New app to assess powdery mildew on grapes

Visual assessment of the grape and wine sector's most costly disease, powdery mildew, will be easier with a new, free smart-phone app developed by University of Adelaide researchers and collaborators.

The recently released iPhone/iPad and Android app, PMapp, will help grapegrowers and wineries make informed decisions about the quality and price of grapes.

The development of PMapp has been supported by Wine Australia as part of a wider research project seeking to establish objective measures for quantifying powdery mildew. The app development has taken place in close consultation with a project reference group of viticulturists, wineries, independent assessors and researchers.

"Powdery mildew is a serious disease of grapevines worldwide and, in Australia, has an estimated annual cost of $76 million through yield loss and the cost of control," says project leader Professor Eileen Scott, Professor of Plant Pathology in the University's School
of Agriculture, Food and Wine.

"It causes serious quality issues with bad flavours and aromas in wine and we've seen that with small amounts of the surface area of Chardonnay bunches affected by powdery mildew there is an oily 'mouth-feel' in the resulting wine.

"The wine sector therefore has a very low tolerance of powdery mildew on grapes with downgrading at 3–6% or rejection when disease is more severe. This is a costly disease for the grape and wine community.

"But powdery mildew is hard to assess – the disease is ubiquitous, but symptoms can be hard to see, or easily confused with dust or spray residue.

"PMapp is a simple tool that facilitates efficient assessment and recording of the severity and incidence of powdery mildew in the vineyard."

Dr Liz Waters, Wine Australia Research Development and Extension Portfolio Manager, says tools such as PMapp help support decision making to build grape and wine excellence in the Australian sector.

"The ultimate aim of research and development in this area is to develop objective analytical methods to assess powdery mildew infection levels. Although visual assessment is subjective, this new app will facilitate these assessments and enable efficient and cost-effective vineyard practices," says Dr Waters.

PMapp allows the user to quickly assess visually the severity of powdery mildew on each bunch of grapes (an estimation of the percentage of the surface area of the bunch covered) by matching it with a computer generated image. The app calculates the proportion of bunches affected (the disease incidence) and of surface area affected (severity) and reports the data in a spreadsheet for subsequent analysis. A key reference and browser of images built into the app also help the user familiarise themselves with various disease patterns and severities. A website to support the app is currently being developed and is scheduled for release at the end of January.

The PMapp is now available on Apple's App Store or Google Play.