Relationship between canopy reflectance and yield loss due to disease in barley

Reflectance from barley field trial plots was measured to determine whether it could be used as an accurate estimate of disease and yield response to fungicide, and whether this was consistent over a range of agronomic factors. Three trials were used to test the effects of cultivar, assessment date, fungicide and dose, different disease and fertiliser. Correlations with predominant disease and resulting yield loss were high, often better than visual disease or green leaf area measurements alone. Certain ratios of two reflectance wavelength measurements were more robust predictors than single wavelengths. Cultivar and development stage had a large influence on measurements and calibration for such morphology-based characters would be essential for practical deployment. Whilst weather conditions and solar angle restrict opportunities for usage of reflectance tools such as the‘Cropscan Radiometer', it may prove useful in crop loss assessments as an additional objective tool.