Late blight

Phytophthora infestans

Symptoms

• Initial infection: blue spots slightly visible through the skin
• Sunken, dark, lead grey, hard spots on the tuber surface
• Rust brown coloured tissue inside the tubers, somewhat filamentous
• Fungal growth is possible in humid conditions
• Often develops in the presence of other types of rot

Infection

• During the growing season, during harvesting and storage
• Infection through zoospores via lenticels, eyes or damage
• Infiltration of zoospores into the soil via water

Spread

• Survives in infested tubers (as mycelium)
• Relative humidity and temperature determines spread
• Survives in soil as zoospores (short lived) and oospores (long lived)
• Infection possible at all stages of the growing season
• Can also spread and develop during harvest and storage