Phytophthora

What is it?

Phytophthora species are oomycetes — not true fungi — that thrive in saturated soils and wet canopies. Different species attack roots, crowns, stems, foliage and fruit. They produce swimming spores that move in water, making wet conditions the key driver.

How to identify it

• Wilting despite moist or wet soil; plants that don't recover after irrigation.
• Dark, rotting roots and reddish-brown crown or collar lesions.
• Water-soaked foliar or fruit lesions that expand rapidly in wet weather.
• Rapid plant collapse, often starting in low-lying or poorly drained areas.

Life cycle & spread

Survives in soil and infected debris as resting spores; produces swimming zoospores in free water that infect roots and splash onto foliage/fruit. Cycles rapidly under warm, wet conditions.

Conditions that favour it

Saturated soils, poor drainage, overwatering, and prolonged canopy wetness. Low spots and compacted soils are hotspots.

Damage and how it spreads

Kills roots and crowns (plant death), and rots foliage and fruit. Can move from a few plants to a whole block quickly in wet weather.

Monitoring & scouting

Watch low/wet areas and recently irrigated blocks; check roots and crowns of wilting plants; act preventively when wet conditions are forecast.

How to control it

1. Improve drainage and airflow, avoid overwatering, and apply protectant programs preventively.
2. Because oomycete infections can't be reversed once established, the goal is protecting healthy tissue and supporting plant defense.

Preventing it next season

Site drainage, irrigation management, resistant rootstocks where available, and preventive application ahead of wet periods.

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