Late season water management in potatoes and its impact on bruising and skinset



Previous observations of late season water management had shown that short term hydration, soil moisture deficit (SMD) and timing of mechanical defoliation can affect the potential for bruising. These observations indicate that better recommendations on water management close to defoliation should help in the prevention of bruising. In combination with N management, water plays a large role in governing the timing and rate of canopy senescence, which in turn is closely linked to the rate of skinset. Better information on management of water is crucial to enable rapid skinset, early harvest and reduction in blemishing diseases such as black dot and silver scurf. The aims of the project were to establish the extent to which late season irrigation management affects blackspot bruising and skinset in crops.


Over three seasons (2011, 2012 and 2013), tubers from six experimental and 50 commercial crops were impacted using a falling bolt to determine the sensitivity to bruising and a rumble barrel was used to assess the skinset of tubers from the detailed experiments.  The experimental crops had two irrigation regimes imposed (rainfed and irrigated to maintain SMDs below the limit for yield), whilst the commercial crops had their irrigation scheduled by the CUF Potato Irrigation Scheduling Model, with the end of season irrigation management being determined by the growers.  Six random areas were sampled within each commercial field and tubers impacted within 24 hours of harvesting.

Key Findings

In 4 out of 6 detailed experiments assessing the effect of late-season irrigation on bruising, there was a reduction in bruising incidence where SMDs were maintained below the limiting SMD for yield in the 3 weeks prior to desiccation compared with allowing the SMDs to increase to 20-30 mm above the limiting SMD.  Rainfall interceded in two of the experiments, so that a relatively small differential resulted between rainfed and irrigated treatments and there was no effect on bruising.

In commercial crops, there was no overall relationship between blackspot bruising incidence and any measure of SMD (mean, maximum, accumulated or stress SMD) during the 3-week period prior to desiccation or 50 % canopy senescence.  When grouping the data by variety, there was again no relationship between bruising and SMD in most varieties.  However, in Markies there was a significant increase in bruising as the SMD maintained prior to harvest increased.

In all detailed experiments, late-season irrigation management had no effect on skin-set.


In controlled experiments, it has proved possible to reduce bruising by maintaining moderate SMD’s close to desiccation or crop death when compared to rainfed crops.  This should be the target for growers during August rather than switching off irrigation and allowing the crop to survive on soil reserves alone in dry periods.  The concerns that maintaining small SMDs in the lead up to harvest will delay skinset have little scientific grounding and growers should concentrate on monitoring SMDs later in the season and irrigating where necessary.  The crucial objective is maintaining moderate, rather than low SMDs, since the latter can adversely affect other aspects of tuber quality (e.g. rotting diseases, dry matter and lenticel eruption) and soil conditions for harvest.

Project code:
04 January 2011 - 01 March 2014
Project leader:
Mark Stalham


R445 Late Season Water Management FINAL