Fungi are among the main enemies of ornamental plants, especially in indoor environments where poor ventilation and excessive humidity can create favorable conditions for their development. These diseases often go unnoticed until they cause visible symptoms such as spots, leaf drop, and even root rot. In this article, you’ll learn how to recognize the main fungal diseases that affect houseplants, how to treat them, and how to prevent future outbreaks.
1. Powdery Mildew
Description: Appears as a white, powdery coating on leaves, stems, or flowers. It’s common in warm, humid environments with poor air circulation.
Symptoms:
- White or grayish powder on the upper side of the leaf.
- Leaf distortion and yellowing.
- Premature leaf drop.
Treatment:
- Remove and discard affected leaves.
- Improve air circulation around the plant.
- Apply sulfur-based or potassium bicarbonate fungicides.
- Use homemade sprays such as milk (1 part milk to 9 parts water).
2. Leaf Spot (Cercospora, Septoria, Alternaria)
Description: Caused by different fungi that create brown, yellow, or black spots on leaves, often with defined borders.
Symptoms:
- Circular or irregular dark spots.
- Yellowing of the surrounding area.
- Early leaf fall in more severe cases.
Treatment:
- Remove affected leaves.
- Spray with copper-based or organic fungicides (e.g., neem oil).
- Avoid wetting the leaves during watering.
3. Root and Stem Rot (Pythium, Rhizoctonia, Fusarium)
Description: One of the most serious fungal problems, often associated with waterlogged soil and poor drainage.
Symptoms:
- Wilting even when the soil is moist.
- Bad smell from the roots.
- Dark and mushy roots.
- Yellowing and stem base rotting.
Treatment:
- Remove the plant from the pot and trim off affected roots.
- Repot using new, well-draining soil.
- Apply biological fungicides (Trichoderma spp.) or cinnamon powder on the roots.
- Avoid watering until the substrate dries slightly.
4. Botrytis (Gray Mold)
Description: Common in high humidity, it affects leaves, flowers, and stems with gray, fluffy mold.
Symptoms:
- Brown, soft spots on leaves and flowers.
- Rapid decay of flower buds.
- Appearance of a gray, fuzzy layer.
Treatment:
- Remove all affected parts.
- Reduce air humidity and avoid misting.
- Improve ventilation.
- Use fungicides containing iprodione or copper.
5. Anthracnose
Description: A disease caused by fungi such as Colletotrichum, it causes necrotic spots and sunken lesions on leaves and stems.
Symptoms:
- Brown or black spots with defined edges.
- Leaf tips dry and die.
- Lesions may spread to stems.
Treatment:
- Remove infected leaves.
- Spray with copper-based or sulfur fungicides.
- Avoid excess moisture on the foliage.
Prevention: The best cure
Preventing fungal problems is easier than treating them. Here are key tips:
- Ensure good ventilation in the environment.
- Use well-draining substrates (especially for succulents and orchids).
- Avoid excessive watering.
- Don’t mist plants excessively, especially in humid climates.
- Water in the morning, so leaves dry during the day.
- Sterilize tools and pots before use.
Homemade antifungal recipes
- Cinnamon tea:
- Boil 1 tbsp of cinnamon powder in 1 liter of water.
- Let cool and spray on the plant.
- Baking soda solution:
- 1 tsp baking soda + 1 drop of liquid soap + 1 liter of water.
- Spray once a week to prevent fungi.
- Horsetail infusion (rich in silica):
- Acts as a strengthening and antifungal agent.
- Boil horsetail in water, let it cool, strain, and spray.
Plant recovery
After treating fungal diseases, it’s important to help the plant regain health:
- Remove infected parts carefully.
- Avoid fertilizing immediately after treatment.
- Let the plant rest in a bright, ventilated area.
- Resume fertilization gradually after about two weeks, using balanced or organic fertilizers.
Specific cases
- Peace Lily with brown spots: Could indicate leaf spot or botrytis. Remove the affected leaves and reduce humidity.
- Succulents with rot at the base: Likely root rot. Cut off the healthy part, let it dry, and try to replant in dry soil.
- Orchids with leaf spots: Often caused by fungi or bacteria. Improve air circulation and apply sulfur or cinnamon.
When to discard a plant?
If more than 70% of the plant is compromised, with rot spreading to the main stem or roots, it may be better to dispose of it to avoid spreading to others. In these cases, burn or discard the plant in a sealed bag and disinfect all tools and surfaces that came into contact with it.
Fungal diseases are part of the challenges of growing ornamental plants but can be controlled with the right information and good habits. Observing the plant frequently, adjusting watering, and providing the right environment are the keys to a healthy, fungus-free indoor garden. With prevention and proper treatment, your plants can recover and thrive again.