Wednesday, 1 August 2012

Downy Mildew

Downy Mildew "oilspots"
Unfortunately we have found evidence of Downy Mildew on the vineyard in Blocks A and C. Initial symptoms are usually seen on the leaves, which show yellow "oilspots" on the leaf surface. It is caused by the fungus Plasmopara viticola and is potentially a devastating disease as it can spread very rapidly through the vineyard causing the foliage to die as well as infecting the grape bunches.

Downy Mildew infected grapes
Downy Mildew only occurs in specific wetness and temperature conditions. There has to be 10mm or more of rainfall with a temperature of 10C over a 24 hour period (often referred to as 10:10:24 conditions) with rain towards the end of the 24 hour period followed by several hours of leaf wetness. It spreads when overnight conditions are 13C or more and several hours of leaf wetness occur after dawn. The fungus also produces white "downy" patches on the underside of the leaves.

The only organic approved fungicides effective against Downy Mildew are based on copper hydroxide and copper sulphate. However we are restricted to using small amounts and they will only help prevent the fungus from spreading and won't eradicate existing infections.

Alex will be spraying the effected areas with copper today and the rest of the vineyard with potassium bicarbonate which may also help.

Not a good weather year for the vineyard!

1 comment:

  1. Once the mildew attacks the plant, it spreads very easily and a gardener will soon notice white patches on the rose bush. The fungus eventually sucks all of the nutrients and water from the leaves, which in turn kills the leaves. The leaves eventually shrivel up and fall off of the bush completely.

    www.mould-removal-toronto.ca

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