Moon Orchid with Phytophthora Blight? Rare but Treatable
Phalaenopsis amabilis
Devastating fungal disease caused by Phytophthora species (primarily P. capsici and P. infestans), famously responsible for the Irish Potato Famine in the 1840s. Affects all plant parts including roots, stems, leaves, and fruits in warm, wet conditions. The pathogen is technically an oomycete (water mold) that thrives in saturated soils and can survive in soil for 5+ years.
ð Symptoms
- âĒ Water-soaked lesions on leaves with vague borders and white fluffy fungal growth
- âĒ White powdered sugar-like spores on infected tissue
- âĒ Grey-brown centers with light-green edges on leaves
- âĒ Black, water-soaked roots and crown
- âĒ Elongated brown lesions on stems that encircle the stem
- âĒ Wilting plants that pull easily from soil
- âĒ Soft, water-soaked rot on fruit
- âĒ Bluish lesions on tubers
- âĒ Buckeye rot on tomatoes with concentric target-like pattern
â Possible Causes
- â Warm (75-85°F / 23-29°C) and wet conditions with high soil moisture
- â Free water essential - zoospores swim through water films
- â Saturated, poorly drained soils where water puddles
- â Excessive or overhead irrigation
- â Pathogen overwinters in soil and plant debris for 5+ years
- â Spread via water, wind, rain, and contaminated soil on equipment
- â Presence of oospores (survival structures) in soil
ð Treatment
Quick Fixes
Immediately apply systemic fungicide (mefenoxam) as soil drench
Spray foliage with phosphonate or fosetyl-Al
Remove visibly infected plants within 24 hours
Cease all irrigation for 3-5 days to dry soil
Repeat fungicide applications every 5-7 days for 3 weeks
Implement drainage system or raised beds
Organic Treatment
Remove and dispose of all infected plants plus 2 feet of neighboring plants
Improve drainage with raised beds 8-12 inches high
Apply copper-based fungicide to remaining plants every 7-10 days
Reduce irrigation frequency and use drip irrigation only
Incorporate well-cured compost into soil for beneficial microbiome
Monitor daily and immediately remove any new infection
ðĄïļ Prevention
- â Plant in well-drained areas using raised beds
- â Avoid working in wet, compacted soils
- â Rotate for minimum 3 years out of susceptible crops
- â Use well water rather than surface water for irrigation
- â Clean equipment thoroughly to remove soil
- â Scout low-lying areas where water accumulates
- â Choose resistant cultivars when available
- â Ensure adequate air circulation for rapid drying
- â Avoid over-irrigation and overhead watering
- â Disinfect recirculating nutrient solutions
ðą Care Guide: Moon Orchid
ð§ How to Water
Water thoroughly when the potting medium is nearly dry, typically every 7-10 days. Use room temperature water and avoid letting the plant sit in standing water. Reduce watering in winter.
âïļ Lighting
Place in bright, indirect light - an east or west-facing window is ideal. Avoid direct sunlight which can burn the leaves. In winter, supplemental artificial light can encourage blooming.
ðŠī Ideal Soil
Use a well-draining orchid mix consisting of bark chips, perlite, and sphagnum moss. The pH should be slightly acidic (5.5-6.5). Never use regular potting soil as it retains too much moisture.