Objective measures for powdery mildew

Powdery mildew compromises wine quality. Visual inspection, currently used to estimate disease severity, is subjective and prone to inaccuracy. Research was undertaken to improve visual assessment and to develop objective measures. A diagrammatic key and smartphone app, with supporting online training resource, were developed, trialled in Australia in 2015 and released globally in 2016. A DNA-based assay (qPCR) was developed for absolute quantification of powdery mildew fungus in grapes. Mid- and near-infrared spectroscopy proved insufficiently sensitive to discriminate levels of powdery mildew severity critical to the sector. Arachidic fatty acid was identified as a potential biomarker for quantifying powdery mildew on grapes.