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ARS Home » Pacific West Area » Salinas, California » Crop Improvement and Protection Research » Research » Publications at this Location » Publication #424891
Research Project: Disease Management and Improved Detection Systems for Control of Pathogens of Vegetables and Strawberries

Location: Crop Improvement and Protection Research

Title: Downy mildew epidemiology and spinach seed treatment

Author
item Klosterman, Steven

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 3/25/2025
Publication Date: 3/25/2025
Citation: Klosterman, S.J. 2025. Downy mildew epidemiology and spinach seed treatment. California Leafy Greens Research Program Annual Meeting, March 25, 2025, Pismo Beach, California.

Interpretive Summary:

Technical Abstract: Seedborne Verticillium dahliae causes Verticillium wilt in mature spinach and can cause wilt of a broad range of rotational crops, including lettuce (Lactuca sativa), strawberry (Fragaria x ananassa), and others. Peronospora effusa exclusively infects spinach, causing destructive downy mildew. Managing these pathogens is highly challenging, creating a need for effective seed disinfection methods. We examined two different fumigant seed treatments, nitrogen dioxide (NO2) and sulfur dioxide (SO2) to limit the spread of V. dahliae and P. effusa in spinach seeds. NO2 fumigation (3% NO2 for three days) significantly reduced both external and internal V. dahliae by 60.7% to 91.0% and eliminated P. effusa from spinach seeds. Notably, NO2 fumigation enhanced seed germination and plant growth. In contrast, SO2 fumigation (0.25 - 0.5% for one hour) had a significant negative impact on seed germination, reducing the germination by 7.0% to 16.4% and did not reduce pathogen viability substantially. These findings highlight NO2 fumigation as an effective approach for controlling V. dahliae and P. effusa in spinach seeds. Additional work is ongoing to monitor the diurnal pattern of airborne spore dispersal of P. effusa and Bremia lactucae, the latter of which causes downy mildew on lettuce. The early research results indicate higher levels of dispersal in the early afternoon ours, and this is correlated with increased wind speeds. Knowledge gained from the studies examing airborne pathogen dispersal can help to reduce fungicide sprays, or allow them to be optimally timed.