In sink-limited spring barley crops, light interception by green canopy does not need protection against foliar disease for the entire duration of grain filling

• Published in: Field crops research 2019-06, Vol.239, p.124-134
• Main Authors: Bingham, Ian J., Young, Caroline, Bounds, Philip, Paveley, Neil D.
• Format: Article
• Language: English
• Subjects: Fungicide timing; Hordeum vulgare; Integrated pest management (IPM); Shading; Yield
• ISSN: 0378-4290; 1872-6852
• DOI: 10.1016/j.fcr.2019.04.020

•Canopy light interception does not need protection for the whole grain filling period.•Fungicide applied after ear emergence prolonged light interception but not yield.•Applications at stem extension and booting maximised yield when disease was severe.•Apparent sink-limitation of yield was observed at high and low yielding sites.•Optimum fungicide timing was not influenced by the yield potential of the site. Disease management in cereals is heavily reliant on the use of fungicides, but development of anti-microbial resistance, effects on non-target organisms and persistence of active ingredients in the environment and food chain challenge the sustainability of this approach. Better targeting of fungicides according to crop need within an integrated pest management (IPM) programme could improve the sustainability of disease management. The objectives of the present study were to determine 1) the duration of protection of post-anthesis canopy light interception required to maximise the yield of spring barley and 2) to relate this to the response of crops to timing of fungicide applications. As the yield of spring barley is considered to be sink-limited (limited by the number and storage capacity of grains) rather than source-limited (limited by the amount of carbon assimilates available for grain filling) in many environments, we hypothesised that the canopy would not need to be protected for the entire grain filling period. Field experiments were conducted at two sites in the UK (Edinburgh and Herefordshire) over four years, providing contrasting climates and soil types. Shading was used to determine the response of grain filling to reductions in light interception over defined intervals, thereby mimicking effects of foliar disease on light interception, as shading is easier to control than the onset and duration of disease epidemics. Shades giving ˜67% reduction in photosynthetically active radiation (PAR) were erected over plots of disease-free crops at weekly intervals commencing at flowering and leaving them in place until harvest. The required duration of protection of light interception was estimated as the period from flowering to the time at which the onset of shading had no effect on yield. In a separate experiment the response to five fungicide timing treatments was determined on three relatively disease-susceptible varieties. Timings were the start of stem extension (referred to here as T1 only) and T1 followed by a second application at either