Virus yellows is a disease 'complex' that involves a number of different aphid-transmitted viruses including the poleroviruses Beet mild yellowing virus (BMYV) and Beet chlorosis virus (BCh V), and the closterovirus Beet yellows virus (BYV) (Stevens et al., 2005). These viruses can decrease yields by up to 49% and in addition, virus infection increases impurity levels within the roots which impair sugar extraction at the processing plants. The UK's maritime climate favours the winter survival of the aphids which carry and spread the disease. Research shows that, in the absence of adequate crop protection, 8 of the last 12 years would have resulted in virus yellows epidemics which would have proved devastating to the industry. It is expected that climate change will exacerbate the problem by increasing winter survival of aphids, leading to earlier and larger flights into crops, more rapid build up of populations and more in-crop movement of aphids and hence spread of virus. The timing of crop planting is not expected to advance as fast as aphid flight activity and thus aphids will arrive in crops at an increasingly early growth stage when the crops are more susceptible to virus yellows infection.
The evolution of resistance in the main vector species, the peach-potato aphid Myzus persicae, to most insecticide groups, together with legislative restrictions, has lead to the industry becoming heavily reliant on neonicotinoid seed treatments for aphid control. Neonicotinoids have proven effective for many years, but resistance to neonicotinoid insecticides has recently been reported in M persicae in southern Europe, and it is likely that similar resistance will develop in, or spread to, the UK. The development of a robust management toolkit to help the industry overcome the threat this poses is seen as essential if the industry is to survive. This must comprise a complementary range of innovative technologies including development of resistant varieties, field testing of new insecticidal compounds, development of diagnostic, monitoring and forecasting techniques to ensure optimal use of insecticides, combined with integrated and timely dissemination of advice to growers.
Currently, around 120,000 units of sugar beet seed are bought and sown by UK growers and in 2014, approximately 96% of the seed was treated with neonicotinoid insecticides. If neonicotinoids fail due to insecticide resistance or are lost due to future EU legislation, the potential yield loss of up to 50% would render the industry uneconomic. There are currently no foliar insecticides available for Myzus persicae control in sugar beet due to resistance. Thus the ability to monitor aphid numbers, their infectivity and resistance status is an 'early warning system' for the UK Industry.
Neonicotinoid use was withdrawn in 2019. Increasing the importance of monitoring and managing the crop development alongside the Rothamsted Virus Yellows forecast which is delivered under Virus Yellows Forecasting
Outcomes / Key Message For Growers And Industry
The need for good on-farm hygiene remains critical to limit the range of pests and diseases encountered on farm and 2016 was no different, particularly after the very mild winter period, and when average December temperatures were 6.5 C higher than normal. Destroying beet remnants and crown material on cleaner loader spoil heaps and maus loading site is essential to reduce the threat from aphids and virus yellows. With the loss of neonicotinoid seed treatments in 2019 more must be done to reduce infection levels the better for the long-term stewardship of these and future treatments.
This programme includes crop monitoring and management in relation to the Rothamsted virus yellows forecast.