Thursday, June 7, 2012

Confirmed case of strobilurin-resistant Powdery Mildew

Strobilurin-resistance has now been confirmed by researchers at the South Australian Research and Development Institute (SARDI).

The strobilurin group (stroby's) is the active fungicide in Group 11 (Pre-2009 Group K or QoI mode of action) fungicides such as Amistar, Cabrio and Flint) have been used in Australian vineyards for powdery mildew control for approximately 10 years.

In a recent trial at the SARDI Lenswood Research Centre in the Adelaide Hills, neither Amistar nor Cabrio controlled powdery mildew on infected chardonnay vines. The researchers, led by Dr Trevor Wicks, confirmed strobilurin resistance by the presence of the G143A gene in powdery mildew samples from the stobilurin-treated vines.

Dr Wicks: “This is the first confirmed case of strobilurin resistance of grape powdery mildew in Australia, although some cases of poor performance of this fungicide group have been noted in Australian vineyards.

Even though the trial vines had been subject to more strobilurin sprays than recommended commercially – and powdery mildew was already well established – the result demonstrates the potentially rapid onset of resistance typically seen, once strobilurin-resistant populations reach a critical level.

Grape growers are therefore advised to adhere to the new two-application restriction for strobilurin fungicides, and to follow strobilurin use with alternative chemistry – to help to prevent or delay the development of strobilurin-resistant powdery mildew in Australian vineyards.”

Powdery mildew infection on berries at growth stage EL-30-31 (Berries 3-7mm).

What does this mean for my vineyard?

 

There is a risk of powdery mildew resistance developing to strobys (Cabrio, Flint, Amistar) in commercial vineyards as it has in the SARDI trial site. Strobys have been applied twice a season in some vineyards for 3-5 years as part of their fungicide programme. This means it has been applied 6-10 times. This is approaching the point at which resistance develops.

Stroby resistance develops quickly and is a permanent issue.

If you have been using strobilurin fungicides in the past consult with DJ's for other options. Regular rotation of fungicide products for powdery mildew is advised as part of resistance management guidelines.

Link for more information - 

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