Evaluation of Organic Soil Treatments for Managing Lettuce Fusarium Wilt Disease

Commodities

• Vegetables: greens (lettuces)

Practices

• Crop Production: biological inoculants, fertilizers, greenhouses
• Education and Training: demonstration, extension, networking, on-farm/ranch research
• Farm Business Management: budgets/cost and returns
• Natural Resources/Environment: biodiversity
• Pest Management: biological control, biorational pesticides, botanical pesticides, chemical control, competition, cultural control, field monitoring/scouting, integrated pest management, weather monitoring
• Production Systems: organic agriculture, transitioning to organic
• Soil Management: organic matter, soil analysis, soil microbiology, soil quality/health

Fusarium wilt of lettuce, caused by the soilborne fungus Fusarium oxysporum f. sp. lactucae (Fol), poses a significant threat to United States’ over $4 billion lettuce industry. This serious disease disrupts water and nutrient transport, causing wilting, stunting, and often plant death. Fol survives in soil for extended periods as chlamydospores, making eradication nearly impossible once fields are infested. Traditional management strategies, such as crop rotation, soil fumigation, and use of resistant cultivars, have had limited success due to the pathogen’s persistence and adaptability. Recent detection of highly virulent Fol variants capable of overcoming resistant cultivars demonstrates the urgent need for innovative sustainable management solutions.

This project evaluates the efficacy of organic treatments such as contact based oils, biological controls, and fertilizers, in suppressing Fusarium wilt and improving crop health. Greenhouse trials will screen several treatments for their effects on reducing disease severity and plant physiological health, with the most effective advancing to field trials conducted under commercial conditions. This dual-phase approach aims to provide growers with practical and research-backed recommendations while gaining insights into the relationship between disease suppression, and plant and soil health.

The project aligns with California’s Sustainable Pest Management Roadmap by identifying viable alternatives to synthetic fungicides and supporting soil health. Educational outreach will share findings to a large audience including growers, advisors, and researchers, and consumers through events, publications, and digital media, emphasizing the practicality of these treatments for managing soilborne diseases. By addressing critical gaps in Fusarium wilt management, this study contributes to sustainable agriculture by helping growers in navigating a growing market for natural based solutions, identifying effective tools to reduce disease impact, enhance soil and plant health, and improve economic viability. Its findings are relevant to both organic and conventional systems, with broader implications for managing soilborne diseases across diverse cropping systems.

Research Objectives

1. Evaluate the Efficacy of Organic Treatments for Fusarium Wilt Management

   • Conduct greenhouse trials to screen a variety of organic treatments, including biological-based  and fertilizer-based solutions, to assess their ability to reduce disease severity and improve plant health.
   • Validate the most promising treatments under field conditions at commercial lettuce farms to determine their real-world efficacy in managing Fusarium wilt.

2. Quantify Disease Suppression and Pathogen Reduction

   • Measure Fusarium pathogen populations in soil before and after treatment applications using selective plating methods on Komada’s medium.
   • Assess disease severity using standardized rating scales and correlate these with physiological plant health metrics, such as stomatal conductance and transpiration rate, measured using a Lycor 600 Porometer.

3. Identify Potential Synergies Between High-Sulfur Fertilizers and Biofungicides

   • Investigate the combined effects of high-sulfur organic fertilizers and Trichoderma-based biofungicides for enhanced suppression of Fusarium wilt.

4. Provide Growers with Field-Validated Data for Decision-Making

   • Generate robust, third-party validated efficacy data for organic treatments, bridging the gap between controlled and field conditions.
   • Develop practical recommendations for integrating these treatments into sustainable pest management strategies.

Educational Objectives

1. Disseminate Findings to Growers and Stakeholders

   • Host outreach events, including a field day at Cal Poly, to share results with growers and pest control advisors.
   • Present results at industry-focused events such field days and through platforms like the Grimm Organic Center podcast.

2. Engage Broader Audiences Through Publications

   • Publish research findings in academic journals (e.g., Plant Disease, American Phytopathological Society Journal).
   • Develop grower-focused articles for industry publications such as Progressive Crop Consultant.

3. Enhance Knowledge of Fusarium Wilt and Soil Health Interactions

   • Provide data-driven insights into the relationship between soil health and plant physiology under disease stress, contributing to broader discussions on sustainable agriculture practices.

4. Develop Educational Media for Sustainable Practices

   • Produce a video series summarizing research findings and practical applications of organic treatments to enhance accessibility and adoption among growers.