Ecologically engineering a sustainable sugar beet landscape matrix informed by molecular tools, satellite imagery and bioeconomics.

Sugar beet, a crop which meets half of domestic sugar demand, is grown on a thousand square kilometres of arable land in the UK, mostly in East Anglia. However, the crop is threatened by a complex of three viruses, known collectively as virus yellows, that dramatically reduces yield by compromising the plant's ability to photosynthesize. The viruses are transmitted by aphids and, for 30 years up until 2018, sugar beet seed was coated with a neonicotinoid seed treatment that effectively and systemically controlled aphid feeding and thus the transmission of virus yellows. However, neonicotinoid treatments were widely cited has having detrimental non-target impacts, most notably changing the behaviour of pollinators, particularly bees. As a result, the EU banned the use of neonicotinoid seed treatments on 27th April 2018.

Following the ban, a confluence of warm weather, early sugar beet emergence and abundant aphids saw the 2020 crop severely affected by virus yellows and growers experienced average yield losses of 38%, which were valued at £43 million and rose to 100% losses in parts of Cambridgeshire. In response, the BBRO, the levy board charged with ensuring that growers of sugar beet thrive, applied to Defra for a derogation to use neonicotinoid seed treatments in sugar beet in both 2021 and 2022 if our 'Rothamsted Model' predicted that more than 9% (2021) and 19% (2022) of the sugar beet crop yield would be lost to virus yellows at harvest. In 2021 these conditions were not met, but in 2022, a derogation was granted by Defra to use the neonicotinoid Cruiser SB seed treatment.

However, neonicotinoid seed treatments are not a sustainable practice for the future, especially considering new agricultural policy under the ambitious environmental land management schemes, particularly the Sustainable Farming Incentive (SFI). Projecting forward, the permission to use of neonicotinoids could be based on regional risks, limiting the environmental impact. Alternatively, growers and the industry could decide collectively to move away from neonicotinoids altogether or be mandated to do this by policy makers. To produce a sustainable and economically viable sugar crop under either of these scenarios, we would need to know how the virus transmission pathway behaves and scales to then make predictions about its impact at harvest. Using molecular tools and a hyperspectral drone to detect leaf yellowing, we will track the development of disease-infected sugar beet over time and, examine the presence of virus yellows in the crop, identifying key non-crop virus reservoirs in field margins and tracking local spread into the adjacent crop. This is essential to progress to the next generation of virus yellows models, a future ambition that will provide a robust decision support tool for aphid management. To further progress this modelling ambition, we need to understand virus risks at the landscape scale and plan to use satellite imagery to quantify the extent of field margin habitats, a potential source of virus yellows, and other crops that support aphids during winter. It has not yet been shown statistically that oilseed rape planted nearby to sugar beet increases the threat of the virus vector, but many growers adopt to this view. Using extensive 2020 sugar beet vector and virus incidence data held by Rothamsted, we will use satellite images from 2020 to derive proximity measures to estimate the threat posed by the network of nearby oilseed rape crops. A bioeconomic model that incorporates farm economics and the biology of the sugar beet system, will be used to explore how the risk of virus outbreak affects profitability within the context of different payment options and under different landscape scenarios. There is imperative to understand this urgently to meet both food security and sustainability goals.

This proposal will deliver the science needed to progress to a farming future for sugar beet that will suit all.

In England, sugar beet is grown on 100,000 ha of arable land, meeting half of domestic sugar demand. Yields are threatened by virus yellows (VY), comprising beet mild yellowing virus, beet chlorosis virus and beet yellows virus. These three viruses, all transmitted by the primary vector Myzus persicae, decrease the ability of the infected leaf to photosynthesize, therefore reducing yield. Given the recent 2022 derogation following our 'Rothamsted Model' forecast, the neonicotinoid seed treatment, Cruiser SB, has been authorised for use. Derogations are a temporary policy measure; our proposal looks to the future. We will address how the threats to sugar beet can be understood and mitigated.

We will develop a low cost, accurate LAMP assay to target all three virus types in the field and use this to quantify the number of effective 'non-crop' plant hosts that act as a virus reservoir for each virus type. We will estimate the weekly rate of virus spread under field conditions from a single inoculated source using field counts, hyperspectral drone technology and confirmatory LAMP assays, underpinning the next generation of models to provide more accurate forecasting and hence support better management decisions. The landscape matrix is key to understanding VY risk. Supported by a wealth of virus incidence data held by Rothamsted and using expertise at Cranfield, we will use satellite imagery to estimate the threat posed by the network of nearby oilseed rape crops and characterise the extent of field margins, a potential source of VY, measuring the spillover of VY into the adjacent crop. A bioeconomic model, led by Bristol, will be used to capture a grower's management decisions under different land use and payment options.

Our work is much needed. It will explain how the VY transmission pathway functions locally and at scale and will show how improved land use and crop rotation planning based on this knowledge could potentially reduce the virus risk.