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Potato Pink Rot

Potato Pink Rot

George Little and Louise Cooke
Applied Plant Science and Biometrics Division
The wet summer and recent flood damage to some potato crops may result in tubers with pink rot sometimes referred to as ‘water slain’.  This disease occurs sporadically on heavy, moisture-retentive soils, but conditions this year may encourage infection more widely.  The causal agent of pink rot is the soil-borne pathogen Phytophthora erythroseptica and it is one of the most damaging tuber diseases as apparently healthy tubers at harvest can deteriorate within a few weeks of being placed into store.

Symptoms

The disease usually starts at the stolon end with affected skin becoming discoloured and darkened around the lenticels; the margin of decay may be visible through the tuber skin as a dark line and a vinegary odour can sometimes be detected, especially in potato stores containing affected tubers.  Pink rotted tubers are rubbery, exude juice when squeezed and on cutting, the diseased area changes colour from cream to salmon pink within 20 to 30 minutes and then to black in approximately one hour.

Disease cycle

The disease can survive for many years in soils in the form of oospores.  These can initiate infection when the soil approaches saturation as a result of poor drainage or heavy rain.  Tubers are usually infected through stolons, eyes or damage points and all underground plant parts are susceptible.  During harvesting operations, box filling and store loading, diseased tubers can infect healthy potato tubers.

Control measures

  • Check for infected tubers in poorly drained or previously flooded parts of fields by test digging and cutting any suspect tubers.
  • If infected tubers are found take particular care during harvesting and subsequent handling to minimise damage and to remove any affected tubers before storage.
  • Tubers from fields with significant pink rot levels should be harvested and kept separate for immediate grading, marketing or disposal.
  • Ventilate boxes and bulk store piles to help mummify diseased tubers and reduce development of pockets of soft rot.
  • Allow at least a 5 year rotation to help reduce carry-over in soil and avoid fields with a history of pink rot.