Wednesday, March 18, 2009

Botrytis increases after rain and dew - UPDATE 18/3/2009


Steady rain plus heavy dues in the Hills have seen an increase in botrytis. Look for slippery skins as pictured. 
Growers in the Range Road area need to have a good look if further rain occurs in Shiraz with tight bunches, and other mid to late season varieties, as their harvest is still a few weeks away. 
No significant rain is forecast at this stage but heavy dews can increase the disease. These may also require a protective fungicide.

Botrytis risk -Major Varieties

High - Sav. Blanc, Riesling, Grenache, Semillon, Chenin Blanc.

Medium - Viognier, Pinot Gris, Pinot Noir, Chardonnay, big bunched Shiraz, Sangiovese, Mataro/Mouvedre, Petit Verdot, Verdelho.

LowBold - Small bunched Shiraz, Merlot.

Very Low - Cabernet Sauvignon.

There are exceptions to these rules- different vineyard sites, croploads, canopy management and chemical strategy have an effect on the amount of rain a block can receive before showing signs of disease.

Assess your vineyard and seek specific advice as is needed.

Dicarboximides - Rovral, Fortress etc should be applied as an acidic spray tank mix (water pH less than 7) to be stable. 1kg/1000lts of tartaric acid, citric acid or similar, or a commercial buffer- tradenames include AGRI-BUFFER will acidify the water and lower pH.

PMS - (Potassium metabisulphite) dries out the bunch and can help heal berry splitting. PMS rates higher than 3kg per 1000 litres are needed and the pH of the spray solution should be adjusted to between 2.9 and 3.0 using 1.5 kg 100% tartaric acid per 1000L.

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