Aphid Monitoring of Seed Potato Crops

Aphid monitoring, which was introduced into the SPCS in 1992 to encourage growers to control aphids developing on their crops, has proved effective at encouraging the management of the potato colonising aphids that transmit leaf roll.  It has not proved as successful in assisting with the control of the non-colonising aphids that transmit non-persistent viruses.  Although leaf roll levels increased during 2018 and higher than average activity of M. persicae is predicted for 2019, the risk of further transmission is not considered to be sufficiently high to merit the reintroduction of aphid monitoring during 2019 crop inspections.  A balanced approach to the management of both leaf roll and non-persistent viruses is required for 2019, with attention paid to varietal susceptibility and the development of aphid populations as the season progresses. 

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 2019.  The model based on aphid data before the introduction of aphid monitoring in 1992 predicted an increase in leaf roll to around 0.7% of the crop area for 2018.  As a result of above average temperatures during winter 2018-19 winter, the SASA forecasts for the first suction trap catches of peach-potato aphids are 1 June for Edinburgh and 9 June at Dundee, around 1 to 3 weeks earlier than in 2018. Following moderately high activity of this species 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 Myzus persicae activity was high in 2018 and to 4.5% based on data from Edinburgh where Myzus persicae activity was relatively lower in 2018.