Fires and smoke taint
Fires and smoke exposure experienced in New South Wales in October have caused some grape producers to become concerned about the possibility of smoke taint issues. It’s important to remember that the sensitivity of wine grape varieties to smoke uptake depends on the grapevine growth stage. In general, the smoke uptake potential is low through flowering up to the point when the berries are pea size. At this stage, the potential becomes variable (low to medium risk of smoke uptake) and remains variable through the onset of veraison up to three days post veraison. From seven days post-veraison, most wine grape varieties are highly sensitive to smoke taint.
While the above risk assessments are true in general terms, there are many grape varieties that have not been individually assessed for their smoke uptake potential at the various grapevine growth stages. Consequently, if a vineyard has been exposed to smoke sometime after the point when the berries are pea size, it is advisable to sample the vineyard two weeks prior to the harvest date and conduct a small-lot ferment. The wine resulting from this small-lot fermentation can be subjected to sensory assessment and chemical analysis in order to gauge the potential risk of any smoke taint that might arise from the smoke exposure.
Frost events during October have resulted in significant damage to grapevines across many wine growing regions throughout Australia. Lower than average late winter and early spring rainfalls have made many of these growing regions more susceptible to frost events. Notably frost events around 14, 15, 18 and 25 October resulted in the most significant damage in many growing regions, particularly Riverina, Canberra, Tumbarumba and Rutherglen. Frost at these times can kill the foliage right back to the cordon or partially kill the shoots and inflorescences, resulting in significant crop losses. The frosts appear to have affected varieties to differing degrees. The most significant damage appears to have been observed in the later ripening varieties such as Cabernet Sauvignon and Shiraz. Assessing crop losses after a frost event can be difficult, as vines are able to respond through the growth of secondary buds and via other grapevine yield compensation responses (e.g. improved fruit set and increased berry growth). Depending on the timing and severity of the frost, growers may consider a range of management options to improve yield in the current and subsequent seasons, as well as providing good quality canes and spur positions for pruning in the following winter.
A webinar titled Managing frost in the vineyard will be held on Wednesday 20 November at 11:30am (Australian Central Daylight Time). Sonja Needs from the University of Melbourne will present strategies to improve your vineyard’s ability to withstand frost and what to do after a frost event. To register, please visit the AWRI website.
The AWRI offers a free and confidential help desk service on technical issues, to all Australian grapegrowers and wine producers. Should you require further assistance, please call the AWRI’s Winemaking and Extension Services team on 08 8313 6600 or email: firstname.lastname@example.org.