Round-leaf Calathea with Rust? Rare but Treatable
Calathea orbifolia
Rust is a common fungal disease caused by fungi in the order Pucciniales that affects a wide variety of plants. The disease gets its name from the characteristic orange, yellow, or reddish-brown pustules that appear on leaves, resembling metal rust. This obligate fungal parasite requires living plants to survive and can cause significant economic losses in agricultural crops.
ð Symptoms
- âĒ Raised orange, yellow, brown, or red pustules on leaf surfaces
- âĒ Ring-shaped or oval spore masses, typically on leaf undersides
- âĒ Premature yellowing and leaf drop
- âĒ Stunted plant growth
- âĒ Orange dust transferring to hands or clothing when touched
- âĒ In severe cases, death of entire leaves
â Possible Causes
- â Infection by lightweight fungal spores carried by wind or water
- â Wet foliage for 6-10 hours at temperatures of 15-25°C (59-77°F)
- â High humidity and poor air circulation
- â Late-day overhead watering leaving leaves wet overnight
- â Nearby alternate host plants (many rust fungi require two hosts)
- â Soft, susceptible growth due to excess nitrogen
ð Treatment
Quick Fixes
Immediate Pruning
Cut all visibly infected leaves and dispose. Clean tools.
Systemic Application
Apply systemic fungicide (azoxystrobin or similar) according to package instructions. Product will be absorbed and circulate through the plant.
Reapplication
Reapply after 7-14 days as per product label.
Environmental Adjustment
Switch watering to early morning and improve ventilation.
Organic Treatment
Mechanical Removal
Remove all infected leaves and parts with clean shears. Dispose in trash (not compost). Clean tools with 70% alcohol between cuts.
Sulfur Application
Apply sulfur fungicide to all leaf surfaces, especially undersides. Do this in the morning for quick drying. Do not apply above 30°C (86°F).
Watering Adjustment
Switch to drip irrigation or water directly at soil level. If using overhead watering, do so between 5-10 AM.
Improve Circulation
Prune dense branches to increase airflow. Maintain proper spacing between plants.
Monitoring
Inspect weekly. Reapply sulfur every 7-10 days for 3 weeks. Continue for 2 weeks after last symptom.
ðĄïļ Prevention
- â Water early morning (5-10 AM) to allow leaves to dry
- â Use drip irrigation instead of overhead sprinklers
- â Improve air circulation through proper pruning
- â Remove fallen leaf debris where spores can overwinter
- â Plant resistant cultivars when available
- â Avoid excessive nitrogen fertilization
- â Quarantine new plants for two weeks
- â Remove and destroy infected parts when infestation is minimal
- â Wash tools between plants to prevent spread
ðą Care Guide: Round-leaf Calathea
ð§ How to Water
Keep the substrate consistently moist but not waterlogged. Water approximately every 7 days in summer and every 10-14 days in winter. Use filtered or water left to sit for 24-48 hours to avoid mineral damage.
âïļ Lighting
Place in an area with medium to high indirect light, near a window but protected from direct sun. Avoid direct sunlight at all costs as it will burn the leaves.
ðŠī Ideal Soil
Requires acidic, well-draining substrate rich in organic matter. Porous composition helps prevent root rot while maintaining necessary moisture.