Downy Mildew

The name downy mildew includes a wide variety of "water molds" that act as plant pathogens. Damage to plants often shows as leaf spots, blights and/or distortions. This is of primary concern in ornamental plant cultivation, but affects many edible crops including kale, mint and other low-lying varieties. Symptoms commonly show as grayish, fuzzy growth on lower leaves; however, there is significant variance from species to species and among different cultivars of the same crop. Sanitation and continued prevention efforts are essential when managing downy mildew outbreaks.

Downy Mildew Management:

Clean Up/Spot Treat – Sanitation is the first step to controlling downy mildews. Remove infected material and reduce overwintering sites by disposing of leaf litter and treating currently affected areas. This is the best first step to take if downy mildew is a concern.

  • OxiDate uses hydrogen peroxide to sterilize treated foliage & soil.
  • Neem oil can be used for spot treatment and smaller scale applications to foliage.
Limit Water Buildup – Downy mildew zoospores spread by swimming in free water on plant surfaces. Consider watering in late afternoon/evening to limit moisture during the cool morning period.

  • If drainage or overly wet conditions are a concern, consider using a biofungicide like Regalia or BONIDE Revitalize to help suppress existing downy mildew.
Chemical Fungicides – ZeroTol is a peroxide-based cleaner useful in killing overwintering mycelia and oospores. It can be used throughout the growing season, but will not cure affected plants. Thyme Guard has also shown promising results controlling and suppressing mildews.