Fungal Severity: High ⚠️ Contagious

Phytophthora Blight: Urgent! How to Save Your Plant

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.

Spread speed

Fast

Recovery time

14 days

🔍 Symptoms

Main Symptoms

! Water-soaked lesions on leaves with vague borders and white fluffy fungal growth
! White powdered sugar-like spores on infected tissue
! Grey-brown centers with light-green edges on leaves
! Black, water-soaked roots and crown
! Elongated brown lesions on stems that encircle the stem
! Wilting plants that pull easily from soil
! Soft, water-soaked rot on fruit
! Bluish lesions on tubers
! Buckeye rot on tomatoes with concentric target-like pattern

Visual Signs

Water-soaked lesions on leaves with vague bordersWhite fluffy fungal growth (powdered sugar-like spores)Grey-brown centers with light-green edges on leavesBlack, water-soaked roots and crownElongated brown lesions on stemsWilting plants that pull easily from soilSoft, water-soaked rot on fruitBluish lesions on tubersBuckeye rot on tomatoes (concentric target-like pattern)

Affected parts: LEAVESStemRootsFruitsWhole plant

❓ Possible Causes

→ Warm (75-85°F / 23-29°C) and wet conditions with high soil moisture
→ Free water essential - zoospores swim through water films
→ Saturated, poorly drained soils where water puddles
→ Excessive or overhead irrigation
→ Pathogen overwinters in soil and plant debris for 5+ years
→ Spread via water, wind, rain, and contaminated soil on equipment
→ Presence of oospores (survival structures) in soil

💊 Treatment

⚡

Quick Fixes

~7 days

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

Materials needed:

Mefenoxam fungicidePhosphonate foliar spraySprayerDrainage materials

🌿

Organic Treatment

~14 days

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

Materials needed:

Copper-based fungicideRaised beds or soilCured compostDrip irrigation system

🔬

Expert Treatment

~21 days

Test soil for Phytophthora presence and species identification

Remove infected zone with 3-foot borders, till deeply

Install tile drainage system or create permanent raised beds

Apply rotational fungicide program: phenylamide + phosphonate + copper

Implement subsurface drip irrigation with soil moisture sensors

Incorporate compost inoculated with Trichoderma and Bacillus

Establish sanitation protocol: equipment cleaning + footbath

Transition to resistant cultivars next season

Monitor with serological test kits weekly

Document disease patterns and treatment efficacy for adjustments

Step by Step

1
Immediately remove infected and neighboring plants
2
Dispose of diseased material away from production areas
3
Improve drainage before replanting
4
Apply preventive fungicides to remaining plants
5
Monitor daily for new infections
6
Avoid working in wet conditions
7
Implement 3-year crop rotation
8
Do not harvest or mix fruit from infested areas

🧪 Solutions

🌱 Natural Solutions

✓ Remove infected plants plus neighboring apparently healthy plants
✓ Improve drainage with raised beds and slope
✓ Apply strict hygiene measures
✓ Optimize plant potential and resilience
✓ Use longer intervals between irrigations
✓ Apply well-cured compost to boost beneficial microorganisms
✓ Implement tile drainage systems in fields

💉 Chemical Solutions

✓ Copper-based fungicides for preventive protection
✓ Phosphonates for root and foliar uptake
✓ Phenylamides (mefenoxam, metalaxyl) for root rot - apply to soil
✓ Contact fungicides containing aluminum tris or fosetyl-Al
✓ Multiple preventive applications throughout season
✓ NOTE: Resistance to mefenoxam and metalaxyl has been documented

🛡️ Prevention

✓ Plant in well-drained areas using raised beds
✓ Avoid working in wet, compacted soils
✓ Rotate for minimum 3 years out of susceptible crops
✓ Use well water rather than surface water for irrigation
✓ Clean equipment thoroughly to remove soil
✓ Scout low-lying areas where water accumulates
✓ Choose resistant cultivars when available
✓ Ensure adequate air circulation for rapid drying
✓ Avoid over-irrigation and overhead watering
✓ Disinfect recirculating nutrient solutions

🌿 Common in These Plants

Crimson Cattleya

Dumb Cane

Taro

African Milk Tree

Heartleaf Philodendron

Moon Orchid