Golden Shower Orchid with Black Spot? Rare but Treatable
Oncidium varicosum
Black spot is the most serious fungal disease affecting roses, caused by the fungus Diplocarpon rosae. It is characterized by dark circular spots on leaves that progress to yellowing and premature leaf drop. The disease thrives in humid and cool conditions, especially early in the growing season.
ð Symptoms
- âĒ Purplish or black circular spots (up to 1/2 inch diameter) on upper leaf surface
- âĒ Irregular feathery borders on spots
- âĒ Yellow halo developing around spots
- âĒ Progressive yellowing of leaves starting from plant base
- âĒ Premature leaf drop
- âĒ Small black scabby lesions on young stems
- âĒ Nearly complete defoliation in severe cases
- âĒ Leaves show no symptoms on undersides
â Possible Causes
- â Infection by fungus Diplocarpon rosae
- â Leaves remaining wet for more than 7 consecutive hours
- â Humid and cool conditions in early spring
- â Poor air circulation around plants
- â Inadequate plant spacing
- â Evening or late irrigation keeping leaves wet
- â Spores overwintering on fallen leaves and infected canes
- â Spore dispersal through rain or overhead irrigation
ð Treatment
Quick Fixes
Remove all visibly infected leaves
Immediately
Apply systemic fungicide (penconazole or flutriafol)
Same day
Remove fallen leaves and debris from area
Daily for 3 days
Reapply fungicide
7 days after first application
Adjust irrigation to morning only
Immediately
Third fungicide application
14 days after first application
Organic Treatment
Remove and destroy all infected and fallen leaves
Immediately upon detection
Prune stems with lesions to healthy tissue
During dormancy or immediately
Apply diluted neem oil (follow manufacturer instructions)
Every 7-14 days, starting in early spring
Spray potassium bicarbonate solution on leaves
Every 7-14 days, alternating with neem
Apply sulfur powder on dry days
When temperature is below 80°F
Adjust irrigation to morning hours only
Daily
Apply mulch around plants
Early spring
ðĄïļ Prevention
- â Remove and destroy all fallen leaves in autumn or bury under mulch layers
- â Remove remaining leaves from plants during winter when possible
- â Prune out stem lesions before spring leaf emergence
- â Water in the morning so leaves dry quickly
- â Use drip irrigation instead of overhead sprinklers to keep foliage dry
- â Improve air circulation through proper spacing and regular pruning
- â Plant roses in locations with at least 6-8 hours of full sun
- â Avoid plant overcrowding
- â Disinfect pruning shears after each use
- â Choose disease-resistant cultivars
ðą Care Guide: Golden Shower Orchid
ð§ How to Water
Water when the substrate feels dry to the touch, usually 2-3 times per week in summer and once weekly in winter. Preferably water in the late afternoon. Ensure water drains completely, avoiding accumulation.
âïļ Lighting
Appreciates bright indirect light, preferably a few hours of morning sun. Avoid direct sun during the hottest hours. Dark green, soft leaves indicate insufficient light.
ðŠī Ideal Soil
Use substrate specific for epiphytes: 40% sphagnum moss, 30% charcoal, and 30% ground pine bark. The substrate must be very well-draining to prevent root rot.