Main Objectives
Current BBRO recommendations are to apply a full dose of fungicide as soon as disease is seen in the crop (mid-July to mid-August) and to use a second spray if more than 20% disease is evident on untreated beet in August, if there is a risk of rust, or if the beet is to be lifted late (Stevens, 2013). Earlier work has shown a yield penalty if fungicides are applied too early (before canopy closure) but the mechanism for this is not fully understood. If disease pressures increase, as may be expected to occur with increased temperatures under climate change, the optimum timing of fungicide application will be critical to maximise disease control, alongside any physiological benefits.
Fungicides appear to result in a more persistent canopy, and in beet leaves staying greener for longer. However, the physiological impact of current fungicides (either the triazole and/or strobilurin active ingredients), in the absence of disease, has never been fully understood or quantified. In other species the so-called ‘stay-green’ impact of fungicides has sometimes been shown to be non-functional, with canopies staying greener for longer but with no associated yield gain. This project will disentangle the impact of fungicides on disease control from other, physiological or varietal effects, in terms of canopy persistence and yield formation. This will inform decisions regarding the timing, or sequence of fungicides to maximise yield.
The BBRO Crop Protection Review (Sparkes, 2014) concluded that work is required to understand the physiological response of sugar beet to fungicide application so that timing can be optimised in the absence of disease, for the current prevalent diseases, and for diseases that may increase in importance in the future (e.g. ramularia and cercospora leaf spot). Variety choice may also be important as canopy architecture and leaf colour may also be influential. Also, there is a high risk that most of the current triazole and strobilurin fungicides may not be available after 2022 due to their endocrine disruption properties (e.g. cyproconazole in Escolta). Potentially, this would mean an alternative range of active ingredients becoming available for sugar beet growers and a need to understand their physiological interactions with the next generation of sugar beet varieties.
References
Sparkes, DL (2014) Future research requirements in crop protection: the sugar beet crop. BBRO Research Report.
Stevens, M and Burks, E (2012) Fungicide strategies for maximising yield potential: lessons from 2011. British Sugar Beet Review, 80 (2), 10-13.
Stevens, M and Bowen, S (2019). Protecting autumn growth from foliar disease to maximise yield potential. British Sugar Beet Review, 87 (3), 40-43.
Stevens, M (2013) Maximising yield performance through fungicide application. British Sugar Beet Review, 81 (2), 30-34.
