Summary & Outlook

Inspection of the 2016 Scottish seed potato crop revealed an incidence of crops containing virus affected plants of 6.7% of the total area entered for classification (down from 7.0% in 2015).  This is the lowest level recorded since 2003 (5.2%). 

Changes to the classification scheme mean that the incidence of severe mosaic symptoms is no longer recorded at inspection, all mosaics being classed together.  The incidence of mosaic symptoms decreased to 6.4% from 6.7% in 2015. 

The incidence of PVY was recorded at 5.1%, markedly above the level of 2.4% predicted in March 2015.  Using the same model, based on the three most abundant cereal aphids which have been most closely linked with PVY transmission in Scotland, the incidence of PVY is expected to decrease from 5.1% of the SPCS crop area containing plants with symptoms to 3.6% in 2017.  The incidence of crops containing any leaf roll decreased from 0.35% in 2015 to 0.26%.  In 2017, leaf roll is expected to increase to around 0.7-0.8% of the crop area.

Following the 2016-17 winter, when temperatures were above average, the SASA forecasts for the first suction trap catches of peach-potato aphids are 22 May for Edinburgh and 29 May for Dundee.  Following a similar early forecast in 2016, the potential for populations of this species to build up to significant levels during the period of crop growth did not materialise, so minimal levels of leaf roll are expected when the 2017 crop is grown.