Stop the Rot

Stop the Rot

Combating Onion Bacterial Diseases with Pathogenomics Tools and Enhanced Management Strategies

Onion bulb crops are grown on approximately 140,000 acres/year in seven primary regions of the U.S., with a farm-gate value of $925M. Bacterial diseases of onion cause more than $60M in losses annually to this industry. Losses can be particularly severe for stored bulbs as bacterial rots typically develop in storage, after all production costs have been incurred.

This ‘Stop the Rot’ project organizes 24 scientists in diverse disciplines across the U.S. to research the complete system (host, pathogen, environment) of bacterial diseases of onion. The aim is to develop practical, economically sound strategies for pathogen detection and management that will improve profitability and sustainability of onion production.

The project has two primary research objectives:

A:  National survey across all onion growing regions, so that we can compare the genomics of onion bacterial pathogens collected in different regions to:

  • identify virulence factors
  • develop practical molecular diagnostic tools for identifying specific bacterial pathogens
  • develop phenotypic resistance screening methods

B:  Through research trials, identify onion production practices, environmental factors and inoculum sources that impact bacterial diseases, then use this knowledge to develop effective, practical solutions for managing bacterial diseases.

This work is supported by Specialty Crops Research Initiative Award 2019-51181-30013 from the USDA National Institute of Food and Agriculture. 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.

“How Do We Stop the Rot?” new extension video from Washington State University provides an overview of bacterial diseases of onion and information on management of factors causing disease, as well as more about the Stop the Rot project. The video was shot in the Columbia Basin, but contains plenty of information relevant for onion production in other regions too.

“Battling Onion Bacterial Diseases with Bactericides”. A new article in the December 2020 issue of Onion World Magazine covers the results of trials conducted in Washington State to examine the efficacy of a number of different bactericides for the control of bacterial leaf blight and bulb rot in onion. A similar field trial was conducted in Pennsylvania. Both trials were funded by the Interregional (IR-4) Minor Crops Pest Program.

A new extension bulletin Bacterial Diseases of Onions in Georgia

Two new extension videos on basics of bacterial rots have been produced by co-PI Christy Hoepting and her Cornell team.

English   Spanish

Plant Disease Management Reports on Stop the Rot trials

Stop the Rot researchers recently published several new Plant Disease Management Reports on the results of field trials in the first season of work. Reports are now available from three participating states (GA, WA, NY).

Click Here to see the most current version of the Plant Disease Management Reports list.

Collated summaries of Year 1 Technical Reports: The Stop the Rot project team prepared a series of brief technical reports to cover the work conducted in Year 1 of the project for each research objective. The executive summaries of these 12 reports have been collated into a single document here. We hope this will provide a helpful overview of the Year 1 program of work and preliminary results

Seven primary regions of onion production in the U.S., including acres (A) of production (data from USDA NASS 2016; National Onion Association; onion stakeholders), predominant type of onion production, and current knowledge of onion bacterial pathogens that appear to be prevalent in each region (Bc = Burkholderia cepacia, Bg = Burkholderia gladioli pv. alliicola, Ec = Enterobacter cloacae and related species, Pag = Pantoea agglomerans, Pan = Pantoea ananatis, Pv = Pseudomonas viridiflava, Xaa = Xanthomonas axonopodis pv. allii). Acronyms of institutions involved in this project are shown in each state: CSU = Colorado State University, Cornell = Cornell University, MSU = Michigan State University, NMSU = New Mexico State University, OSU = Oregon State University, PSU = The Pennsylvania State University, TAM = Texas A&M University, UGA = University of Georgia, UI = University of Idaho, USU = Utah State University, UCR = University of California (UC) Agriculture & Natural Resources and UC-Riverside, WSU = Washington State University. *acreages on map are based on 2017 data

Bacterial diseases of onion occur across the U.S. They are difficult to manage due to a lack of effective, rapid detection methods, relatively poor understanding of the diversity and epidemiology of bacterial pathogens, and a lack of systemic bactericides that can treat these diseases and mitigate losses to the industry. In addition, there are few or no known resistant commercial cultivars.

We know from research and trials that a number of factors favor the development of bacterial diseases. These factors include:

  • Contaminated seed and transplants
  • Storm damage, rain, hail, frost damage
  • Mechanical wounds, insects (thrips), weeds
  • Irrigation – runoff, excess, overhead irrigation
  • Excessive fertility, especially post-bulb initiation
  • Moderate to high temperatures (>30oC), except for some Pseudomonas (cool to warm)
  • Dense plant stands
  • Some topping, curing, and handling practices
  • Insect pests – maggot, thrips
  • Weeds – symptomatic & asymptomatic hosts