Epidemiology and management of fusarium basal rot in onions (VN20006)
What was it all about?
Challenges
Fusarium basal rot has emerged as a major concern in onion production areas, particularly in South Australia, causing bulb infections in the field and storage losses exceeding 30 per cent in some crops. Short crop rotations, high soil inoculum levels, and suboptimal soil moisture conditions exacerbate the disease, while latent infections often remain undetected until after harvest. The pathogen’s ability to infect a wide range of crops and weeds further complicates control efforts, while nitrogen and salinity management challenges increase disease susceptibility. Effective disease management requires innovative strategies, diagnostic precision, and improved understanding of Fusarium oxysporum f. sp. cepae (Foc) behaviour.
Response
The project developed an integrated pest and disease management (IPDM) approach, focusing on disease diagnostics, control measures, and predictive tools. This involved developing a new diagnostic tool, enhancing understanding of the pathogen, and evaluating various control methods, including chemical and biological options.
A review of existing literature provided a foundation for identifying factors conducive to infection and guiding management strategies. Field trials were conducted to assess the efficacy of treatments, with a focus on early intervention and integrated pest management practices.
The insights were consolidated into a grower-friendly guide, offering evidence-based strategies to minimise disease risk and improve productivity in onion production systems.
Benefit
This initiative equips the Australian onion industry with tools and knowledge to combat fusarium basal rot, reducing storage losses and enhancing yield quality. Improved diagnostic capabilities enable early detection, mitigating latent infections that could otherwise go unnoticed. By refining disease management practices, the project fosters sustainable production, protecting growers' investments and maintaining supply chain integrity.
The adoption of innovative control strategies and optimised resource management ensures long-term industry resilience, while the practical guide empowers growers and agronomists with actionable insights to safeguard onion crops and support the industry’s profitability.
ACT NOW
Read the Onion Fusarium Basal Rot guide June 2022 edition here.
To understand key drivers of disease development, crops were monitored in paddocks encompassing a range of rotation and production practices, soil moisture conditions and varieties. Incidence of bulb rot associated with Fusarium species ranged from nil to 55 per cent in monitored areas. Results from the first season of monitoring highlight the impact that high and prolonged soil moisture can have on increased incidence of bulb rots caused by Fusarium and bacterial infection. These findings are based on both monitoring soil moisture variation along the same planting lines within a crop, and measured differences in soil moisture between crops where inoculum of Fusarium oxysporum f. sp. cepae was known to be present. Testing of samples at the 5-7 leaf stage indicated that infection can already have occurred, though may not be visually evident until late in the crop or storage. Associations between reduced incidence of fusarium basal rot and nutrient levels have also been identified that will be further investigated.
Testing of mature bulbs with typical fusarium basal rot symptoms has confirmed they are primarily associated with the pathogen Fusarium oxysporum f. sp. cepae (FOC). The ability of the pathogen isolated from the onion bulbs to cause disease has been confirmed by controlled environment trials on onion seedlings. Cultures of this pathogen are being maintained to assist in the controlled environment evaluation of chemical and biological treatments aimed at reducing fusarium basal rot.
A specific DNA test has been developed for FOC. Testing of soil samples as part of the projects crop monitoring program covering high and low risk paddocks across two growing regions of South Australia has detected the pathogen in a small number of samples. To understand key drivers of disease development crops are being monitored in paddocks encompassing a range of rotation and production practices, soil moisture conditions and varieties.
This project is a strategic levy investment in the Hort Innovation Onion Fund