MONITORING ONION PESTS ACROSS THE TREASURE VALLEY Stuart Reitz, Malheur County Extension, Oregon State University, Ontario, OR, 2016
Introduction Onion growers continue to be challenged by how to manage thrips and iris yellow spot virus (IYSV) that thrips vector. The Idaho-Eastern Oregon region has a range of different subregions, and thrips and virus pressure varies across those subregions. A number of growers have asked for assistance in monitoring pest pressure within their particular districts so they can make better informed management decisions. My objective is to provide growers with regional assessments of pest abundance in commercial fields.
Methods Six commercial fields in each of six growing districts were monitored for thrips and IYSV on a weekly basis. Averages of adult and immature thrips, and IYSV incidence for each district were reported to growers, crop advisors, and others each week from April to August.
Results and Conclusions Adult thrips were first detected in fields by May 3, with immature thrips first found the following week. The highest early season populations were in transplanted onions. IYSV was first found by June 2 (although it was found in volunteer onions before then). Thrips populations varied across the growing regions and fluctuated depending on insecticide applications (Fig. 1). Fields on the Oregon Slope tended to have the fewest thrips and lowest incidence of IYSV (Figs. 1 and 2). Fields in Nyssa and Ontario, Oregon, and Fruitland and Parma, Idaho, had the highest incidence of IYSV, with the earliest outbreaks occurring in Fruitland/Parma.
Monitoring Onion Pests Across the Treasure Valley 120 Seasonal Trends of Adult Thrips 18
16
14
12
10
8
6 Mean No.Adult Thrips/Plant 4
2
0 4/26 5/3 5/10 5/17 5/24 5/31 6/7 6/14 6/21 6/28 7/5 7/12 7/19 7/26 8/2
Oregon Slope/Weiser Vale Ontario Nyssa Adrian Fruitland/Parma
Seasonal Trends of Immature Thrips 60
50
40
30
20 Mean No. Immature Thrips/Plant Immature No. Mean 10
0 4/26 5/3 5/10 5/17 5/24 5/31 6/7 6/14 6/21 6/28 7/5 7/12 7/19 7/26 8/2
Oregon Slope/Weiser Vale Ontario Nyssa Adrian Fruitland/Parma
Figure 1. Seasonal trends for adult (top) and immature thrips (bottom) from commercial onion fields across different growing areas of the Treasure Valley. Values are the mean number of thrips per plant for each area.
Monitoring Onion Pests Across the Treasure Valley 121 Seasonal Trends for Incidence Of IYSV 100%
80%
60%
40%
20% Mean Percentage Infected Plants/Field
0% 4/26 5/3 5/10 5/17 5/24 5/31 6/7 6/14 6/21 6/28 7/5 7/12 7/19 7/26 8/2
Oregon Slope/Weiser Vale Ontario Nyssa Adrian Fruitland/Parma
Figure 2 Seasonal trends for Iris yellow spot virus from commercial onion fields across different growing areas of the Treasure Valley. Values are the mean percentage of infected plants per field for each area.
Monitoring Onion Pests Across the Treasure Valley 122