Summary & Outlook
Inspection of the 2018 Scottish seed potato crop revealed an incidence of crops containing virus affected plants of 9.4% of the total area entered for classification (up from 4.8% in 2017).
The incidence of mosaic symptoms (i.e. excluding leaf roll) increased to 7.3% from 4.5% in 2017. Within this 7.3%, the incidence of PVY was recorded as having increased from 3.6% to 6.9%, contrary to the decline to 2.8% that we predicted in March 2018. Without the Elgin trap operating in 2017 and 2018 we are relying on 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, to provide a prediction of 8.0% in 2019.
The incidence of crops containing any leaf roll increased from 0.25% in 2017 to 3.1% in 2018. This exceeded predictions based on models using data from both Dundee and Edinburgh suction traps. Following moderately high activity of Myzus persicae in 2018, a further increase in the level of leaf roll to 6.5% is expected for the 2019 crop based on data from Dundee where the activity of this species was high in 2018 and to 4.5% based on data from Edinburgh where Myzus persicae activity was relatively lower in 2018.