Botrytis risk is most severe where excessive nitrogen has been used, where air circulation is poor, or where apple moth or other factors have damaged bunches. Rotted berries typically have a gray cast of the mycelium and spore-bearing structures present which gives the disease its common name - Grey Rot.
Conventional Late Season Fungicides
Dicarboximides - Rovral, Chief, Corvette 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.
Organic Botryticides Options.
Information for control of late season Botrytis in Vineyards is difficult to get reliable, scientific trial results on.
Peratec® is a formulation of peracetic acid and hydrogen peroxide. It may work as a broad spectrum surface sterilant. If you are in a tough situation it maybe a valid option, but note the following; Peratec® can be difficult product to find in retailer stores. It is recommended that this product is pre-ordered and stocked in your chemical store for use as weather requires.