Onion Systems Management Strategies for Crop Nutrition, Weeds, Thrips, and Iris Yellow Spot Virus

Project Overview

Project Type: Research and Education
Funds awarded in 2013: $169,299.00
Projected End Date: 12/31/2016
Region: Western
State: Utah
Principal Investigator:
Dr. Diane Alston
Utah State University

Annual Reports

Information Products


  • Agronomic: corn, wheat
  • Vegetables: onions


  • Crop Production: crop rotation, application rate management, tissue analysis
  • Education and Training: decision support system, demonstration, extension, farmer to farmer, focus group, networking, on-farm/ranch research, participatory research, workshop
  • Farm Business Management: whole farm planning, budgets/cost and returns, agricultural finance, risk management
  • Pest Management: biological control, chemical control, cultural control, disease vectors, field monitoring/scouting, integrated pest management, prevention, sanitation, weed ecology
  • Production Systems: agroecosystems, holistic management
  • Soil Management: soil analysis, nutrient mineralization, soil microbiology, organic matter, soil quality/health
  • Sustainable Communities: sustainability measures

    Proposal abstract:

    Crop management choices and pressure from primary pests [Iris yellow spot virus (IYSV), thrips and weeds] are key drivers in the profitability, sustainability and social responsibility of onion production worldwide. In the western U.S.(55,233 acres of onion planted in 2012, National Onion Association), conventional onion growers rely on high inputs of synthetic fertilizers and high-risk insecticides which have increased pest resistance, risk for pest outbreaks and environmental contamination; and decreased biological control through toxicity to natural enemies.

    Recent research conducted by this team and others has revealed the importance of farmscape-scale crop management, including nitrogen (N) application rates, crop rotation and alternate plant hosts (weeds and other crops) to management of onion thrips and IYSV. Building upon this knowledge base, we will 1) expand commercial onion field surveys to refine cultural management predictors of pests and yield; 2) develop an interactive tool linking changes in onion management practices to estimated profit and risk; 3) further define the response of thrips and IYSV to management of key weed hosts; 4) determine if high N rates suppress plant defense compounds and lead to increased thrips densities and greater risk for transmission of IYSV; and 5) develop outreach educational products including an instructional video for the online risk assessment tool; a comprehensive extension bulletin and companion video demonstrating key onion systems management practices to reduce pest pressure and optimize yield; presentations; slideshows; posters; and research and trade publications.

    Outreach efforts will assist the onion industry and support communities (research, Extension, State Department of Agriculture and Natural Resources Conservation Service) in better designing cropping landscapes, crop fertility programs and weed management strategies to minimize risk from thrips and IYSV. Onion farming is inherently a risky business. Access to a risk prediction model will empower producers to be pro-active in long-range planning, explore alternate crop rotation and management scenarios, and better evaluate the costs and benefits of their farming choices. The results will benefit society through greater farm sustainability and enhanced worker safety from reduced pesticide exposure. These benefits will strengthen onion farming communities and promote good stewardship of its natural resources.

    The 2012 Pest Management Strategic Plan for Dry Bulb Storage Onions in the U.S. (DeFrancesco 2012) identified weeds, thrips, IYSV and other pathogens as the highest priorities for research and education. A Western SARE needs assessment ranked longer-term, systems research and model farms demonstrating sustainable practices as top priorities in the Mountain Region. At a February 2012 Utah onion industry stakeholder roundtable, producers cited crop fertility management, thrips and IYSV control, and development of onion budgets as their top priorities. Our onion team includes leadership and participation from producers, researchers and educators. We are poised to make significant progress in understanding critical interrelationships among onion crop nutrition, field cultural practices, pest management, yield and profitability. Our results and outreach products will be especially relevant to onion production across the western U.S., as well as to other states and countries where onion thrips, IYSV and weeds are economically important pests.

    Project objectives from proposal:

    1. Collaborate with Utah onion producers in a survey of 60 commercial onion fields to expand and refine production system predictors of pests and yield (2013 and 2014).

    In a previous project funded by Western SARE (SW08-076), we surveyed 31 commercial onion fields to gather baseline data on which crop production parameters were most predictive of pest levels and yield (see Figure 1). We found strong positive correlations between total N applied and number of insecticide sprays and incidence of thrips and IYSV (more N and more sprays led to more pests). Both soil and onion tissue N were positively correlated with pest numbers but were not correlated with total yield and only marginally correlated with bulb size. The highest incidence of IYSV was in fields growing onions two years in a row. Additional parameters related to pest pressure and yield included soil organic matter, microbial activity and pH. We propose to expand our dataset to include more growing seasons and fields and add key landscape parameters such as identification of adjacent crops, onion cull piles and volunteer plants, and field-edge weed pressure. This expanded dataset will serve as the foundation for an interactive onion economic risk model to be developed in Objective 2. In addition, survey results will guide content of an outreach video to be developed in Objective 5.

    2. Develop a crop risk model based on onion production and pest management parameters associated with profitable yield and quality (2013-2015).

    The onion risk model will be an interactive Excel spreadsheet that will allow producers to examine the economic effects (profit and risk) of changes in production techniques. It will utilize a database developed from over 90 commercial onion field-year replicates. It will be easily accessible and free to use on the USU Extension website. The risk model will guide users in changing their production system practices to optimize external inputs such as fertilizer and pesticides, protect the environment and worker safety through reduced pesticide use, and optimize profits through targeting key yield goals (e.g., total weight, bulb size, bulb quality) which vary with market destination.

    3. Determine how management of key weed hosts influences incidence of onion thrips and IYSV in onion (2014 and 2015).

    We have documented that common mallow, prickly lettuce and field bindweed support thrips populations and test positive for IYSV in Utah onion landscapes. In a factorial design on an experimental farm, we will evaluate thrips and IYSV severity in onions adjacent to 1) monocultures of these three weeds, diverse weed mixtures, and weed-free plots; and 2) weeds suppressed (by mowing) or not before thrips populations peak in mid-summer. Results will guide weed management priorities within and near onion fields to reduce risk for pest colonization.

    4. Determine linkages between reduced N fertilization rate, onion tissue N, phenolic defense compounds and thrips populations (2013 and 2014).

    In experimental plots, we will confirm previous results that found a decreased fertilizer rate leads to reduced onion tissue N and thrips densities without compromising onion yield and with little effect on bulb size. These results will be used to further inform the development of a risk model (Objective 2) and provide a potential mechanism for lower pest pressure in reduced fertilized onion. We will determine the concentrations of common phenolic defense compounds and thrips densities in onion plants fertilized with high and low N rates. We anticipate that low N plants will have higher levels of defense compounds and lower densities of thrips. We will determine how N and phenolic levels influence thrips population structure, including motile adults and larvae, fecundity (eggs) and viability (egg hatch). Increased risk for acquisition and spread of IYSV is associated with onions on which thrips reproduction and viability is high because the virus is only acquired by immature thrips. A better understanding of how N levels and plant defense compounds influence thrips populations and IYSV infection will enhance our ability to design crop and pest management strategies with greater long-term sustainability.

    5. Develop and deliver outreach products to the onion industry and research, extension and regulatory communities of interest; and assess project impacts (2013-2015).

    Outreach educational products and activities will include the interactive crop risk tool and its instructional video, a crop management practices demonstration video, numerous presentations, field days, posters and publications in research, trade and Cooperative Extension outlets. The products will be easily accessible on the USU Extension website, linked to key national onion websites, such as Onion ipmPIPE, Onion Information Cooperative and Allium Net, and distributed at state, regional and national conferences.
    In addition to ensuring that useable knowledge generated in the project is disseminated to all relevant parties, we will thoroughly assess the impacts of the project through three major efforts: 1) grower roundtable each year to gather input and feedback on farm surveys, research experiments, crop risk model and outreach products; 2) written surveys to evaluate changes in grower behaviors and adoption of crop and pest management practices from the beginning to the end of the project; and 3) two online surveys for users of the crop risk model; one to gather feedback and improve the user interface, and one to assess changes in behavior and impacts.
    The comprehensive educational materials developed from this project will have significant impacts on Utah onion production, as well as the entire U.S. onion industry (over 1,750 and 76,000 acres planted in 2012, respectively, National Onion Association).

    Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.