The sugar beet crop faces its biggest threat from viruses transmitted by aphids since the 1970s, when sugar yields were halved in outbreak years. Two main factors account for this heightened threat. The first is the unusual ability of the main aphid vector, the Peach-potato aphid, Myzus persicae, to develop resistance to insecticides. This has led to the industry becoming heavily reliant on neonicotinoids for aphid control, more than 90% of seed being treated with these insecticides. Resistance to neonicotinoids has long been predicted and has now taken hold in parts of central and southern Europe. It is inevitable that it will reach the UK in due course. The second factor is the trend to increasingly mild winters, favouring survival of M persicae and leading to earlier and larger populations during the critical young growth stages of the crop which are most susceptible to infection and damage. It is thus essential to manage aphid control on the basis of high quality intelligence on the abundance of aphids and their insecticide resistance status to ensure that insecticides are only used when and where necessary and that appropriate products are deployed. The objective of the project is thus to optimise and sustain the use of insecticides on beet by providing forecasts and up-to-date information on the timing and abundance of aphids, their virus content and the precise insecticide resistance mechanisms present. This project will build on successful previous projects centred on data provided by the Rothamsted Insect Survey's aphid monitoring network of suction traps, with two important developments: i) testing for two new insecticide resistance mechanisms, to pyrethroids and neonicotinoids and ii) the inclusion of aphids from the Broom's Barn network of yellow water pan traps in the resistance testing in order to add information on local variability to the regional overview provided by the suction trap data. Forecasts of the timing and size of aphid migrations will continue to be provided and will aid decisions on aphid control early in the growing season of crops not using neonicotinoid-treated seed. The proportion of the crop to which this applies is likely to increase dramatically as the insecticide becomes compromised by resistance or possibly by regulation on the basis of its apparent impact on bees.
Outcomes / Key Message For Growers And Industry
- Infection with beet yellowing viruses has been shown to cause sugar beet yields to fall by up to 50% in outbreak years. Large scale infections are now rare largely due to the effectiveness of neonicotinoid insecticides that control the main aphid vector, Myzus persicae.
- In the UK M. persicae is currently susceptible to neonicotinoids but target site resistance (nicR) has been observed in Southern Europe and is expected to spread. Resistance evolution and the predicted loss of the once common UK clones suggest that there is additional uncertainty as to the future effectiveness of neonicotinoids generally.
- Should neonicotinoids be withdrawn or prove ineffective due to resistance, virus yellows could return to a situation not unlike the 1970s in which there were large-scale infections and consequently low yields.