Raker Trials 2024 – Cut Flowers | Brian Sparks
The following article is part of the APS Outreach Project, an initiative of the American Phytopathological Society:
For cut flower growers committed to cost-effective and resilient practices, soilborne diseases are a significant barrier, impacting crop health and threatening profitability. While some research has explored the application of Anaerobic Soil Disinfestation (ASD) in ornamental plants, these efforts remain limited compared to its demonstrated success in vegetable farming. As ASD gains traction as an efficient and economically viable approach to managing soilborne diseases in vegetables, there is an urgent need to expand research into its effectiveness for cut flower production. A deeper understanding of ASD’s potential could reshape disease management strategies for flower growers, enabling them to protect their crops without relying on high-cost chemical inputs.
The Soilborne Disease Problem in Cut Flower Production
Soilborne pathogens such as Fusarium, Phytophthora, and Rhizoctonia thrive in the natural soil found in high-tunnel and field-grown flower farm operations, causing root rot, stem cankers, and wilt. These pathogens persist in soil, making it challenging to manage outbreaks with traditional chemical fumigants, which are not only costly but can also have long-term impacts on soil quality.
Due to the importance of aesthetics in cut flowers, disease can greatly impact production and the amount of saleable product. Soilborne diseases can result in 50-75% crop loss in certain species, according to the Handbook of Florists’ Crops Diseases. In 2022, the USDA reported $333 million in sales in the cut flower industry, which means dealing with disease can cost growers, and the industry, significantly. For growers adopting lower-cost and more stable production practices, the options are even more limited, as chemical fumigants are either restricted or undesirable. As flower farming intensifies in areas where soilborne pathogens are prevalent, cost-effective, reliable soil management practices are essential.
Anaerobic Soil Disinfestation: An Economically Viable Solution?
Anaerobic Soil Disinfestation is an innovative approach to managing soilborne pathogens that has shown promise in vegetable production. The process involves creating an oxygen-depleted environment by incorporating a carbon source (such as rice bran or molasses) into the soil, followed by saturating the soil with water and covering it with a plastic tarp. As the organic material decomposes in these anaerobic conditions, it produces by-products toxic to many soilborne pathogens.
Studies have shown that ASD can effectively reduce the incidence of soilborne diseases by more than 80% in certain vegetable crops, according to research published in the Plant Pathology Journal. In a controlled study, ASD reduced Verticillium wilt by 90% in tomato crops, demonstrating its potential as an alternative to traditional fumigants. Given these successes, extending ASD trials to cut flowers could offer a breakthrough in soilborne disease management in this industry and help flower growers reduce costs associated with chemical treatments.
Challenges and Limitations: The Need for Further Research
While ASD holds promise, more research is required to better understand its efficacy in cut flower production. A large portion of the research on ASD’s effectiveness has been conducted in vegetable crops, leaving critical knowledge gaps when it comes to flowers – but there have been a handful of studies that focus on them. ASD has currently been proven successful in controlling Fusarium wilt of carnation in Argentina, Verticillium wilt on lilies in the Netherlands, root-knot nematode on cut flowers in Florida, and Rhizoctonia stem rot on zinnia in Ohio. Flower crops differ significantly from vegetables in root structure, growth habits, and soil needs, which may impact how ASD affects both pathogens and the plants themselves. Additionally, implementing ASD on a commercial scale in flower beds presents logistical challenges. The process requires considerable preparation time, specific organic amendments, and thorough soil saturation – factors that may be more complex in flower farms with diverse crop rotations and varying soil structures.
ASD’s efficacy is impacted not only by the soil type and carbon source used but also by the temperature of the area it is conducted in. Temperature can impact the survival and activity of organisms in the soil, altering the by-products that are toxic to pathogens. Only two studies have been conducted on cut flowers in temperate regions; investigating how ASD compares in different climates is key in producing well-rounded grower guidelines. To make ASD a feasible option, researchers must test its impact on the pathogens common in flower farming and explore the climatic conditions under which it is useful.
Use Case #1: Control of Rhizoctonia Stem Rot in Zinnia
At The Ohio State University, researchers investigated ASD as an avenue for controlling Rhizoctonia stem rot in zinnia in a controlled greenhouse environment. When tested as carbon amendments for ASD, wheat bran and tomato pomace reduced Rhizoctonia disease incidence by 67-92% compared to the control. An additional experiment, conducted in outdoor raised beds, showed reduced disease severity in plots treated with wheat bran. These experiments confirm that ASD is a suitable disease management option for Rhizoctonia stem rot management in cut flower production.
Control of Phytophthora root rot on gerbera daisy was also evaluated in the initial experiment but proved to be more of a challenge for ASD: the amendments tested did not significantly control disease incidence or severity. However, due to the broad range of possible carbon amendments, and the influence of soil texture on the success of ASD, there is hope yet that ASD – conducted under the right conditions – could be a management option for oomycete root rots. These findings underscore the message that ASD can’t be done with a one-size-fits-all approach and must be tested in the most pressing flower-disease systems to confirm its efficacy.
Use Case #2: On-Farm Trials in Cut Flower Production
In North Carolina, a few forward-thinking flower growers have collaborated with researchers on preliminary ASD trials. These growers reported improvements in crop resilience, reduced disease incidence, and lower management costs. However, the effectiveness of ASD varied depending on flower species, soil conditions, and the types of pathogens present. One grower observed a significant reduction in root rot among zinnias and sunflowers but found limited impact on more susceptible plants like dahlias.
These trials highlight the variability in ASD’s success across different flower types and underscore the need for tailored ASD applications that consider flower-pathogen interactions and soil preferences. For ASD to be a viable solution for the cut flower industry, further trials are essential to develop optimized practices and identify economically compatible flower varieties.
Next Steps: Creating a Framework for ASD in Cut Flower Production
To enable cut flower growers to adopt ASD as a viable soilborne disease management strategy, the following actions are recommended:
Expand Research Funding for ASD in Flowers:
More funding is necessary to conduct ASD trials specific to flower production. Grants could support collaborative efforts between universities and growers to conduct on-farm trials, studying ASD’s effects on pathogens in different flower species, soil types, and climatic regions.
Develop Best Practices and Resources:
To ensure growers can apply ASD effectively, extension services and industry bodies should work together to produce guidelines that detail what combination of organic matter, duration of treatment, and average temperature results in effective disease control for various flowers and their diseases. Educational materials that detail the economic benefits and practical risks of ASD for specific flower types would empower growers to make informed decisions.
Promote Grower-Researcher Partnerships:
On-farm research is essential to bridge the gap between academic studies and practical applications. Partnerships with growers who are already engaged in resilient and cost-efficient practices would facilitate ASD trials in real-world settings, offering insights into the financial viability and long-term impacts on soil health.
Create an ASD Certification Program:
To support adoption, an ASD certification could signal that flowers are grown using reliable and economically sound practices, adding market value for growers who choose this method. Certifications could also set standardized ASD practices for different regions, soil types, and flower species.
Moving Toward Economic Sustainability in Disease Management
With soilborne diseases threatening the economic resilience of cut flower farming, ASD represents a promising alternative to costly chemical fumigants. However, to unlock its full potential, further research and field trials are essential to adapt this technique to the unique demands of flower production. By investing in ASD research, creating grower resources, and establishing industry standards, the flower industry can move closer to a financially sustainable approach to soilborne disease management.
ASD is one tool that growers can implement for disease management as part of a larger integrated pest management program. The success of ASD in vegetable production provides a strong foundation, but realizing its benefits for cut flowers requires a collaborative, economically focused effort among researchers, growers, and industry leaders. With the right support and resources, ASD could become a vital tool for flower growers committed to profitable and resilient practices, ensuring their fields stay productive and financially viable.
