Amaryllis with Pythium Root Rot: Prevention & Cure
Hippeastrum vittatum
Pythium root rot is a serious fungal disease caused by various Pythium species including P. aphanidermatum, P. ultimum, and P. irregulare. These water molds are present in practically all cultivated soils and attack plant roots under wet conditions, causing rapid wet rot that can extend into the stem. The disease is favored by poor drainage, overwatering, and specific temperatures depending on the species.
ð Symptoms
- âĒ Dark brown to black wet rot of roots
- âĒ Roots soften and disintegrate easily
- âĒ Outer cortical tissue pulls off easily exposing vascular strand
- âĒ Brown and dead root tips
- âĒ Stunted growth and undersized plants
- âĒ Wilting during the day with recovery at night
- âĒ Progressive yellowing of leaves
- âĒ Plant collapse and death in severe cases
- âĒ Crown may turn brown-black with soft rot
â Possible Causes
- â Infection by Pythium species (P. aphanidermatum, P. ultimum, P. irregulare)
- â Soil moisture above 70% of available water capacity
- â Poor drainage and waterlogged substrate
- â Overwatering or too frequent irrigation
- â Favorable temperatures (above 77°F for P. aphanidermatum, lower temperatures for other species)
- â Use of non-pasteurized or contaminated substrate
- â Contaminated pots, tools, and surfaces
- â Spread through contaminated irrigation water
- â Transmission by fungus gnats and shore flies
- â Excessive levels of ammonium or soluble salts in substrate
ð Treatment
Quick Fixes
Step 1
Step 2
Step 3
Step 4
Step 5
Step 6
Organic Treatment
Step 1
Step 2
Step 3
Step 4
Step 5
Step 6
Step 7
ðĄïļ Prevention
- â Use well-drained substrate with adequate air pore space
- â Pasteurize or solarize substrate before use (140°F for 30 min)
- â Avoid overwatering and maintain good water management
- â Ensure proper drainage in pots and beds
- â Inspect roots of new plant material before introducing to collection
- â Keep pots, tools, and growing areas clean and disinfected
- â Keep irrigation hose ends elevated off the ground
- â Avoid excessive levels of ammonium and soluble salts in substrate
- â Use substrate with at least 20% composted pine bark
- â Control fungus gnats that can transmit spores
ðą Care Guide: Amaryllis
ð§ How to Water
Water 2-3 times per week during flowering and active growth. Completely stop watering when leaves wilt to allow the necessary dormancy period. Avoid wetting the bulb directly to prevent rot.
âïļ Lighting
Prefers bright indirect light. Can tolerate morning sun but protect from intense midday sun. Rotate the pot occasionally for even growth.
ðŠī Ideal Soil
Use well-draining substrate composed of equal parts peat, soil, and sand. Plant the bulb leaving 1/3 exposed above the soil. Avoid waterlogging which can rot the bulb.