Leaf Blight

Symptoms by part

Causes

• Prolonged periods of high humidity
• Poor air circulation around the foliage
• Frequent overhead watering that keeps leaves wet
• Temperatures that remain consistently warm and damp

Could be confused with

• Nutrient deficiency · Deficiencies usually show uniform yellowing or patterns across the whole plant, whereas blight appears as localized, irregular dead spots.
• Sunscald · Sunscald typically affects leaves exposed directly to intense light and does not spread to shaded parts of the plant like a disease does.

Treatment

1. Prune away all affected leaves using sterilized shears to stop the spread.
2. Dispose of all removed plant material in the trash rather than the compost pile.
3. Increase spacing between plants to improve airflow and allow foliage to dry faster.

Without chemicals

• Remove and destroy fallen leaves from the soil surface.
• Switch to base watering to keep foliage dry.
• Use a rain cover or move container plants to a sheltered area during wet weather.

Chemical options

• Potassium bicarbonate, mix with water and spray on foliage to alter the pH and inhibit fungal growth, follow the label.
• Sulfur, apply as a dust or spray to prevent further fungal spore germination, follow the label.

Preventing it

• Water only at the base of the plant to keep leaves dry.
• Ensure adequate spacing between plants for better air movement.
• Clean up all plant debris at the end of the season to remove overwintering spores.
• Choose varieties known for better disease resistance.

When to act

Act as soon as you notice the first spots to prevent the infection from covering the entire plant. If more than half of the plant is affected and it fails to recover after pruning, remove and replace the plant entirely.

Questions people ask

Can I compost the leaves I pruned off?

No, it is best to throw them in the trash. Most home compost piles do not get hot enough to kill the pathogens, and you risk spreading the disease back to your garden next year.

Will my plant die from leaf blight?

It depends on how early you catch it. If you remove the infected parts and improve the growing conditions, most plants will recover, but severe cases can cause enough stress to kill the plant.