which will facilitate the implementation of a more targeted IPM program. Techniques will be developed to consistently initiate bacterial infection in the laboratory, controlled environment chambers and field to facilitate the evaluation of potential control materials and strategies. We envision that such studies also would increase our understanding of the epidemiology of bacterial pathogens of onion for which only scant information is available. Research on the use of cultural practices to manage bacterial diseases including narrow plant spacing, alternative mulch types and reduced nitrogen fertility will continue. Biological and chemical materials will be investigated that have potential to control bacterial decay through reducing populations of pathogens or enhancing the resistance of onions. Schedules for their application will be developed and their use incorporated into an IPM program. Adoption of these practices to manage onion thrips, IYSV and bacterial pathogens by onion producers will increase the profitability and sustainability of the U.S. onion industry.