Since 1996, neonicotinoid insecticides have been an effective regulator of M. persicae, driving infection rates down to ≈1%. However, with the loss of treated seed, it is expected that large scale infections will likely return to pre-1994 levels when outbreak years were common. Qi et al. (2004) estimated that at least 16% of the sugar beet crop would be infected with virus yellows if neonicotinoid treated seed is not used. This is our lowest best estimate for the 2019 season in the absence of vector control, although it is conservative and may be elevated to 1974 levels that saw infection rates soar to >40%. The benefits of providing these model outputs are demonstrable - growers will be better able to time their control measures, securing yields and increasing yield predictably for the industry. Targeted interventions are also likely to reduce the prophylactic use of insecticides and have wide scale environmental benefits.
Models have attempted to predict virus incidence over four decades (Watson et al. 1975; Harrington et al. 1989; Werker et al. 1998; Qi et al. 2004). Rothamsted Research has been supplying the results of the Qi et al. (2004) model to the BBRO under contract for more than a decade. This model accurately predicted virus yellows incidence for neonicotinoid treated seed, but the predictions for untreated seed was more uncertain. In 2018, Rothamsted statisticians updated the model to include the correct parameter specification, hereafter referred to as model Qi (2004) v1.1. We propose to update Model v1.1 progressively to v1.5, incorporating a number of additional system components, and allowing us to provide an estimate of the incidence of virus yellows without treated seed as a function of sowing date (either 15 March, 30 March, 15 April, or a more detailed set of dates) at the factory