Black spots on leaves

Overview

Black spots indicate active tissue necrosis. They need fast treatment because they can compromise the whole plant within weeks.

Common causes are bacteriosis (oily spots with yellow halo), anthracnose (target-like spots) and sunburn (crispy dry spots).

Differential diagnosis

Wet black spots with yellow halo → bacteriosis.

Concentric target-like spots → anthracnose.

Dry spots only on the sun-facing side → sunburn.

Natural remedies

Immediately remove and burn infected leaves — do not compost. Spray horsetail decoction every 5 days for 3 weeks.

Treatments

Copper fungicide (Bordeaux mixture) for anthracnose. Bacteriosis has no cure: isolate the plant and remove affected tissue.

Prevention

Avoid wetting foliage, ventilate.