Powdery mildew is a serious disease of grapevines worldwide that can reduce both yield and quality of grapes. Assessment of powdery mildew is undertaken during the growing season and close to harvest to inform decisions about fungicide applications and quality and price, respectively. Many Australian wineries have a threshold for powdery mildew severity (percentage of bunch surface area affected) of 3-6%. A smart-phone app, PMapp, has been developed to facilitate recording powdery mildew on bunches, to calculate incidence (percentage of bunches of total affected) and severity "on the run" and to capture data in a spreadsheet for subsequent analysis. PMapp includes a key showing increments in bunch surface affected of 2% in the 0-12% range and approximately 140 computer-generated images to help assessors to determine area affected. The app also allows assessors to test their area assessment skills. PMapp has been developed in close consultation with the project industry reference group (IRG), comprising viticulturists from several major wineries, independent assessors and researchers. IRG workshops have guided all aspects of PMapp, from configuration of the assessment screen to the inclusion of the 2% increment key.
An online resource to assist recognition of powdery mildew and area assessment is being developed.