Powdery mildew does not shut down for Christmas

Weather conditions over the festive season can be very favourable for the spread of powdery mildew, often referred to as the ‘dry weather disease’, with young berries particularly susceptible to infection.

Growers should always manage powdery mildew preventatively through a sound early-season spray program, including appropriate fungicide choice, along with effective spray timing and coverage. This is far better than trying to manage the disease after infection is evident (curatively).

However, preventative management isn’t always achievable, so if powdery mildew is detected later in the season, it is important to treat as early as possible. Bayfidan® fungicide can play an important role in protecting the quality and value of grapes, by providing cost-effective systemic control of fungus within the leaf, as well as offering residual activity to control further spread of the fungus. This makes it much more effective than many other fungicides, some of which only control spores landing on the plant.
Constant monitoring for powdery mildew is imperative to ensure grapes are disease-free, as tolerance levels for powdery mildew may be low for some buyers. This could lead to rejection of fruit if infected grapes are found.

If powdery mildew is detected in the vineyard, despite adhering to a spray program, it can usually be related to;
• Delayed spray timing
• Extended spray interval
• Poor spray coverage
• Poor chemical choice

WINTER
Powdery mildew overwinters as fungal growth in diseased buds or as cleistothecia (spore bodies) on leaves, stems and bark.

SPRING
Diseased buds develop into stunted ‘flag’ shoots. Cleistothecia release spores after 2.5 mm of rain or irrigation. Spores spread to developing leaves and bunches.

SUMMER
During early summer a new generation of spores is formed every 5–10 days and spread by wind throughout the vineyard in mild cloudy weather conditions, ideally around 22–28oC.

WINTER
Cleistotheia remain on cordons, canes and decaying leaves. Fungal strands remain inside the dormant bud.