Sweet Onion Bacterial Disease Research and Grower Cooperator Farm Trials

Working Toward the Development of a Research-based Integrated Pest Management Program

Sweet onions are susceptible to several bacterial diseases that cause both bulb and leaf decay. Yield losses can be considerable both in the field and after harvest while in storage. In 2008, despite efforts to reduce losses by harvesting and drying down the crop early, Lancaster and Chester County growers culled up to an estimated 50 percent of the sweet onion crop as a result of bacterial diseases. Many of these onions were being growers for the Pennsylvania Simply Sweet Onion Program, Pennsylvania’s only trademarked crop. The total Pennsylvania sweet onion crop was valued at an estimated $1.5 million in 2008. Today there is a waiting list of growers interested in growing PA Simply Sweet Onions.

In collaboration with growers, Penn State Extension educators and an adult educator with the Eastern Lancaster School District, we have been using both traditional laboratory methods as well as modern DNA-based techniques to try to identify what bacterial pathogens are causing these yield losses and where they are coming from each season. We are looking at modifying the environment around the onion by using different types and colors of plastic mulch and plant spacing to make it less favorable for the pathogen to cause disease. We are evaluating alternative in-season management options that reduce grower reliance on copper-based bactericides. Results from these trials as well as product efficacy trials conducted on other crops such as pumpkin and tomato become the foundation of the Commercial Vegetable Production Guide, which is updated annually and available online at These trials are currently being conducted at the Southeast Research and Extension Center as well as the Russell E. Larson Research and Education Center and on collaborating grower farms.

By leveraging funding from the Pennsylvania Vegetable Growers Association and Pennsylvania Vegetable Research and Marketing Board, we received a grant from the Northeast Regional IPM program in 2011 in collaboration with researchers at Cornell to address these questions. Over the past two years we have established 90 onion survey plots on 30 growers-cooperator farms each year so we can better understand what factors contribute to bacterial diseases and develop integrated management strategies that are targeted and cost-effective. This will facilitate the production of higher quality onions and extend the seasonal marketability of sweet onions in Pennsylvania.

About the Researcher:
Beth Gugino is an assistant professor of vegetable pathology in the Department of Plant Pathology and Environmental Microbiology at Penn State. Her applied research and extension program focuses on the diagnosis, monitoring and forecasting of vegetable disease outbreaks to provide timely in-season information growers can use to make informed disease management decisions; development and evaluation of innovative, sustainable disease management strategies that can be cost-effectively incorporated into integrated pest management programs by growers and evaluation of the efficacy of conventional fungicides, biochemical and microbial biopesticides for in-season management of important and emerging disease of vegetable crops in Pennsylvania. 

Contact Information:


Phone:  814-880-8939