Powdery mildew of grapevines in Western Australia

Page last updated: Tuesday, 4 May 2021 - 10:41am

Management

If powdery mildew was a problem last season, it is most likely that high levels of overwintering infected buds and chasmothecia will be present in the vineyard. Early season management is essential.

If powdery mildew was not a problem last season, monitoring and appropriate management options should be considered. Weather conditions early in the season will affect management decisions to prevent epidemics occurring later in the season.

Vineyard establishment

Consider orientation of rows in the direction of prevailing winds. Select varieties and clones that have open bunches. For wine grapes consider planting on rootstocks that reduce vegetative growth. Avoid overcrowding. Select trellis types that open up the canopy.

Cultural

Canopy management practices that permit good air circulation, spray penetration and filtered sunlight exposure are highly beneficial. Some of these include pruning methods, shoot training, shoot thinning, leaf plucking, vine trimming and hedging. Nitrogen fertilisers should also be used with caution to avoid excessive vegetative growth.

Biological

Currently there are no commercially available biological control agents registered for powdery mildew control in Australia. Ampelomyces quisqualis (a parasitic fungus of powdery mildew) has been reported to control the chasmothecia stage of Erysiphe necator, and has been reported in some vineyards. Fungus-eating mites such as the Tydeid mite and beetles have been reported to reduce powdery mildew colonies on vines.

Chemical

There are several chemical groups available for powdery mildew control in Western Australia. The chemicals registered for use on powdery mildew for the production of wine and table grapes are listed in the Viticulture spray guide for Western Australia. Further application requirements for the control of grapevine powdery mildew are listed in the Australian Wine Research Institutes (AWRI) 'Dog Book'.

Early season control is the key. The majority of chemicals currently registered for this disease are registered for use as a preventative option before infection has occurred. A preventative spray program reduces the risk of disease development and damage but increases the number of sprays needed.

Key aspects of preventative spraying

  • In periods of rapid vine growth spray intervals of 7-10 days may be required to protect new growth.
  • If temperatures of 35°C or greater occur disease development is slowed and spray intervals of more than 14 days can be used.
  • Fungicide application just before flowering and during the five weeks after are the most important as these protect the berries during the period when they are most susceptible to powdery mildew.
  • In most seasons four to six applications of fungicides per season will be adequate to control powdery mildew.
  • Sulphur should be used as an early spray to prevent mite damage. Excluding sulphur applications from spray programs may give rise to mite problems.
  • After veraison additional sprays are only required if build up of disease on foliage and bunch stalks is present. For table grapes it is essential to maintain fresh, green, disease free foliage and bunch stalks until harvest commences.

Reliance on monitoring for powdery mildew symptoms can reduce the amount of chemicals applied but involves a higher level of risk of disease development and damage if early symptoms are missed

Fungicide resistance

Due to the ability of Erysiphe necator to sexually reproduce within Australian vineyards and the potential for multiple life cycles over a single growing season, it is considered medium risk for the development of resistance to fungicides used to manage it.

The continual use of one fungicide or one group of fungicides increases the risk of resistance developing to that fungicide or that group of fungicides. To reduce the risk of resistance developing within your vineyard always read the chemical label and regularly consult the resistance management guidelines for grapevine powdery mildew produced by Croplife Australia.