Virus Yellows disease is a complex of three viruses; Beet Mild Yellowing Virus (BMYV), Beet Chlorosis Virus (BChV) and Beet Yellows Virus (BYV).
These viruses are transmitted when aphids carrying the viruses feed on sugar beet. The peach potato aphid (Myzus Persicae) is the main vector.
Infection of sugar beet plants with the yellowing viruses causes chlorosis of leaves, which in turn disrupts photosynthetic, respiratory and other metabolic processes.
These changes increase the levels of amino nitrogen, sodium and potassium in roots, which negatively affects extractability of sugar during factory processing.
Once infected, yellow leaves are susceptible to attack by secondary fungi such as Alternaria alternata, which may destroy the leaf, further exacerbating yield loss.
If a crop is infected with Virus Yellows, the grower can experience up to 50% yield loss, and more if the crop suffers from other diseases, such as Cercospora.
Why is virus yellows disease such a problem in the UK?
Farmers in the UK are more severely impacted by virus yellows than growers on the continent due to the maritime climate.
Cold winters are needed to suppress aphid populations. Milder, warmer winters increase the risk of Virus Yellows to the crop, as aphids, which carry the virus, survive over winter and if they are carrying the virus, can infest the crop more readily come spring.
The year 2020 saw the perfect aphid storm, with a mild winter and an early aphid migration, leading to devastating consequences for some growers.
How have farmers protected their crop in the past?
Historically, farmers have protected their crop by using neonicotinoids seed treatments. These seed treatments protect the crop during the early stages of establishment when it is at its most vulnerable to aphid attack.
Since 2019 farmers have had no access to neonicotinoid seed treatments and therefore are limited in how they protect their sugar beet crop. Foliar sprays can be used on sugar beet during the first 12 weeks. However, many of the active ingredients in these sprays, which can provide a certain level of protection, are not being re-authorised for use on farm. This means that growers are often unable to manage the risk.
Using 2020 as an example, due to the early and sustained aphid pressure, the first virus symptoms were observed by mid-June 2020. Widespread symptom development continued throughout the summer. Nationally, 38.1% of crop was infected with virus, although infection levels ranged from 7% (Cantley) to 61% (Wissington) between the four factory areas.
NFU Sugar and British Sugar, with valuable technical support from the BBRO, applied for an emergency authorisation to use Cruiser SB on sugar beet seed for the 2021 crop. A condition of approval was that use of Cruiser SB would only be permitted if the Rothamsted Annual Aphid Forecast projected a particular threshold of aphid pressure.
In 2021 the neonic trigger was not reached due to a very cold winter which resulted in lower than average levels of aphids expected in the crop.
Similar conditions were attached to the Emergency Authorisation granted for the use of Cruiser SB on sugar beet seed in 2022. This time the model forecast an incidence of 68.9% and its use was triggered. In 2022, seed treatments coupled with timely sprays all contributed to decreasing the incidence of virus yellows in the sugar beet crop.
An application from NFU Sugar and British Sugar for the emergency use of neonicotinoid seed treatment on sugar beet seed in 2023 has been approved by the government. The authorisation has been granted on the condition that the product will only be used if the threshold for virus levels is reached.
What is NFU Sugar doing?
In September 2020, the virus yellows taskforce was established between British Sugar, NFU Sugar and the BBRO to accelerate and develop ongoing and novel pathways of research to limit the future impact of this disease across the UK industry.
British Sugar and NFU Sugar also introduced a new virus yellows assurance scheme, funded by British Sugar, which functions to mitigate a proportion of losses incurred by growers from Virus Yellows.
In future years we have estimated that the crop area could reduce by up to 25% if a long-term sustainable solution cannot be found. This group meets government officials and MPs regularly to champion the homegrown sugar industry and seek solutions to the disease.
With the technical expertise of the BBRO, NFU Sugar and British Sugar apply for emergency authorisations for plant protection products (foliar sprays and seed treatments) on an annual basis in order for growers to have access to the chemistry you need, if thresholds are met.
“Though the correct regulation of gene editing, both the food system and the environment should benefit: the former through improvements in food security, the latter through increasing biodiversity and reducing climate change.”
NFU Sugar Board Chair Michael Sly
Partially resistant sugar beet
Currently, there is one partially resistant sugar beet variety (Maruscha) commercially available for 2022 which has mild resistance to one of the three yellowing viruses that form the Yirus Yellows complex (BMYV, BChV or BYV). The yield potential in the absence of virus is low compared to existing, elite susceptible varieties. BBRO has calculated (from inoculated trials in 2019 and 2020) that growers would have to sustain 62% infection within fields before such varieties become economically viable. However, new breeding techniques, such as gene editing provide hope for growers.
Gene editing will help
The Genetic Technology (Precision Breeding) Bill focuses on stopping certain gene editing organisms from being regulated in the same way as genetic modification (GM), as long as they could have been produced naturally or through traditional breeding. Our sugar beet sector urgently requires fit for purpose, science-led regulation to pave the way for a sustainable path to tackling virus yellows disease, and therefore UK adoption of new breeding techniques will provide an important opportunity for the sugar beet sector to reduce the impact of pests and diseases, while driving improved yield over time.
“New breeding techniques should be seen as part of a broad set of new tools and approaches that enable UK farmers to take a more sustainable path, including IPM and resource use efficiency.”
NFU Sugar Board chair Michael Sly
NFU Sugar board Chair, Michael Sly said: “Using conventional breeding to find a genetic solution to virus yellows disease is difficult because three different viruses are responsible for the disease. Trying to identify resistance genes in wild relatives, which can then be bred into conventional varieties, is a slow, long-winded process. A targeted gene-editing approach provides the opportunity to speed this process up, potentially providing a future solution to Virus Yellows.”
“In addition to addressing diseases caused by viruses, gene editing also has the potential to help provide solutions to pests and diseases where plant protection products are not available, for example, fungal diseases such as, Cercospora and pests, such as free-living nematodes.
“Gene editing also has the potential to help address issues such as drought tolerance and improved nitrogen-use efficiency. Though the correct regulation of gene editing, both the food system and the environment should benefit: the former through improvements in food security, the latter through increasing biodiversity and reducing climate change. An example from sugar production is that it takes one third less water to produce sugar from beet rather than cane.
"If we can produce more sugar from higher-yielding, genetically engineered sugar beet, we could reduce cane sugar imports. Therefore, it is important that the UK has access to this technology to allow us to compete with countries where these technologies are already routinely used.”
“However, we do not think biotechnology is a silver bullet. It is important to note that gene editing does not negate the need for plant protection products completely as the nature of pests and diseases evolve over time. Rather, it forms part of a wider, integrated solution to the problems the sugar beet sector faces.
"New breeding techniques should be seen as part of a broad set of new tools and approaches that enable UK farmers to take a more sustainable path, including IPM and resource use efficiency.”