Sustainable Solutions to IYSV on Onion Via Grower-Research Partnerships

Sustainable Solutions to IYSV on Onion Via Grower-Research Partnerships

Summary

The combined effects of variety, irrigation system, irrigation criterion, and nitrogen (N) rate on IYSV expression and onion yield and grade were evaluated in 2008. N fertilization at 224 kg/ha failed to improve disease incidence or yield over 112 kg/ha. Drier irrigation criteria (30 kPa) resulted in more severe IYSV symptoms and lower marketable, colossal, and colossal plus super-colossal bulb yield than the wetter irrigation criteria. There were no significant interactions between variety, irrigation criteria, and N rate either year. Some varieties demonstrated tolerance with clearly different performance in the presence of IYSV. Kaolin foliar treatments failed to suppress IYSV.

Objectives/Performance Targets

Maintain onions as a viable part of the PNW family farm crop rotations by reducing the impact of IYSV through the following:

1. Identify onion lines with resistance or tolerance to IYSV.

2. Reduce water stress and heat stress on onions through irrigation systems and irrigation criteria.

3. Determine if added N can help affected onions continue to maintain bulb growth.

4. Synergism among 1-3 above

5. Reduce heat stress by using foliar kaolin clay at peak heat stress

6. Demonstrate all useful findings in growers’ fields. Fully and promptly communicate results via word of mouth, fieldman participation, field days, grower meetings, Internet, national working group meetings, and papers in trade and scientific journals.

The initiatives of our project would be complementary to initiatives of parallel efforts to control onion thrips and isolate over-wintering seed and bulb crops from summer bulb crops.

Accomplishments/Milestones

The onion trials were conducted in 2008 and 2009 as planned. Results from 2008 have been compiled and distributed. Onions from the 2009 season and stored in the 2009-2010 storage season are being graded and the data will be analyzed, reported, and published. Based on the first year of the project, preliminary results indicate the following:

1. Based on “on farm” and “on station” trials, onion varieties have been tentatively identified that are more and less tolerant to IYSV. Some of the apparently tolerant lines were not seriously considered by growers two years ago.

2. Irrigation systems and irrigation criteria have been tested as planned. Small increments of water stress on onion are very detrimental to onion yield and grade in the presence of IYSV. More growers are adopting drip irrigation systems and carefully monitoring soil water tension.

3. Extra N fertilizer does not seem to be of any benefit to help onions continue growing in the presence of IYSV.

4. No interactions have yet been observed between varieties, water stress, and N fertilizer rates.

5. “On farm” attempts to reduce IYSV effects through the application of kaolin clay have not been successful.

6. Information pertinent to IYSV and thrips biology was transferred to growers, other onion industry parties, and the public through numerous meetings, field days, publications, and the Internet. Results have been effectively communicated by grower and fieldman participation in the project planning and evaluation of results, field days for growers July 8 and August 25, 2009, grower meetings in February 2009, Internet websites, and results being retold by the reporters of Onion World.

7. Journal articles and an extension brochure need to be written. The extension brochure would be a synthesis of information developed to date including ways to avoid IYSV pressure. A journal article would cover the difference in IYSV symptoms and onion performance with small increments of water stress.

Impacts and Contributions/Outcomes

IYSV seems to be less pronounced, although it is too early to tell. The benefits may be related to the current project.

1. More growers are adopting onion varieties with apparent greater tolerance to IYSV. Seed availability is still a limiting factor for these new varieties.

2. Due to better knowledge of the transmission of IYSV, growers are breaking the natural green bridge keeping IYSV pressure high from one production year to the next. Less of the Idaho-Oregon onion bulb production area combines summer bulb production with over-wintering and seed production crops. Growers are also practicing more vigilance in destroying onion culls. But some growers are still vexed with over-wintering onion bulb or seed fields close to their summer production fields.

3. More growers are adopting drip irrigation and adopting careful irrigation scheduling. These carefully irrigated onion crops seem to be suffering less from IYSV.

4. More growers are using soft insecticides to control trips early in the season, allowing natural predators to help control thrips, at least at the beginning of the summer.

Collaborators: