The extreme hot weather conditions, which were experienced since the first week of January 2013 across many parts Australia, has led to a number of bush fire events, conditions of which could also possibly lead to increased incidence of smoke exposure in vineyards.
The presence of smoke taint in fruit is governed by a number of factors including proximity and type of fire, intensity, duration of smoke cover, prevailing wind and weather conditions etc.
The timing of smoke exposure to grapevines is also important; there is low sensitivity to smoke uptake in the growth period to flowering, low to moderate risk through to veraison, and beyond veraison through to harvest, grapevines can be highly susceptible.
Currently, it has been reported that in many of the cooler regions, vine growth stage is between bunch closure and veraison. Whilst this may be in the lower risk category at the moment, the situation may change if fire and smoke events continue.
The AWRI recommends grapegrowers and winemakers follow the below testing regime to ensure grapes are free from smoke taint and remain fit for purpose:
- If your region has experienced a smoke event, wait until ripening has proceeded beyond veraison before testing for smoke taint.
- There is considerable variation across a vineyard, so follow a sampling regime that takes into account topographical features of the vineyard and follow the same sampling regime when carrying out repeated sampling.
- Small lot fermentation is highly recommended in assessing potential to produce smoke taint in wine. The AWRI has developed a basic fermentation protocol which is available on the AWRI website.
- Analytical support is available and this is also summarised on the AWRI website (click here for analysis FAQ)
More detailed information is available via the following link
https://www.awri.com.au/information_services/current-topics/smoke-taint/
Most grapegrowing regions recorded spring rainfall well below average; it is a timely reminder to ensure that water status is maintained.
The effect of extreme heat on grapevines depends on the timing of the heat event relative to the grapevine growth stage. Flowers are highly susceptible and poor fruitset may occur from a heatwave during flowering. After veraison (as grapes soften) grapes become more prone to shrivel or sunburn. Dark coloured grapes directly exposed to the sun may get much hotter (up to 15°C) than the surrounding air temperature.
Irrigation management is critical before, during and after a heat event. Ideally, water should be applied during the season to establish a canopy that can protect bunches from direct exposure. Before the heat arrives, aim to fill the rootzone to field capacity if possible to enable the cooling that occurs when leaves transpire. Postpone any canopy manipulation that may increase bunch/berry exposure. During the heatwave, maintain soil moisture and if using overhead irrigation, apply at night to avoid foliage burn. Also, wind events during heatwaves can result in the canopy rolling and over-exposing the fruit. Look to implement management strategies which can reduce the likelihood of this occurring using foliage wires, etc. After the heatwave, irrigate to replace lost soil moisture and decrease soil temperature. Monitor for pests and disease that may exploit damaged berries.
More detailed information can be found in the GWRDC Innovators Network factsheet: Managing grapevines during heatwaves: http://www.gwrdc.com.au/wp-content/uploads/2012/09/2012-01-FS-Managing-Grapevines-Heatwaves.pdf.
Further assistance
Should you require further assistance, please call the AWRI’s Viticulture, Winemaking and Extension Services team on 08 8313 6600 or contact the AWRI by email.