Fungal Severity: High ⚠️ Contagious

Pythium Root Rot: Urgent! How to Save Your Plant

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.

Spread speed

Fast

Recovery time

14 days

🔍 Symptoms

Main Symptoms

! Dark brown to black wet rot of roots
! Roots soften and disintegrate easily
! Outer cortical tissue pulls off easily exposing vascular strand
! Brown and dead root tips
! Stunted growth and undersized plants
! Wilting during the day with recovery at night
! Progressive yellowing of leaves
! Plant collapse and death in severe cases
! Crown may turn brown-black with soft rot

Visual Signs

Dark brown to black wet rot of rootsRoots soften and disintegrateOuter cortical tissue easily pulls off exposing vascular strandBrown to black lesions on root tipsStunted plant growthWilting at midday with recovery at nightYellowing and dying plantsCrown may also turn brown-black with soft rot

Affected parts: RootsStem

❓ Possible Causes

→ Infection by Pythium species (P. aphanidermatum, P. ultimum, P. irregulare)
→ Soil moisture above 70% of available water capacity
→ Poor drainage and waterlogged substrate
→ Overwatering or too frequent irrigation
→ Favorable temperatures (above 77°F for P. aphanidermatum, lower temperatures for other species)
→ Use of non-pasteurized or contaminated substrate
→ Contaminated pots, tools, and surfaces
→ Spread through contaminated irrigation water
→ Transmission by fungus gnats and shore flies
→ Excessive levels of ammonium or soluble salts in substrate

💊 Treatment

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Quick Fixes

~7 days

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Materials needed:

Cyazofamid (high-efficacy fungicide)Mefenoxam (Subdue MAXX) - check resistanceFluopicolide (alternative)Fresh sterilized substrateNew or disinfected potSterilized pruning scissorsProtective gloves

🌿

Organic Treatment

~14 days

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Materials needed:

3% hydrogen peroxideCinnamon extract or oilComposted pine barkGliocladium virens or Trichoderma (biocontrol)High-quality well-draining substrateSterilized pruning scissorsClean potDisinfectant solution (70% alcohol or diluted bleach)

🔬

Expert Treatment

~21 days

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Step by Step

1
IMMEDIATE: Stop all watering and let substrate dry
2
Remove plant from pot and carefully inspect roots
3
Cut all brown, soft, or rotting roots with sterilized scissors
4
Wash remaining roots with clean water
5
Treat roots with 3% hydrogen peroxide or appropriate fungicide
6
Repot in fresh, well-drained, sterilized substrate
7
Use clean, disinfected pot (wash with 10% bleach solution)
8
Water lightly only after repotting and keep substrate moist, not waterlogged
9
Improve drainage and permanently reduce watering frequency
10
Monitor daily for 2-3 weeks for signs of new infection
11
Apply preventive fungicide as recommended
12
Isolate treated plant from others to avoid cross-contamination

🧪 Solutions

🌱 Natural Solutions

✓ Steam substrate at 140°F for 30 minutes
✓ Use solarization with double-tent coverage (160°F for 30 min or 140°F for 1h)
✓ Add 20% composted pine bark to substrate
✓ Apply Gliocladium virens biocontrol agent to substrate
✓ Improve drainage and reduce watering frequency
✓ Use diluted hydrogen peroxide (3%) for rescue irrigation
✓ Apply cinnamon extract or neem oil as natural fungicide
✓ Remove and discard severely infected plants
✓ Isolate affected plants to prevent spread

💉 Chemical Solutions

✓ Mefenoxam (Subdue MAXX) - preventive or curative application
✓ Fluopicolide - high efficacy with low environmental impact
✓ Cyazofamid - only treatment effective for curative control in research
✓ Fenamidone - preventive control
✓ Boscalid + Pyraclostrobin - combination for broad control
✓ Etridiazole - preventive option
✓ Fosetyl-Al - systemic effect
✓ Propamocarb - substrate application
✓ IMPORTANT: Some Pythium strains are resistant to mefenoxam - rotate between fungicide classes