Tuesday, December 14, 2010

Downy Mildew Update - 14/12/2010

Downy Mildew Oilspots have been seen spread from Downy Mildew secondary events in November.

We are expecting to see further spread from the Downy Mildew Secondary Event (Warm,Wet Night) that occurred on the 7th/8th of December. Oilspots from this event are predicted to become visible on or about the 16th of December.

Check vineyards now. If you find any oilspots tag them. We have found oilspots in the area roughly outlined below. Even if you are outside of this area - you still need to check for oilspots.



Above - Older oilspots have a burnt look but have white down on the underside of the leaf.

Left & Below - Oilspots can often look very plain when seen from the front, but once they are turned over the infection becomes obvious. Picture here is the same fresh Downy Mildew oilspot seen from the front and back.

The 'bag test' indicates active downy mildew.

Pour clean water into an empty, sealable plastic bag, shake the contents, then empty to leave the bag lightly moistened.

Collect fresh leaves or bunches suspected of having downy. Seal them in the bag and leave overnight in the dart at 20°C to 25°c.

Next morning, white down will have developed on the undersides of oilspots with active downy mildew or on young bunches (berries < 5 mm).

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