Optimizing Cropping and Soil Systems for Integrated Management of Lettuce Fusarium Wilt

Commodities

• Vegetables: greens (leafy), greens (lettuces)

Practices

• Crop Production: crop rotation, plant breeding and genetics, varieties and cultivars
• Education and Training: decision support system, on-farm/ranch research
• Pest Management: cultural control, weather monitoring

Fusarium wilt, caused by the fungal pathogen Fusarium oxysporum f. sp. lactucae (Fol), is a major soilborne disease that threatens lettuce production in California. In infested fields, producers may experience up to 70% yield reduction or, in severe cases, total crop loss. Because the pathogen can survive in soil for more than 10 years and effective chemical control options are limited, management of Fusarium wilt remains a significant challenge for lettuce producers. This project aims to develop integrated and sustainable strategies to help growers manage the disease while maintaining profitability through three objectives: (1) to support lettuce growers in selecting appropriate varieties through a comprehensive evaluation of Fusarium-tolerant lettuce varieties; (2) to develop a bioassay to support growers in making informed decisions on lettuce variety selection and planting timing; and (3) to evaluate reductions in Fusarium infestation levels following the cultivation of non-host or resistant varieties. We will conduct field trials, collect and analyze soil samples, and work directly with growers in affected production regions. The project will help producers understand how widely the pathogen is distributed, how persistent the pathogen is in the soil, and why complete eradication is unlikely. Instead, our goal is to provide tools that allow growers to produce lettuce successfully in the presence of Fol while minimizing management costs and slowing down pathogen buildup in production fields. With the knowledge generated from this study, growers will be able to conduct a simple bioassay to estimate Fusarium infestation levels before planting in their fields. This information will help them make informed decisions about variety selection and management strategies. Growers will learn when and where it is necessary to plant Fusarium-tolerant varieties and under what conditions these varieties should be combined with additional management practices. By using this approach, growers can reduce unnecessary seed costs and increase the likelihood that tolerant varieties will perform successfully in fields with higher Fusarium infestation levels.

Findings will be disseminated through field days demonstrations, presentations at extension meetings, workshops, handouts, social media, research and trade journals, and bilingual outreach materials to ensure accessibility across the agricultural community and academia. In addition, the project will provide hands-on research training for Cal Poly students, helping prepare the next generation of agricultural professionals in sustainable plant disease management. Through close collaboration with lettuce producers, this study will deliver science-based and economically feasible solutions to support long-term lettuce production in Fusarium-infested soils.

Project research objectives:

(1) To support lettuce growers in selecting appropriate varieties through a comprehensive evaluation of Fusarium-tolerant lettuce varieties.

(2) To develop a bioassay to support growers in making informed decisions on lettuce variety selection and planting timing.

(3) To evaluate reductions in Fusarium infestation levels following the cultivation of non-host or resistant varieties.

Education Objectives:

(1) Growers will understand that Fusarium-tolerant varieties are not completely resistant to Fusarium wilt.
(2) Growers will become familiar with at least five common lettuce diseases that affect marketability of lettuce and will be able to compare varietal horticultural traits.

(3) Growers will understand key abiotic and biotic factors influencing Fusarium wilt development.
(4) Growers will learn how to use a bioassay to estimate Fusarium infestation levels in their fields.

(5) Growers will understand that rotating away from lettuce (the host) can reduce Fusarium inoculum levels in soil.
(6) Growers will recognize that Fusarium-tolerant varieties may still become infected and contribute to pathogen buildup.

(7) To teach students about soilborne diseases and the sustainable management of these diseases in agricultural systems.