- Vegetables: onions
- Crop Production: application rate management, tissue analysis
- Education and Training: demonstration, extension, farmer to farmer, on-farm/ranch research, participatory research
- Pest Management: chemical control, cultural control, economic threshold, field monitoring/scouting
- Production Systems: holistic management
- Soil Management: soil analysis
- Sustainable Communities: sustainability measures
Loss of onion yield and grade to thrips-transmitted iris yellow spot virus (IYSV) is an immediate economic crisis for onion growers in the western states, especially in the Pacific Northwest (PNW) (Gent et al., 2006). Our best chances to reduce the effects of IYSV are to plant tolerant varieties, minimize stress, isolate fields from IYSV and control thrips. Much needs to be learned to implement such a program and maintain onion as a viable part of a sustainable crop rotation. We have documented sharp losses in onion yield and grade related to IYSV symptom severity in 2005 and 2006 (Shock, C.C., E.B.G. Feibert, L.B. Jensen, S.K. Mohan, and L.D. Saunders. 2008. Onion variety response to iris yellow spot virus. HortTechnology. 18:539-544).
IYSV is transmitted by onion thrips. Thrips play a critical role in virus outbreaks, as the virus is not known to be transmitted by seed. Our working hypothesis is that plant stress has a significant impact on onions' ability to withstand losses from thrips feeding and IYSV. There is uncertainty whether water stress or heat stress is most closely related to the negative expression of IYSV. Determining how to manage stress to reduce IYSV disease expression will help growers minimize the impact of IYSV and utilize their insecticide programs more effectively.
Our grower panel has observed that onions grown with drip systems have less IYSV symptoms and fewer negative yield impacts than onions grown with furrow irrigation, which suggests a role for careful management of soil water to reduce the expression and impact of IYSV. Growers have also observed that onions irrigated in center pivot sprinkler irrigation may have lower thrips pressure. Growers have observed that onions planted in poorly prepared soils that become difficult to irrigate result in onions that are more prone to losses from IYSV, suggesting again that irrigation management following proper soil preparation is key to limiting IYSV expression. Are these observations just a matter of chance or do they constitute a sustainable IPM strategy to manage IYSV?
Our project addresses Western SARE goals by building environmentally sustainable options to reduce the impacts of IYSV and stimulating the actions of breeders to reduce the long-term risks of IYSV. Our objectives examine the interaction of irrigation systems, irrigation criteria, onion cultivar, N management and other factors to reduce stress. We incorporate grower and colleague participation and input in all phases. Experimental designs on the station include full factorial experiments with state-of-the-art irrigation automation. Strip trials on growers’ fields will have replicated sampling and will be subjected to appropriate statistical analyses. Our research approach uniquely utilizes and builds on the existing synergies among growers, research and extension personnel across various disciplines (agronomy, entomology, plant pathology and virology) and states (ID, OR and WA).
Grower involvement is crucial to the success of the proposed research, which will assure validation of findings and adoption of effective practices. Growers in the region (Idaho-Oregon Onion Growers Association and Pacific Northwest Vegetable Association) identified IYSV as a top priority, and the involvement of leading growers (and grower association leaders of Oregon, Idaho and the PNW) will facilitate effective and regular evaluation, outreach, education and positive impacts. Close association with fieldmen, trade journals and national onion working groups will help disseminate results.
Project objectives from proposal:
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 numbers 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.