Water rot

Pythium debaryanum, Pythium ultimum and Pythium splendens

Symptoms

• Brown sunken spots on damaged tuber surface
• Disease spreads rapidly towards the centre of the tuber
• Sliced tubers turn black. Some species will first show a light pink discolouration
• Dark border around the infected tuber tissue, clearly visible through the skin
• Tuber tissue becomes creamy and finally liquid
• Tubers can leak enormously, causing wet rot
• In the later stages only an empty skin is remaining

Infection and spread

• Naturally found in soils
• Fungus only infects damaged tubers
• Usually occurs in wet, hot seasons
• Harvesting in hot conditions and full sun increases the risk of infection

Possible confusion with

• Wet rot
• First symptoms of late blight (Phytophthora infestans)
• Pink rot (Phytophthora erythroseptica)