White Mold is caused by the soil-borne fungus Sclerotinia sclerotiorum. It survives for years in soil as hard black structures called sclerotia. Under cool, moist conditions these can produce spores that infect susceptible plant tissue, particularly where foliage remains damp. Infection often begins as a soft, water-soaked area on stems, leaves or heads, followed by the characteristic white cottony fungal growth. As the disease progresses, affected tissue rots and black sclerotia develop within or on the mouldy tissue. Dense plantings, prolonged wet weather and poor airflow favour disease.

How to Fix It
Remove infected plants: Remove affected plants promptly, including any visible black sclerotia, and dispose of them rather than composting them.
Improve airflow: Space plants adequately and control weeds so foliage dries more quickly.
Keep foliage dry: Water at soil level and avoid unnecessary overhead watering.
Improve drainage: Avoid persistently wet soil and poorly drained planting areas.
Rotate crops: Rotate away from susceptible vegetables where practical, although the fungus has such a broad host range that rotation alone is not particularly effective.
Clean up crop debris: Remove infected plant material after harvest, especially tissue containing sclerotia.
Avoid spreading contaminated soil: Clean soil from tools and equipment before moving between affected and unaffected garden areas.