While many regions are now well into the thick of harvest, some regions are experiencing unfavourable late season weather conditions that are conducive to the development of botrytis.
Control options can be costly. To make an informed decision, establish whether or not disease severity is still at an acceptably low level. You will need to discuss the thresholds for crop acceptance with your grape purchaser. Typical limits are around 3% (for all diseases and moulds). If disease severity is low, hot dry weather may result in the first wave of diseased berries drying up naturally. Under cooler but dry conditions, moisture from overnight dews may promote further, but slow, disease development so practices that promote airflow and reduce humidity in the fruit zone are helpful.
There are a range of chemical options available, however spraying effectively late season is challenging because of the difficulty in obtaining good coverage of bunches and berries. There is a strong argument not to spray when botrytis is present in very tight bunches that are leaking juice from berries being pushed off the rachis (main stem) because further breakdown of this fruit is likely, with or without spraying. In this situation, hand removal of affected bunches or selective harvesting may be an option.
If you are within 30 days of harvest, the chemical options for botrytis control are listed in the table below. These recommendations are for fruit destined for export wine. Agrochemicals applied to fruit destined for the domestic wine market have shorter withholding periods and these are found on the label.
|Active Constituent(s)||Activity group||Some registered products||Restrictions on use|
|Potassium salts of fatty acids||U1||Ecoprotector||Use no later than 14 days before harvest|
|Hydrogen peroxide + peroxyacetic acid (suppression only)||M + M||Peratec, Peroxy Treat||Use no later than 7 days before harvest|
|iprodione||2||Chief Aquaflo, Corvette Flowable, Corvette Liquid, innova Iprodione 500 Aquaflo, Ippon 500 Aquaflo, Ipral 250, Iprine 250, Iprine 500, Iprodione 250, Iprodione Aquaflow 500, Iprodione Liquid 250, Rovral Aquaflo, Rovral Liquid, Subscribe, Transact||Use no later than 7 days before harvest. Consult your winery/grape purchaser before spraying within 30 days of harvest|
For further information on the management of Botrytis bunch rots closer to harvest please consult the GWRDC factsheet prepared by Dr Kathy Evans and Dr Bob Emmett http://research.wineaustralia.com/wp-content/uploads/2011/12/Pre-harvest-botrytis-management.pdf.