What are these yellow patches on my white mustard leaves?

Check these first

1. Check the underside of the yellowed leaves for fuzzy growth.
2. Observe if the spots are angular or irregular in shape.
3. Feel the soil to see if it has been staying too wet.

Likely causes

1. Downy mildew

   Most likely

   How to tell: You will see yellow, angular spots on the upper leaf surface and a fuzzy, grayish growth on the underside. It spreads quickly in damp weather.

   What to do: Remove and destroy the infected leaves immediately to stop the spread. Improve air circulation by thinning out your plants and avoid overhead watering.

2. Nutrient deficiency

   Possible

   How to tell: The yellowing is usually more uniform across the leaf rather than in distinct patches or spots. It often starts on the older, lower leaves first.

   What to do: Apply a balanced liquid fertilizer diluted to half strength every 2 weeks. Ensure your soil is rich in organic matter before planting.

When to worry

Downy mildew can kill a plant if left unchecked, so treat it as soon as you spot the first yellow patch. Normal aging of the lowest, oldest leaves is expected as the plant grows.

Stopping it coming back

Water at the base of the plant rather than over the leaves to keep foliage dry. Space your plants 6 to 10 inches apart to ensure good airflow.

Questions people ask

Can I save a plant with downy mildew?

If you catch it early and remove the infected parts, you can often save the plant. If the whole plant is covered, it is best to remove it to protect your other greens.

Does this fungus live in the soil?

Yes, it can survive in plant debris, so always clean up your garden beds at the end of the season.

More problems with White Mustard

• Why are there tiny holes in my white mustard leaves?
• Why is my white mustard growing so tall and thin?