19 December 2024
With the Bureau of Meteorology predicting warmer than average days and nights across much of the country for the January to March 2025 period, this eBulletin provides some tips for managing vineyards during hot weather conditions.
What impacts can excessive heat have on the vineyard later in the season?
Berries are most susceptible to heat damage from veraison (berry softening) onwards. Visible damage to berries caused by heat can be seen in the form of sunburn and shrivel, which can reduce yield and quality. Excessive heat may also exacerbate soil moisture deficits, potentially leading to drought stress if adequate plant water supply is not maintained. In particular, avoiding severe moisture stress during the period from veraison to harvest is important to prevent defoliation. Leaves play a pivotal role in maximising berry sugar accumulation, ensuring even ripening and protecting grape bunches from sunburn. The latter is particularly important for white varieties.
How can you protect a vineyard from the effects of extreme heat?
There are a range of practices that can help protect a vineyard and grape bunches from extreme heat.
Irrigate to cool the vineyard and maintain a healthy canopy
- Several days before hot weather is forecast, apply additional water to re-wet as much of the rootzone as possible to maximise transpiration cooling prior to the heat event.
- During hot weather, water vines before the hottest part of the day, such as during the evening or early morning, to reduce water loss from evaporation. If using overhead irrigation, apply at night to avoid foliage burn, especially in cases where water is saline.
- After a heat event, continue to irrigate to reduce soil temperature and replace lost soil moisture.
Minimise direct sunlight exposure of fruit through targeted canopy management
- Apply variable canopy management techniques to the different sides of the canopy. This can assist to maintain leaf layers and minimise direct exposure of bunches to sunlight on the hotter afternoon sun side of the canopy, while still encouraging air flow into the canopy. For example, apply only a partial wire lift on the western side of north-south oriented vine rows to have shoots flopping down to shade bunches, or leaf pluck only the eastern side of the canopy.
- Delay planned wire lifting or leaf removal activities that could increase bunch exposure until after a heat event.
Increase cooling effects in the vineyard
- Shade the soil surface to reduce radiation from bare soil. This can be achieved by maintaining a ground cover in the mid-row, or through mulching, composting or side throwing slashings undervine.
Minimise berry burn from sulfur
- Be aware of the impacts of applying sulfur in warm conditions and do not apply during the heat of the day. The optimum temperature to apply sulfur is between 25°C and 30°C. Applying sulfur when temperatures are above 32°C, particularly when humidity is above 70%, can result in phytotoxicity (burn), which can cause berry scarring and splitting and affect berry expansion.
Consider the use of a sunscreen product
- Application of a particle-film technology product (e.g. kaolin clays) as a sunscreen to reflect UV light and reduce radiative heating of leaves and berries may be considered. Such products are not treated as agricultural chemicals and do not appear in Agrochemicals registered for use in Australian viticulture (the ‘Dog Book’). They are not regulated by the Australian Pesticides and Veterinary Medicines Authority (APVMA) and typically do not have a maximum residue limit or label-mandated withholding period associated with use. NOTE: Always seek advice from your grape purchaser prior to application of a sunscreen product.
Further information
- Visit the Climate and weather page on the AWRI website
- Refer to AWRI’s information pack of articles on heatwave management
- Refer to the Bureau of Meteorology’s Heatwave Assessment Service, which includes heatwave maps, warnings, forecasts and assessments.
Assistance
For assistance with any technical grapegrowing or winemaking questions, contact the AWRI helpdesk on helpdesk@awri.com.au or 08 8313 6600. Between 20 December and 6 January, emergency assistance is available from:
- Adrian Coulter on 0448 736 145 for winemaking issues
- Suzanne McLoughlin on 0427 945 259 for viticulture issues.
All non-emergency queries during this time should be sent to helpdesk@awri.com.au for response from 6 January 2025.
Acknowledgements
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.