27 February 2026
Persistent rainfall events in the period from veraison to harvest can put vines under significant threat of disease − in particular botrytis bunch rot. Consequently, growers may be left with some difficult operational decisions.
Management strategies should be reviewed every few days as fruit ripeness and local weather conditions change. In some cases, activities including spraying or trimming may not be viable, or of limited value, and some crop loss or fruit remaining unharvested may be inevitable.
This eBulletin outlines key late-season management considerations relating to minimising botrytis infection and spread after rainfall events.
Botrytis bunch rot susceptibility
- Botrytis bunch rot, caused by the fungus Botrytis cinerea, affects dead, injured, or senescing grapevine tissue. It spreads fast in the presence of moisture, high humidity, mild temperatures (15–25°C), and when berries are damaged (by insects, heat or mechanical damage). Symptoms become more apparent as berries enlarge, change colour and begin to ripen.
- Thin-skinned varieties with compact bunches (e.g. Chardonnay, Riesling, Semillon, Chenin Blanc, Sauvignon Blanc, Pinot Gris, Traminer, Pinot Noir and Grenache) are most susceptible to infection, due to moisture retention and skin splitting. No varieties are immune to botrytis. Situations where there is bunch-to-bunch contact (often in higher yielding blocks) also lead to more rapid disease spread.
Considerations around fungicide spray decisions
Withholding periods – mandatory minimum time between chemical application and harvest that must be completed. This is termed the ‘export harvest interval’ for grapes destined for export wine as identified in the Agrochemicals registered for use in Australian viticulture booklet, commonly known as the ‘Dog book’, or the ‘withholding period’ for grapes destined for the domestic market (refer product labels).
Spray effectiveness – whether adequate spray coverage can be achieved for the active ingredient to be effective. Given the disease can start within the bunch and spread outwards, spray application to minimise botrytis on berries requires thorough coverage on the surface of and inside bunches. Late in the growing season, dense canopies can severely hamper sprays reaching this target bunch zone. Where vineyard access is possible, consider the need to trim or leaf pluck your canopy to enhance spray penetration at the bunch zone.
OH&S considerations – whether the health and safety of vineyard operators can be assured. Wet and slippery conditions can be dangerous for a tractor towing a heavy spray cart, especially on sloping ground. If safe access is not feasible, this can limit spraying or trimming opportunities.
Available fungicide options
The number of available spray options against botrytis reduces closer to harvest. Within 14 days of harvest, there is only a short list of spray options recommended for use on grapes destined for export wine. The following table is taken from Table 1 in the ‘Dog book’:
| Active constituent | Activity group | Some registered products | Export harvest interval |
| Eugenol, geraniol, thimol | BM01 | Novellus | Use no later than 14 days before harvest |
| Potassium salts of fatty acids | U1 | Ecoprotector#, Hitman | |
| BLAD | BM01 | ProBlad, ProBlad Verde | Use no later than 7 days before harvest |
| Hydrogen peroxide + peroxyacetic acid | M+M | Peracetic Acid#, PeraCrop Max#, Peratec PLUS#, Peroxy Treat# | |
| Aureobasidium pullulans | BM02 | Botector | May be used until harvest |
| Bacillus amyloliquefaciens | BM02 | Serenade Opti, Serifel |
Biological products such as Aureobasidium pullulans (Botector) and Bacillus amyloliquefaciens (Serenade Opti, Serifel) act mainly as protectants and are most effective when applied before infection, or at very early stages of botrytis development. They can be useful late season where withholding periods restrict other spray options. A. pullulans works by colonising berry surfaces and competing with the pathogen, while Bacillus-based products suppress infection through naturally produced antifungal compounds. Biologicals may be beneficial after rainfall where berries remain intact, but provide limited control once berries are split or active botrytis is present. In such cases, cultural management practices or desiccant-type products (hydrogen peroxide + peroxyacetic acid or potassium salts of fatty acids) may be more appropriate. As for general fungicide application, adequate bunch-zone coverage is essential when applying any of the products listed in the above table, and rainfall after application may reduce persistence.
If a decision is made to spray:
- Refer to the ‘Dog book’ for options based on your expected harvest date and being able to meet export harvest intervals. Some fungicide groups and/or products are restricted or prohibited from use by some wineries. Refer to Table 2 in the ‘Dog book’and your winery/grape purchaser’s guidelines before you spray.
- Know how to avoid fungicide resistance in botrytis bunch rot and apply botrytis chemicals in line with the ‘Grey mould (botrytis bunch rot) resistance management strategy’ on page 16 in the ‘Dog book’.
- Always discuss pre-harvest spraying with your winery before making any applications.
Cultural management options
Promote airflow – where vineyard access is possible, consider slashing undervine and midrow to reduce humidity and promote air flow. This can provide a viable alternative to spraying.
Hand thinning of bunches – for high value, higher yielding blocks of thinner-skinned varieties, potentially weeks out from harvest – it may be economical to hand thin bunches, minimising bunch-on-bunch contact to slow down spread of botrytis.
Drop infected bunches – for high value blocks just prior to harvest, consider dropping infected bunches ahead of the mechanical harvester, or conducting selective hand harvesting.
Harvest adjustments – work with your winery to adjust your harvest timing and picking order so that at-risk blocks are picked first to minimise botrytis incidence and quality loss.
Further information
- Agrochemicals registered for use in Australian viticulture, the ‘Dog book’
- AWRI Botrytis webpage
- AWRI Botrytis information pack
- Wine Australia botrytis resources: Botrytis bunch rot | Wine Australia
Contact
AWRI helpdesk phone: 08 8313 6600 (option 1)
Email: helpdesk@awri.com.au Website: http://www.awri.com.au
Address: Wine Innovation Central Building, Corner of Hartley Grove & Paratoo Rd, Urrbrae (Adelaide), SA 5064
Acknowledgement
This eBulletin is supported by Wine Australia with levies from Australia’s grapegrowers and winemakers and matching funds from the Australian Government. AWRI is a member of the Wine Innovation Cluster in Adelaide, SA.
