Pythium Leak (Water Rot)

HOSTS

• Potatoes

DESCRIPTION

Pythium leak, caused by Pythium ultimum, affects potatoes in storage and in the field. 

BIOLOGY

P. ultimum survives in soil and on crop debris, and thrives in areas with high soil moisture. The pathogen invades potato hosts through pre-existing wounds, and less commonly, through the lenticels. Symptoms of leak can develop rapidly when the temperature is 75 °F or higher, causing the potato to discharge a clear or brownish liquid. Tubers may also develop “shell rot” when the internal tissue rots, leaving only the dry, papery skin. 

Symptoms of pythium leak are usually seen at harvest or during storage. The spread of P. ultimum in storage is limited, however, secondary infections easily spread to the susceptible tubers. 

SYMPTOMS

• Water-soaked lesions. 
• Brown or gray decaying tissue with a spongy texture. 
• Clear to brown discharge when the tuber is squeezed. 
• Sour odor. 
• Tubers with internal tissue rotted out leaving the skin as a dry shell. 

GENERAL MANAGEMENT

• Handle tubers carefully, especially during harvest, to minimize tuber injuries. 
• Minimize excess soil moisture by avoiding overwatering and ensuring soils are well-draining. 
• Harvest potatoes when conditions are cool (below 75 °F) and dry. 
• Maintain cool and dry conditions for potatoes in storage.