Downy Mildew on Herbs and Vegetables: Identify, Treat & Prevent the Spread

If your plant’s leaves suddenly develop yellow spots and then brown, fuzzy patches underneath, you're likely facing a fungal disease known as downy mildew. It spreads quickly and can destroy herbs like basil and parsley within days if left untreated.

Here’s how to detect it early and stop it in its tracks.

What Is Downy Mildew?

Downy mildew is caused by water-loving pathogens (oomycetes) that thrive in humid, poorly ventilated environments. It infects the leaves first, especially in the early morning when foliage is wet.

Commonly affected plants include:

• Basil

• Parsley

• Mint

• Cucumbers

• Squash

• Grapevines

Symptoms of Downy Mildew

• Pale yellow spots on top of the leaves

• Gray, fuzzy growth underneath the spots

• Leaf curling, browning, or early drop

• Affected leaves feel thin or soft

• Rapid plant decline in wet conditions

It often starts at the bottom of the plant and moves upward.

How to Treat Downy Mildew

1. Remove Affected Leaves Immediately
   Cut and discard any infected foliage—do not compost it.

2. Improve Airflow
   Space your plants properly, trim dense growth, and avoid overcrowding.

3. Water Early and Avoid Wetting Leaves
   Always water at soil level and do it in the morning.

4. Use Organic Fungicides
   Spray with copper-based fungicides or a homemade solution of baking soda and mild soap (1 tsp baking soda + 1 qt water + 1 drop dish soap).

5. Apply Neem Oil Preventively
   While it doesn’t kill mildew directly, it helps prevent further spread.

Long-Term Prevention Tips

• Choose resistant plant varieties when possible

• Avoid watering at night

• Remove garden debris regularly

• Rotate crops if you grow in soil beds

• Ensure good drainage and reduce humidity indoors