Digital tools for vineyard management: A diagrammatic key for assessing powdery mildew severity on grape bunches

During visual assessment of powdery mildew (PM), bunches are scored according to disease severity categories (% of bunch surface area affected of total area assessed). The quality of assessment depends on the experience and training of the assessor in disease recognition and area estimation. Diagrammatic keys are often used to guide assessment. A key for use in commercial vineyards should assist users to differentiate small increments in severity in the low range because rejection thresholds are typically 3-6% severity. Here we present a key developed in consultation with wine company assessors and representatives to assist preharvest assessment.