Summary & Outlook
Inspection of the 2017 Scottish seed potato crop revealed an incidence of crops containing virus affected plants of 4.8% of the total area entered for classification (down from 6.7% in 2016). This is the lowest level of virus incidence recorded since the instigation of the Scottish seed Potato Classification Scheme.
The incidence of mosaic symptoms (i.e. excluding leaf roll) decreased to 4.5% from 6.4% in 2016. Within this 4.5%, the incidence of PVY was recorded at 3.6%, precisely the level that we predicted in March 2017. Unfortunately without the Elgin trap operating in 2017 a revised model, based on catches from just the Dundee and Edinburgh suction traps, using the three most abundant cereal aphids which have been most closely linked with PVY transmission in Scotland, provides a retrospective prediction of 4.0%. This same model is predicting that PVY will decrease from 3.6% of the SPCS crop area containing plants with symptoms to 2.8% in 2018. The incidence of crops containing any leaf roll decreased from 0.26% in 2016 to 0.25% in 2017. The model based on aphid data before the introduction of aphid monitoring in 1992 predicted an increase in leaf roll to around 0.7-0.8% of the crop area for 2017.
Following the 2017-18 winter, when temperatures were slightly below average, the SASA forecasts for the first suction trap catches of peach-potato aphids are 21 June for Edinburgh and 23 June for Dundee, some 6 weeks later than in 2017. Following moderate activity of this species in 2017, a slight increase in the level of leaf roll (to 0.7%) is expected for the 2018 crop. Following record low levels of virus in 2017, the 2018 crop is predicted to contain even less virus.