1. Introduction to African Violet Leaf Health
African violets (Saintpaulia spp.) are popular houseplants known for their vibrant flowers and velvety leaves. However, brown spots on their leaves can indicate underlying issues affecting their health. From a plant's perspective, these spots are often a response to environmental stress, pests, or diseases. Understanding the causes helps in maintaining optimal growing conditions.
2. Water-Related Issues
African violets are sensitive to water quality and watering practices. Brown spots may appear due to:
- Cold Water Shock: Watering with cold water can cause cell damage, leading to brown spots. The plant prefers lukewarm water to avoid thermal stress.
- Overwatering or Poor Drainage: Soggy soil suffocates roots, causing root rot. This disrupts nutrient uptake, leading to leaf discoloration and brown spots.
- Water on Leaves: Droplets left on leaves can act as magnifying glasses under light, causing localized burns (brown spots).
3. Light Stress
Light plays a critical role in leaf health. Brown spots may result from:
- Direct Sunlight: Intense light scorches leaves, causing brown patches. African violets thrive in bright, indirect light.
- Insufficient Light: Weak light weakens the plant, making leaves prone to discoloration and spotting.
4. Nutrient Imbalances
Nutrient deficiencies or excesses can manifest as brown spots:
- Excess Fertilizer: Salt buildup from over-fertilization burns roots and leaves, causing brown edges or spots.
- Calcium Deficiency: Poor calcium uptake (often due to irregular watering) leads to necrotic spots on leaves.
5. Pest Infestations
Pests damage leaves directly or introduce pathogens:
- Spider Mites: These tiny pests suck sap, leaving stippled brown spots.
- Mealybugs: Their feeding causes yellowing and browning, often near leaf veins.
6. Fungal and Bacterial Infections
Pathogens can invade leaves, causing brown spots:
- Leaf Spot Diseases: Fungi like Cercospora create circular brown spots with yellow halos.
- Bacterial Blight: Bacteria (e.g., Pseudomonas) cause water-soaked spots that turn brown and crispy.
7. Physical Damage
Mechanical injuries can lead to browning:
- Handling: Rough touching or pruning with unclean tools can wound leaves, inviting infections.
- Abrasion: Rubbing against nearby objects may scrape the leaf surface, causing brown marks.
8. Humidity and Temperature Fluctuations
African violets prefer stable conditions:
- Low Humidity: Dry air dehydrates leaves, leading to brown edges or spots.
- Temperature Extremes: Sudden drops or spikes stress the plant, manifesting as brown lesions.
9. Chemical Exposure
Harsh chemicals can harm leaves:
- Pesticides or Cleaners: Spray drift or residue may burn leaves, causing brown spots.
- Tap Water Chemicals: Chlorine or fluoride in water can accumulate in leaves, triggering browning.
