Aphid monitoring in Scotland
Summary
Leaf roll levels increased in the 2023 crop, and although PVY levels stabilised they remained relatively high. However, the activity of M. persicae and species of aphids known to transmit viruses were at or below average, so although virus inoculum in Scottish crops is currently higher than average this could decrease slightly in 2024.
The warmer than average temperatures over 2023-24 winter indicate that aphid activity should be 2-3 weeks earlier than average this season. Consequently, population levels have the potential to develop to levels that could threaten the virus health of seed crops.
Therefore effective management of the source of inoculum, increased vigilance of the timing and number of aphids in your area, and a balanced approach to the management of both leaf roll and non-persistent viruses is important, with attention paid to varietal susceptibility and the development of aphid populations as the season progresses.
The 'six-step recommendations for effective virus management in seed potatoes', developed by Scottish Aphid-borne Virus Working Group members provides excellent practical advice for protecting crops.
Aphid monitoring tools
Aphid monitoring is an important tool to help inform growers on the risk of virus transmission to and within crops. There are three main methods of aphid monitoring, all are important in assessing risk –
Suction traps provide information on aphid migrations and first flights. These are important to monitor ‘seeding events’ when aphids are likely to enter a crop, and are useful for both leafroll and mosaic causing viruses. Four suction traps are located in Scotland, representing aphid activity over a radius of around 80km. Aphids will normally only fly at the height of suction traps once in their lifetime (their first flight) so this informs us when they move to new hosts, or when risk factors, such as high population within a crop or a high predator load, drive populations to move to a new host. The latest aphid bulletins using suction traps are available here and predicted aphid vector pressure (for PVY) is here.
Yellow pan traps provide information on localised aphid movement, as they find a suitable host. They are important to monitor ‘hot spots’ where population numbers are building in an area and may move to new crops. Pan trap data are useful for both leafroll and mosaic causing viruses. A network of pan traps with good coverage across seed growing areas is optimal to monitor the level of localised movement and rapidly pick up where hot spots are developing. An update of the latest from the aphid monitoring network (using pan traps managed by FERA) is available here.
In-field aphid monitoring carried out by inspectors was introduced into the SPCS in 1992 to encourage growers to control aphids developing on their crops. This was effective at encouraging the management of the potato colonising aphids that transmit leaf roll, but was not as successful in assisting with the control of the non-colonising aphids that transmit non-persistent viruses. Whilst active in-field monitoring by inspectors is not carried out in every crop they will take action if populations are discovered during inspection. In-field monitoring remains an important tool to inform management of aphids which can spread leafroll, and growers should remain vigilant to the build up of aphid populations in their own crops.
SASA