Onion, Allium cepa, is the third most consumed vegetable in the U.S., behind tomato and potato. The per capita consumption of onion in the U.S. is over 20 pounds per year, which has increased 70% over the past 20 years (https://www.onions-usa.org/all-about-onions/consumption). Onion also is one of the most economically important specialty crops with a farm-gate value averaging nearly $1 billion per year over the past 5 years (USDA NASS 2021) and over $70 million in added value after processing. In addition, over 20% of the world’s onion seed is produced in the U.S. and is valued at over $100 million per year. More than 138,000 acres of onions have been harvested annually over the past 5 years and the crop is grown in over 20 states with a majority produced in California, Idaho-Eastern Oregon and Washington in the west, Texas and New Mexico in the south, and Georgia and New York in the east (USDA NASS 2021).

The need as indicated by stakeholders. Onion crops are damaged by a spectrum of pests and pathogens throughout the U.S. For example, infestations of fly maggots (Delia spp.) can reduce plant stands by over 50% if not controlled (Nault et al. 2006), while a new invasive fly pest (Phytomyza gymnostoma) is raising concern (Barringer et al. 2018). Onion thrips (Thrips tabaci) feeding damage can reduce bulb yield by up to 30 to 50% (Fournier et al. 1995; Leach et al. 2020b) and it also spreads pathogens that cause devastating diseases like Iris yellow spot (IYS, caused by Iris yellow spot virus) (Gent et al. 2004, 2006; Bag et al. 2014), Stemphylium leaf blight (SLB, caused by Stemphylium vesicarium) (Leach et al. 2020a) and bacterial bulb rots (Grode et al. 2017, 2019). Multiple fungal and bacterial pathogens can cause onion yield losses in the field and in storage facilities throughout the U.S. (Schwartz and Mohan 2008). Each disease can cause up to 25 to 100% crop loss. The most important fungal diseases include SLB, purple blotch (Alternaria porri), downy mildew (Peronospora destructor), black mold (Aspergillis niger), Botrytis leaf blight (Botrytis squamosa) and neck rot (Botrytis species), Fusarium basal rot (FBR) (Fusarium oxysporum f. sp. cepae), white rot (Sclerotium cepivorum), pink root (Pyrenochaeta terrestris) and powdery mildew (Leveillula taurica). The most important bacterial diseases include sour skin (Burkholderia cepacia), slippery skin (Burkholderia gladioli pv. Alliicola), center rot (Pantoea ananatis and P. agglomerans), leaf streak (Pseudomonas viridiflava), soft rot (Pectobacterium carotovorum and Dickeya spp.), and Enterobacter bulb decay (Enterobacter cloacae). Serious weeds include yellow nutsedge (Cyperus esculentus), ragweeds (Ambrosia spp.), pigweeds (Amaranthus spp.), lamsquarters (Chenopodium album), perennial sowthistle (Sonchus arvensis) and others. Growers continue to abandon onion production in some regions because one or more of these organisms have caused catastrophic losses. Consequently, we propose to address managing the most serious pests, diseases and weeds of onion through the following objectives: 

• Evaluate onion germplasm for resistance to pathogens and insects.


• Investigate the biology, ecology and management of onion insect pests.


• Investigate the biology, epidemiology and management of onion plant pathogens.


• Investigate the biology, epidemiology and management of weedy plant species that impact onion production. 

Importance of the work, and consequences if it is not done. The work proposed is critical for solving the most important pest, disease and weed problems facing the U.S. onion industry. We are not aware of other public or private entities that will be as organized across state borders to solve these problems as the W4008 group, particularly given the successful foundation set by the preceding multistate onion projects (W1008: Biology and Management of Iris yellow spot virus (IYSV) and Thrips in Onions, from 2005-2010; W2008: Biology and Management of Iris yellow spot virus (IYSV), Other Diseases and Thrips in Onions, from 2011-2016; and W3008: Integrated Onion Pest and Disease Management, from 2017 to 2022). The most significant change to our proposed multistate project is that we will include a weed biology and management objective. Similar networking successes are anticipated for weed scientists working in onion cropping systems across the country, just as they have occurred with entomologists and plant pathologists during our previous multistate projects. 

We expect that results from our research and extension activities will continue to contribute significantly to science and agriculture as we communicate new knowledge about the biology, ecology and management of these pests, pathogens and weeds through peer-reviewed publications, presentations at professional meetings, field days, and web-based resources for stakeholders. Consequences of not addressing these significant issues include further reductions in U.S. onion acreage due to limited ability to manage the pests, diseases, and weeds mentioned above, reduced profits as a result of decreased bulb yields, reduced quantities and/or qualities of onion seed produced, greater competition from other regions of onion bulb and seed production in the world, and greater pesticide and fertilizer inputs, as well as potential environmental and human health concerns associated with greater fertilizer and pesticide use. 

Technical feasibility of the research. Participants of our proposed project will include researchers at institutions that have the resources, laboratories, land for research and personnel required to conduct the studies described herein. Project objectives are designed to include short-term, medium-term, and longer-term research studies that should reasonably be completed within the 5-year duration of this project. A majority of the members of this project have a proven track record of effective, collaborative onion research and extension programs, including involvement in the W1008, W2008, and W3008 multistate projects that laid the foundation for the next iteration, the W4008. 

Advantages for doing the work as a multistate effort. The principal advantage of doing this work as a multistate effort is that this proposal builds on three previous, highly successful multistate projects that were described above. Indeed, the W3008 project team was awarded the 2018 Excellence in Multistate Research Award given by the Western Association of Agricultural Experiment Station Directors. We anticipate that participants of our proposed project will continue to include most of those who are leaders in their respective areas of onion breeding, horticulture, entomology, plant pathology, virology, microbiology, and weed science. Past participants have included public and private researchers, extension professionals, onion growers and seed industry personnel throughout the U.S. who have formed productive collaborations. Many of the problems affecting onion production occur in most regions in the U.S., so our project brings together those with similar interests in solving the issues. The proposed research is synergized by interactions this group has developed over the past 17 years, which we anticipate will continue. The research and extension contributions from members in all major regions of onion production in the U.S. adds efficiency, pooled expertise, and synergies that are greater than the sum of each individual research and extension program. At least three multi-state, multi-disciplinary, 4-year proposals funded by the USDA NIFA Specialty Crops Research Initiative were developed as a result of collaborations in the W1008, W2008, and W3008 multistate projects, and we anticipate continued success of this group at garnering such resources to address the pests, diseases, and weed issues of concern to onion stakeholders across the country. 

Likely impacts from successfully completing the work. This project is expected to have positive impacts on the economy, environment and society. The cost of onion production should be reduced through implementation of new management tactics that utilize new onion cultivars with greater resistance to thrips, IYSV and FBR, and reduced inputs such as pesticides and fertilizers. More judicious use of insecticides, fungicides, bactericides, herbicides, action threshold-based pesticide application programs, and optimal pesticide application techniques and strategies that mitigate insecticide, fungicide, and herbicide resistance risks will contribute directly to improved environmental stewardship and sustainability. This project is expected to enhance our understanding of how cultural practices can be optimized to mitigate the risks of these pests, diseases, and weeds, further contributing to reduced expenses and enhanced environmental stewardship. Society will benefit from the training of graduate and undergraduate students as well as post-doctoral associates working with faculty on this project, preparing the next generation of researchers, extension specialists and agricultural professionals in public roles and private industries who will shape the future of production agriculture.