Final Report for SW08-121
Project Information
Growers, fieldmen, extension and research personnel cooperated to establish priorities to address Iris Yellow Spot Virus (IYSV) on onion. Trials were conducted by growers, extension and researchers testing varieties, irrigation systems, irrigation criteria, nitrogen fertilizer rates and kaolin clay on IYSV expression, onion thrips and onion bulb yield and quality. Extra nitrogen fertilizer, sprinkler irrigation or kaolin clay failed to reduce IYSV or improve onion yield. More growers adopted drip irrigation, better irrigation scheduling, tolerant onion varieties and more effective thrips control that showed positive responses in grower and station trials.
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, field personnel 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 crop from the summer bulb crop.
Although IYSV was first identified locally in the Treasure Valley of Oregon and Idaho as an onion disease in 1989, damage seemed to be confined to the overwintering onion seed crop. By the early 2000s, growers were experiencing substantial onion bulb losses, apparently due to IYSV. Part of the increased effect of IYSV may have been related to increases in onion thrips, the vector of IYSV. Onion thrips have been rapidly developing resistance to insecticides used in their control.
Long-term, IYSV may be eliminated as an important factor through breeding resistant onion varieties. In the short-term, growers need more immediate options.
Growers had noted that small variations in soil preparation that made irrigation more difficult might be aggravating bulb losses to IYSV, suggesting the importance of waiting for drier soil for tractor operations and the importance of precise irrigation scheduling.
Further growers hypothesized that:
1) Sprinkler irrigation might help control thrips,
2) Extra N fertilizer might help onions grow out of IYSV symptoms, and
3) Kaolin clay might help suppress thrips or at least cool onions so they expressed fewer IYSV symptoms.
We hypothesized that lower water stress might help keep the soil and onions cooler and reduce IYSV expression. Varieties, although not truly resistant to IYSV, might vary in their tolerance to IYSV. These ideas were tested in growers’ fields and in interactive trials at the Oregon State University Malheur Experiment Station to identify practices that could be used immediately by growers to reduce losses from IYSV.
Cooperators
Research
Grower demonstration trials
Growers implementing kaolin clay, new varieties, drip irrigation systems, irrigation scheduling or insect control through their drip irrigation systems made side by side comparisons in their own fields with no replications.
Replicated variety performance on farm
Replicated variety trials were conducted in growers’ fields and on the OSU Malheur Experiment Station to identify superior onion lines and to try to find onions with some tolerance to IYSV. The complete materials and methods are recorded in the corresponding reports, and the methods included valid statistical designs. Onion thrips were carefully counted and IYSV severity was noted.
Interactive management trials
Trials that included irrigation systems and irrigation criteria, nitrogen rates and varieties were conducted at the OSU Malheur Experiment Station. Main plots were irrigation systems and irrigation criteria. N rates were split plots, and varieties were split-split plots. Many disease, thrips, soil water potential, soil temperature, bulb yield and bulb quality measurements were made. The complete materials and methods are included in the reports.
- Shock, C.C., E.B.G. Feibert, L.D. Saunders, L.B. Jensen, K. Mohan, R. Sampangi and H. Papp. 2011. 2010 onion variety trials. p 14-22. In Shock C.C. (Ed.) Oregon State University Agricultural Experiment Station, Malheur Experiment Station Annual Report 2010, Department of Crop and Soil Science Ext/CrS 132.
- Shock, C.C., E.B.G. Feibert, L.D. Saunders, L.B. Jensen, S.K. Mohan, R.S. Sampangi and H. Pappu. 2011. Management of onion cultural practices to control the expression of Iris Yellow Spot Virus. p 23-41. In Shock C.C. (Ed.) Oregon State University Agricultural Experiment Station, Malheur Experiment Station Annual Report 2010, Department of Crop and Soil Science Ext/CrS 132.
- Shock, C.C., E.B.G. Feibert and J. Taberna. 2011. Effect of timing of harvest on onion yield and storability. p 70-76. In Shock C.C. (Ed.) Oregon State University Agricultural Experiment Station, Malheur Experiment Station Annual Report 2010, Department of Crop and Soil Science Ext/CrS 132.
- Onion thrips were counted regularly in main plots and split plots.
The onion trials were conducted in 2008, 2009 and 2010 as planned. Results from all three years have been compiled and distributed to growers and the public. The results indicate the following:
1. Based on “on farm” and “on station” trials, onion varieties have been identified that are more and less tolerant to IYSV. The 2009 onion variety trial strongly sorted varieties for IYSV since the infection rate was severe. Heavily infested bulbs failed to mature properly and were more subject to decomposition in storage.
2. Irrigation systems and irrigation criteria were tested as planned. Small increments of water stress on onion were very detrimental to onion yield and grade in the presence of IYSV in 2008. In both 2009 and 2010, the IYSV pressure on the onions in the irrigation trial site was less than in 2008, and the effects of water stress were less dramatic. Forty-two percent of growers’ onion fields have been converted to drip irrigation with irrigation scheduling being carefully controlled through the monitoring of soil water tension.
3. The growers’ notion that sprinkler irrigation would aid in the reduction of onion thrips and IYSV has not been substantiated. There was little difference in thrips pressure between irrigation systems at most measurement dates.
4. At the beginning of the project, growers presumed that extra N fertilizer might help onion overcome IYSV, but N fertilization at 224 kg/ha failed to reduce IYSV disease incidence or improve onion bulb yield over 112 kg/ha all three years.
5. Few interactions were observed between varieties, irrigation systems or irrigation criteria and N fertilizer rates. There were interactions between the irrigation treatments and varieties in bulb yield and bulb grade in 2010.
6. “On farm” attempts to reduce IYSV effects through the application of kaolin clay failed, and growers stopped trying this option.
7. The project has continued to effectively transfer information pertinent to IYSV and thrips biology 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 field personnel participating in the project planning and evaluation of results, the most recent field days for growers on July 13, 2011 and August 30, 2011, the annual grower meeting on February 1, 2011, our internet web site, and the results being reported in Onion World.
8. Since irrigation scheduling emerged an a simple and cost effective way to mitigate the effects of IYSV, an extension brochure was written, published and widely distributed on irrigation scheduling of onion. A more general extension brochure on managing IYSV has been drafted.
9. A journal article has been published that mentions the difference in IYSV symptoms and onion performance with small variations in incremental water stress. This article was written with resources other than those from Western SARE.
Shock, C.C. and F.-X. Wang. 2011. Soil water tension, a powerful measurement for productivity and stewardship. HortScience 46: 178-185.
An additional journal article specifically on the Western SARE work is in a draft form.
- Although onions grown with 100 lb N/acre/year did not look as vigorous as those grown with 200 lb N/acre/year, the higher N rate did not help onions overcome IYSV, not did it result in increased onion bulb yield or grade.
- Shock, C.C., E.B.G. Feibert, L.D. Saunders, L.B. Jensen. 2010. Oregon 2009 progress on the biology and management of Iris Yellow Spot Virus (IYSV) and thrips in onions. Written report 12 January 2010 to W1008, the national IYSV working group.
- Onions grown with an irrigation scheduling criterion of 30 cb (30 kPa) had lower yields (2008, 2009, and 2010) and greater symptoms of IYSV (2008) than onions grown at wetter criteria.
Social and Economic Impacts and Outcomes
Damage of IYSV has been less pronounced region-wide in 2010 and 2011. It is hard to tell if the benefits are related to the current project or fluctuations in weather and thrips populations. Also the current project resulted in substantial educational efforts that covered all aspects of IYSV, so it is difficult to separate the positive effects of the current research and field demonstrations from the enhanced education about thrips control and green bridge control of IYSV.
Increasing numbers of growers are adopting drip irrigation and careful irrigation scheduling to avoid water stress. These carefully irrigated onion crops seem to be suffering less from IYSV. Drip systems are facilitating thrips control due to efficient injection of labeled insecticides.
More growers are using soft insecticides to control trips and starting their spray programs earlier in the season, allowing natural predators to help control thrips, at least at the beginning of the summer. Insecticides are used in rotation with the products detrimental to thrips predators used later in the growing season. Insecticide use strategies proven effective in our replicated field tests have been widely adopted.
A green bridge of IYSV on overwintering onion bulb or seed fields continues to plague certain growers, and they suffer IYSV-related yield losses due to close proximity of overwintering crops to their summer production fields. Most growers are avoiding green bridge problems by careful eradication of volunteer onions from one year to the next. Due to better knowledge of the transmission of IYSV, fewer growers are planting overwintering onions. With fewer overwintering onions and better cull onion disposal, more growers are breaking the green bridge that keeps IYSV pressure high from one production year to the next.
Growers are adopting onion varieties with greater tolerance to IYSV.
Scientific Outcomes
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, 2009 and 2010. In 2008, drier irrigation criteria (30 kPa) resulted in more severe IYSV symptoms. In both 2008 and 2010 the drier irrigation criteria resulted in lower marketable, colossal and colossal plus super-colossal bulb yield than the wetter irrigation criteria. In 2009 the wettest irrigation criteria reduced marketable yields. The 2009 season proved to be helpful in identifying locally-adapted varieties with tolerance to IYSV. Growers presumed that sprinkler irrigation would be beneficial in controlling thrips, and hence IYSV, but only weak positive trends for thrips control were observed in 2008, and no suppression of IYSV; in fact sprinkler-irrigated onion yielded less than drip-irrigated onion at the same irrigation criteria over the three years. Growers presumed that extra N fertilizer might help onion overcome IYSV, but N fertilization at 224 kg/ha consistently failed to reduce IYSV disease incidence or improve onion bulb yield over 112 kg/ha. There were no significant interactions between variety, irrigation criteria and N rate in 2008 or 2009, but there were interactions between variety and irrigation in 2010. Kaolin foliar treatments failed to suppress IYSV and have been dropped by growers.
Research Outcomes
Education and Outreach
Participation Summary:
1. PowerPoint presentations to growers and field personnel at annual grower association meetings
Shock*, C.C., E.B.G. Feibert, L.D. Saunders, L.B. Jensen, S.K. Mohan, R.S. Sampangi and H. Pappu. 2011. Irrigation, N fertilization and varietal effects on the expression of Iris Yellow Spot Virus in onion. Malheur County, Oregon and Idaho Onion Growers Annual Meeting. February 1, 2011. Ontario, OR.
Shock*, C.C., E.B.G. Feibert, L.D. Saunders, L.B. Jensen, K. Mohan, R. Sampangi and H. Papp. 2011. Onion variety trial report, 2010. Malheur County, Oregon and Idaho Onion Growers Annual Meeting. February 1, 2011. Ontario, OR.
Shock, C.C., E.B.G. Feibert*. 2011. Effect of timing of harvest on onion yield and storability. Malheur County, Oregon and Idaho Onion Growers Annual Meeting. February 1, 2011. Ontario, OR.
2. Published annual reports for growers
Shock, C.C., E.B.G. Feibert, L.D. Saunders, L.B. Jensen, S.K. Mohan, R.S. Sampangi and H. Pappu. 2011. Management of onion cultural practices to control the expression of Iris Yellow Spot Virus. p 23-41. In Shock C.C. (Ed.) Oregon State University Agricultural Experiment Station, Malheur Experiment Station Annual Report 2010, Department of Crop and Soil Science Ext/CrS 132. http://www.cropinfo.net/AnnualReports/2010/OnionIYSV.html
Shock, C.C., E.B.G. Feibert, L.D. Saunders, L.B. Jensen, K. Mohan, R. Sampangi and H. Papp. 2011. 2010 onion variety trials. p 14-22. In Shock C.C. (Ed.) Oregon State University Agricultural Experiment Station, Malheur Experiment Station Annual Report 2010, Department of Crop and Soil Science Ext/CrS 132. http://www.cropinfo.net/AnnualReports/2010/OnionVariety.html
Shock, C.C., E.B.G. Feibert and J. Taberna. 2011. Effect of timing of harvest on onion yield and storability. p 70-76. In Shock C.C. (Ed.) Oregon State University Agricultural Experiment Station, Malheur Experiment Station Annual Report 2010, Department of Crop and Soil Science Ext/CrS 132. http://www.cropinfo.net/AnnualReports/2010/OnionTiming.html
3. Oral presentations to growers at field days, no paper copy:
Shock*, C.C., E.B.G. Feibert*, L.D. Saunders, K.S. Mohan, R. Sampangi, and H. Pappu. 2011. Management of IYSV. Summer Farm Festival and Annual Field Day, OSU Malheur Experiment Station. 13 July 2011. Ontario, OR.
4. Oral presentations and written reports to national meetings and working groups:
Shock*, C. C., L.B., Jenson, E.B.G., Feibert, and L.D. Saunders, 2010. Oregon report to the W-1008 committee: IYSV and thrips. December 6, 2010. Sparks, Nevada.
Shock*, C.C., E.B.G. Feibert, L.B. Jensen, and P. Richerson. 2010. How groundwater improved while onion production increased. 2010. National Allium Research Conference. December 7-8, 2010. Sparks, Nevada.
Shock*, C. C., Feibert, E.B.G., Saunders, L.D., Jenson, L.B., Mohan, K., R.S. Sampangi and Pappu, H. 2010. Irrigation, N fertilization and varietal effects on the expression of Iris Yellow Spot Virus in onion. 2010. National Allium Research Conference. December 7-8, 2010. Sparks, Nevada.
Feibert*, E.B.G., C.C. Shock, C.C., and J. Taberna. 2010. Effect of harvest timing and maturity on onion yield and storability. 2010. National Allium Research Conference. December 7-8, 2010. Sparks, Nevada.
- Feibert*, E.B.G., C.C. Shock, C.C., and J. Taberna. 2010. Effect of harvest timing and maturity on onion yield and storability. 2010. National Allium Research Conference. December 7-8, 2010. Sparks, Nevada.
- Shock*, C. C., Feibert, E.B.G., Saunders, L.D., Jenson, L.B., Mohan, K., R.S. Sampangi and Pappu, H. 2010. Irrigation, N fertilization and varietal effects on the expression of Iris Yellow Spot Virus in onion. 2010. National Allium Research Conference. December 7-8, 2010. Sparks, Nevada.
- Shock*, C.C., E.B.G. Feibert, L.B. Jensen, and P. Richerson. 2010. How groundwater improved while onion production increased. 2010. National Allium Research Conference. December 7-8, 2010. Sparks, Nevada.
- Shock*, C.C., E.B.G. Feibert, L.D. Saunders, L.B. Jensen, K. Mohan, R. Sampangi and H. Papp. 2011. Onion variety trial report, 2010. Malheur County, Oregon and Idaho Onion Growers Annual Meeting. February 1, 2011. Ontario, OR.
- Shock, C.C., E.B.G. Feibert*. 2011. Effect of timing of harvest on onion yield and storability. Malheur County, Oregon and Idaho Onion Growers Annual Meeting. February 1, 2011. Ontario, OR.
- Shock*, C.C., E.B.G. Feibert, L.D. Saunders, L.B. Jensen, S.K. Mohan, R.S. Sampangi and H. Pappu. 2011. Irrigation, N fertilization and varietal effects on the expression of Iris Yellow Spot Virus in onion. Malheur County, Oregon and Idaho Onion Growers Annual Meeting. February 1, 2011. Ontario, OR.
- Shock*, C.C., E.B.G. Feibert, L.D. Saunders, L.B. Jensen, H.R. Pappu, S.K. Mohan, and R.S. Sampagni. 2009. Cultural practices to reduce the expression of Iris Yellow Spot Virus. American Society of Horticultural Science Annual Conference, 25 – 28 July, 2009, St. Louis, Missouri.
Education and Outreach Outcomes
Areas needing additional study
1. Not all of the sources of overwintering IYSV have been identified. Overwintering weeds may be harboring IYSV, but our attempts to identify such weeds have failed.
2. Some growers still grow overwintering onion bulb and seed crops in close proximity to summer bulb crops, with predictable problems and losses.
3. Wider adoption of drip irrigation and irrigation scheduling would help assure grower yields.
4. Comparisons of thrips control systems by foliar application and by injection through the drip tape seem warranted. Insecticide application through the drip tape may be more effective.