Unlocking the Code: The Strategy of White Mold Biocontrol for Organic Lettuce Production

Commodities

• Vegetables: greens (lettuces)

Practices

• Education and Training: on-farm/ranch research
• Pest Management: biological control
• Production Systems: organic agriculture

White mold (Sclerotinia sclerotiorum and S. minor) is the most devastating disease in organic lettuce operations across the Northeast, causing losses exceeding 50% in severely affected fields. Current organic management strategies focus on foliar protection using plant extracts (e.g., Regalia, Timorex ACT) or Bacillus species (e.g., Serenade, Stargus, Cease) to protect leaves from infection. However, this approach misses a critical piece of the white mold puzzle in leafy greens.

Preliminary data from PI Dr. Heck show that the secret lies beneath the soil surface: white mold in leafy greens begins primarily with myceliogenic germination of soilborne sclerotia that directly colonize plant tissues, rather than through airborne ascospores infecting flowers or leaves, as in several other crops (Heck et al., in preparation). While growers protect the canopy, the real battle occurs in the soil where sclerotia accumulate season after season, building inoculum loads that overwhelm foliar defenses.

This two-year partnership project will crack the code of effective white mold biocontrol by targeting the source, soil inoculum reduction. Working with two established organic farms, Sang Lee Farms and Garden of Eve, we will evaluate Actinovate (Streptomyces lydicus), LALSTOP Contans (Coniothyrium minitans), and BotryStop (Ulocladium oudemansii) applied at planting and at harvest in high-tunnel lettuce production during the fall seasons of 2026 and 2027.

Our research will determine optimal biocontrol product selection through disease assessment and sclerotia quantification. We will assess disease incidence and severity, and collect soil at transplanting (baseline), harvest, and two months post-harvest over two seasons. Using soil extraction and laboratory germination testing, we will measure how different products affect sclerotia density and viability, providing evidence of biocontrol efficacy at the inoculum source.

This research addresses a critical knowledge gap that prevents the widespread adoption of soil-focused biocontrol in organic systems. Current organic management lacks precision in selecting biocontrol products, leading to inconsistent results and skepticism. By evaluating which products provide the greatest inoculum suppression, we will provide organic lettuce growers with science-based protocols that target the source of infection.

Results will be disseminated through winter meetings, extension publications, and one peer-reviewed article. A practical product selection guide will translate research results into actionable soil-focused management recommendations for organic lettuce operations throughout the Northeast.

By unlocking the secrets of soil inoculum suppression, this project will transform white mold management in organic leafy greens production, shifting the focus from reactive canopy protection to proactive inoculum reduction in the soil.

1. Quantify white mold disease suppression achieved through soil-targeted biocontrol applications versus untreated controls.
Measure disease incidence and severity in lettuce crops treated with each biocontrol product compared to untreated controls through standardized biweekly assessments during fall production seasons 2026 and 2027.
2. Evaluate the comparative efficacy of three OMRI-listed biocontrol products for soil inoculum reduction in organic lettuce production systems.
Compare the effectiveness of Actinovate (Streptomyces lydicus), LALSTOP Contans (Coniothyrium minitans), and BotryStop (Ulocladium oudemansii) applied at planting and at harvest for reducing sclerotia density and viability in high-tunnel lettuce production across two growing seasons.
3. Determine optimal biocontrol product selection criteria based on inoculum suppression performance and disease control consistency.
Analyze sclerotia density reduction, viability suppression, and disease control data to identify which biocontrol products provide the most reliable and substantial soil inoculum reduction under realistic commercial organic production conditions.
4. Develop science-based product selection guidelines for organic lettuce growers implementing soil-focused white mold management strategies.
Translate comparative efficacy data into practical recommendations that enable organic producers to select biocontrol products based on expected performance, addressing the critical knowledge gap that currently limits biocontrol adoption.

This research addresses the critical question facing organic growers:

• Which biocontrol products provide the greatest reduction in white mold disease when applied at planting and at harvest in high-tunnel lettuce production?
• How do soil sclerotia density and viability differ among biocontrol treatments across multiple growing seasons?
• What product characteristics and performance metrics should guide organic grower selection among available biocontrol options?

This study provides the first direct comparative evaluation of leading OMRI-listed products under simultaneous commercial conditions in the Northeast, filling a knowledge gap that currently prevents widespread adoption of soil-targeted biocontrol strategies in organic lettuce production.