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Abstract

BYDV is a persistent luteovirus virus transmitted by aphids feeding on wheat, barley, grasses or other cereal crops. Crops are susceptible to this virus at early growth stages through to growth stage 31 (first node detectable). Infected plants initially have bright yellow upper leaves but later become stunted and produce fewer and smaller grains. Infections spread from a single infected plant to larger patches forming around the initial source of infection as aphids move through the crop. In the UK, the bird cherry-oat aphid (Rhopalosiphum padi) is the main virus vector but in some regions the English grain aphid (Sitobion avenae) is equally important (White et al., 2023). Management of BYDV has traditionally focused on controlling primary infections (infected aphids flying into crops) before secondary infections (infected aphids moving within crops) develop. However, this approach to pest management has changed dramatically in recent years with the loss of neonicotinoid seed treatments and the appearance of moderate levels of pyrethroid resistance in the English grain aphid. Control still relies on foliar applications of pyrethroid insecticides, meaning that management of BYDV vectors is the same today as it was forty years ago. Indeed, continued reliance on the use of pyrethroids risks development of new forms resistance appearing in BYDV vectors. It is clear then that development of effective integrated pest management (IPM) is required to sustainably manage BYDV vectors. Specifically, this can be achieved through an improved understanding of preventative, forecasting and crop protection approaches. The AHDB Strategic Cereal Farm East (2023-2029) is an example of how the industry is responding to the threat posed by BYDV by putting cutting-edge research and innovation into practice on commercial farms. The Strategic Farm is hosted by Morley Farms Ltd, a commercial enterprise that farms land owned by The Morley Agricultural Foundation (TMAF). A key objective of the Strategic Cereal Farm East is management of BYDV and this part of the research portfolio is being led by researchers at ADAS and ÌìÃÀÊÓƵ. As such, the following proposal builds on and benefits from an established collaboration between the research and commercial partners, while maintaining an independence as a stand-alone research project.

Description

Project aim: to move management of BYDV in cereal crops beyond reliance on pyrethroid insecticide application through improved understanding of methods to prevent, forecast and sustainably control aphid vectors of BYDV. Specific project objectives include:

Objective 1: Investigate the influence of varietal resistance to BYDV and crop genetic diversity on aphid vectors of BYDV. This part of the project will build on AHDB project 21120186, which has recorded variation in responses of winged and wingless BYDV vectors to winter wheat varieties and between crops with different levels of genetic diversity. The focus will be to investigate the potential to reduce the primary and secondary spread of BYDV by winged and wingless aphids. Experiments will be completed under laboratory (e.g., olfactometer/wind-tunnel, electrical penetration graphs/feeding assays), glasshouse/polytunnel (e.g., semi-field environments) and replicated trial plots at HAU as well as on-farm experiments at AHDB Strategic Cereal Farm East. Years 1 & 2

Objective 2: Investigate the potential of plant growth stimulants (e.g., silicon) and physically acting biopesticides (e.g., fatty acids) on aphid BYDV vectors. Some studies report that silicon applications lead to smaller aphid populations in wheat crops (e.g., de Oliveira et al., 2023) while in other studies effects are less clear (e.g., Rowe et al., (2020). More widely, there is increasing interest through regenerative agricultural practices to use brix measurements as a way of determining the nutritional health of the crop. These measurements are often linked to the susceptibility of the crop to pests, such as aphids, but there is a lack of evidence to support these claims. Similarly, while biopesticides are widely used in horticultural production, use of these products in arable cropping systems has yet to be fully exploited. Experiments will be completed under laboratory (e.g., aphid performance assays, biopesticide efficacy assays, electrical penetration graphs, glasshouse/polytunnel (e.g., semi-field environments) and replicated trial plots at HAU. Years 2 & 3

Objective 3: Determine the reliability of the Acrobat decision support system (DSS) for insecticide applications to prevent the secondary spread of BYDV. The recommendations provided by the Acrobat model will be compared with those from the . Detailed assessments of aphid and aphid natural enemy numbers both before and after any insecticide application will be made. These assessments will be complemented by PCR/ELISA assessments of BYDV presence in fields monitored in both the autumn and spring. Experiments will be completed on-farm at AHDB Strategic Cereal Farm East Years 2 & 4

Objective 4: Investigate trap colours to improve in-field monitoring of English grain aphid. White et al. (2023) reported that yellow water traps are effective for monitoring of bird cherry-oat aphid but that crop monitoring was more effective for the English grain aphid. Laboratory studies at HAU have also found the English grain aphid not to respond to yellow traps (unpublished data). However, Kieckhefer et al. (1976) reported that bird cherry-oat aphid show a preference for green rather than to yellow, while English grain aphid show a preference for yellow rather than green. Experiments testing colour preferences of cereal aphids will be completed under replicated trial plots at HAU as well as on-farm experiments at AHDB Strategic Cereal Farm East. Years 2 & 3

Objective 5: Investigate the role of aphid natural enemies in reducing numbers of aphid BYDV vectors in winter wheat crops. Aphid natural enemies are known to reduce populations of summer cereal aphids (e.g., Ramsden et al., 2016). However, there is little field information on the role of aphid natural enemies in reducing the secondary spread of aphid BYDV vectors (e.g., Smyrnioudis et al., 2007). Experiments recording the importance of aphid natural enemies in managing BYDV will be completed in mesocosms established under laboratory and glasshouse/polytunnel conditions as well as on-farm experiments at AHDB Strategic Cereal Farm East. This objective will also benefit from data collected by ADAS. Years 2 & 4