Biology and Management of Iris Yellow Spot Virus (IYSV), Other Diseases, and Thrips in Onions (from W1008)

<p>NON-TECHNICAL SUMMARY:<br/> Onion (Allium cepa) is an economically important crop in the U.S., generating over 900 million dollars annually in farm receipts from 2005 to 2010. U.S. onion production area ranges from 60,000 to 70,000 hectares annually, with over 80% of the summer production (50,000 hectares) in the western states. Worldwide, 53 million metric tons of onion bulbs are harvested annually from nearly 3 million hectares. A significant portion of the U.S. and world supply of onion seed is produced in the western U.S., primarily in the Pacific Northwest. Onion thrips is the most serious pest of onion worldwide and it has become an even greater threat to onion as a vector of IYSV. Although onion thrips is the most common thrips pest of onion in the U.S., the western flower thrips (Frankliniella occidentalis) and the tobacco thrips (Frankliniella fusca) are also
major pests of onion in parts of the western U.S. and southeastern U.S., respectively. Infestations of thrips in onion fields are managed primarily with frequent insecticide applications. In spite of chemical-intensive management, thrips continue to cause significant and increasing damage to onion because of widespread insecticide resistance to older insecticides that are still widely used by the. Therefore, thrips are a primary constraint to continued productive and sustainable onion production. Newer chemistries for thrips control continue to be released and incorporated into Integrated Pest Management (IPM) strategies. In addition to feeding injury caused by thrips, Iris yellow spot virus (IYSV), which is vectored by onion thrips, has emerged as a devastating new disease of onion. It causes widespread disease of onion and other Allium species and has been observed throughout the U.S.
in bulb onion, chive, leek and garlic crops. Management of IYSV is challenging. Current management strategies include selection of cultivars less susceptible to the disease and/or the vector, increased and uniform plant population, selection of transplants free of IYSV and thrips, elimination of volunteer onions from previous crops and weeds during current cropping season, and separation of onion bulb and seed crops to break the green-bridge reservoirs of the thrips vector and the virus, Many growers also have implemented intensive thrips insecticide programs, which may provide some suppression of the disease. In spite of advances made in management of IYSV and thrips during the past 5 years the projected economic impacts of IYSV and thrips in the U.S. could reach 60 million dollars (10 percent loss) to 90 million dollars (15 percent loss). The use of 3 to 5 additional sprays for thrips
control on 48,500 hectares of Allium crops per year adds 7.5 to 12.5 million dollars and uncalculatable environmental costs. The rapid and international spread of this disease emphasizes the need to continue to develop economical and effective IPM strategies. This project seeks to mitigate onion loss to thrips, virus, and other diseases to a multifaceted research and education program.
<p>APPROACH:<br/> We will continue to uniformly evaluate and report the reactions of onion entries (advanced breeding lines, cultivars, germplasm accessions) when exposed to IYSV and thrips populations under field and controlled conditions at cooperating sites with varying environmental conditions that support short-day, intermediate-day, and long-day onion types. Additional screening and identification of promising materials will continue to be promoted for use in onion cultivar improvement efforts by public and private onion breeders at cooperating sites throughout the U.S. It is important that cultivars that are selected for tolerance to IYSV and/or onion thrips are not especially susceptible to other diseases of onions, which could limit their usefulness commercially. Collaborators will conduct field, greenhouse and laboratory studies that will improve our understanding
about thrips biology and IYSV epidemiology and lead to better management strategies for thrips and IYSV. These management strategies will be evaluated in trials at field stations and with cooperating growers. Dispersal of onion thrips in onion ecosystems is a key biological parameter that is not well known. Thrips dispersal will be examined through conventional sampling techniques such as visual counts of thrips in the surroundings of onion fields and on onion plants and numbers of adults captured on sticky cards. Cultural control tactics for thrips are needed and recent studies have identified reduced levels of nitrogen at planting as beneficial in reducing thrips populations without sacrificing yield. Research will continue to identify the overall role that nutrient management has on thrips populations. Use of live mulches, cover crops and foliar applications of kaolin are also among
the cultural tactics that will be explored. As onion growers use more selective insecticides to manage thrips, natural thrips predators have become more common in onion fields. Research will identify natural enemy species that reduce thrips populations and strategies that will enhance natural predator populations and when these predators will have the greatest impact on suppressing thrips infestations. Detect foodborne pathogens associated with harvested onions: The DNA macroarray mentioned above is slated to include the detection of Salmonella spp. and E. coli, certain strains of which are human pathogens and can pose food safety risks. If either of these genres of bacteria is detected using the DNA macroarray, further tests can be conducted to determine if the strains pathogenic to humans are present and if they pose a food safety risk. A more integrated point of exchange between
researchers, growers and other interested parties will be developed and expanded. W2008 members will continue to share results from this project and learn from colleagues involved with various research and extension projects.
<p>PROGRESS: 2012/10 TO 2013/09<br/>Target Audience: Onion growers and shippers Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided? Two undergraduate students learned about onion research and helped write reports. How have the results been disseminated to communities of interest? Findings from this research has been posted on websites, published in newsletters, presented at various meetings, and communicated directly with growers and other industry personnel. This information has led to the adoption of more effective management programs in onion cropping systems. 1. More growers are adopting onion varieties with greater tolerance to IYSV. 2. More growers are adopting drip irrigation and maintaining better management of soil moisture. The onions grown with drip irrigation and careful irrigation
scheduling tended to have less severe problems with IYSV. 3. Growers continue to improve their use of insecticide rotation programs through the growing season. Research trials have led to the identification of effective season-long insecticide use programs. These programs have enabled growers to successfully manage thrips over a single growing season and reduce the risk of insecticide resistance developing. 4. Due to better knowledge of the transmission of IYSV, fewer growers are planting over-wintering onions. With fewer overwintering onions and better cull onion disposal, growers are breaking the natural green bridge keeping IYSV pressure high from one production year to the next. Some growers continued to suffer IYSV related yield losses due to over-wintering onion bulb or seed fields close to their summer production fields. What do you plan to do during the next reporting period to
accomplish the goals? We plan to continue the same activities reported above in our accomplishment of goals.