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PMapp and supporting website: New tools to facilitate assessing powdery mildew on grape bunches

conference contribution
posted on 2023-05-24, 16:23 authored by Scott, ES, Emmett, RW, Birchmore, W, Perry, W, Petrovic, T, Kravchuk, O, Zanker, T, Katherine EvansKatherine Evans

Powdery mildew has the potential to affect wine quality. Many Australian wineries use a threshold of 3-5% powdery mildew severity on bunches close to harvest to inform decisions about quality and price. Assessment is based on visual estimation, which is acknowledged to be subjective. The quality of assessment strongly depends on the experience and training of field assessors in disease recognition and estimation of bunch area with disease. In collaboration with wine sector representatives, a free application, PMapp, for Apple and Android smart-phones and tablets was developed to facilitate assessment of powdery mildew in vineyards and adoption of uniform assessment practices. An assessment recording screen presents the user with categories from trace (0.5%) to 100%, with 1% increments from 1-10% and larger increments thereafter. The severity score for each bunch assessed is entered and the screen displays cumulative bunch count, incidence and severity on a row and patch basis. The data, including information about date, time and location (with latitude and longitude), can be exported on completion of the assessment for subsequent analysis. PMapp has a bank of computer-generated images of bunches to facilitate assessment of area, a self-calibration tool that allows the user to check his/her accuracy and a diagrammatic key with 2% increments in the range 2-12% for those who find a key helpful. PMapp was released in Australia in December 2015 and worldwide in November 2016 and was downloaded over 2700 times by May 2017 (Australasia 60%, North America 21%, Europe 17%).

A website to support use of PMapp was developed at the request of wine sector collaborators. This website ( offers a best-practice, stepwise guide to in-field assessment with links to training for disease recognition, area assessment and the diagrammatic key. The disease recognition component comprises 28 high-resolution photographs, in triplicate, of powdery mildew on red and white bunches at veraison and close to harvest; each photograph has areas outlined that might represent surface with visible powdery mildew. The user is asked to select the image (of three) that has powdery mildew outlined most correctly. The area assessment component features the computergenerated images in PMapp. The user takes a “test” comprising low-range (0.5-15%, 20 images) or fullrange (0.5-90%, 30 images) severity in which certain images are shown three times to assess repeatability. Output comprises a chart showing agreement of the estimate with the actual image (Lin’s concordance value), repeatability and time taken for each image. Output can be printed and used as proof of capability, should an employer require evidence. Results are retained and can be accessed by the user, via log-in and password, so that performance can be tracked and analysed over time.

Two of Australia’s largest wine companies used these resources in 2017. One incorporated the recording component of PMapp into their standard operating procedures and made 375 assessments. The other used the website, image bank, self-calibration and key components to train new field staff (8 in 2017) to assess disease. Informal feedback from leaders in the sector indicates that these resources have improved the quality of disease assessment.


Wine Australia


Publication title

8th International Workshop on Grapevine Downy and Powdery Mildew 2017


Tasmanian Institute of Agriculture (TIA)

Event title

8th International Workshop on Grapevine Downy and Powdery Mildew 2017

Event Venue

Corvallis, USA

Date of Event (Start Date)


Date of Event (End Date)


Repository Status

  • Restricted

Socio-economic Objectives

Wine grapes

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    University Of Tasmania


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