The 2010 ASHS Annual Conference

 Kristie Buckland¹, Jennifer Reeve¹, Daniel Drost¹, and Diane Alston²

 Utah State University
¹Department of Plants, Soils and Climate, 4820 Old Main Hill, Logan, UT
²Department of Biology, 5305 Old Main Hill, Logan, UT

Onion production in the western United States suffers significant damage from iris yellow spot virus (IYSV).  Since IYSV is thrips vectored and primary control options include heavy pesticide use, there has been an increase in pesticide resistance and virus spread.  The objectives of this study were to identify crop management strategies to enhance onion productivity and suppress thrips and IYSV.  Three fertility programs, two crop rotation schemes and three trap crops were tested for their effects on onion yield, thrips density and IYSV.  Thrips adults, nymphs and eggs populations were monitored from whole plant and leaf samples collected in the various N treatments and trap crops.  Reduced nitrogen input (134.5 kg N/ha, one-third grower rate), resulted in no significant reduction in yield.  There was a decrease in soil microbial activity, as measured by dehydrogenase activity in treatments receiving the high rate of N fertilizer (392 kg N/ha).  Both thrips adult and egg densities were greater in onions fertilized with the high N rate, particularly when rotated with wheat.  Both lacey phacelia and carrots were more attractive than onions early in the season.  However, later in the season, trap crops were less effective in attracting thrips.  There were no treatment effects on IYSV infection as measured by ELISA testing; however, overall IYSV incidence was low.  Early results suggest that reduced nitrogen input coupled with corn/onion rotation reduced attractiveness of onions to thrips and created a more favorable environment for microbial activity while sustaining onion yields.  While the early attractiveness of trap crops looks promising, further investigation is needed to determine if this is a suitable alternative thrips management strategy for onion.