Let bushfire-damaged vines recover through to winter, rather than take immediate action.
That is the message from Richard Hamilton of Hamilton Viticulture – one of the many viticulturists, growers, winemakers and volunteers who offered timely and valuable help following the devastating Adelaide Hills bushfires in the summer of 2019–20.
The fire broke out in Cudlee Creek in catastrophic fire conditions on 20 December 2019 and then quickly spread through parts of the Adelaide Hills region. Homes, outbuildings, livestock, pets and crops – including some vineyards – suffered fire damage.
Richard recalls that the damage was ‘horrendous’, coming after days of continuous high temperatures.
‘Growth of vines within a vineyard is influenced by a range of integrated factors including soil type, soil depth, aspect and altitude. As a result, vine growth within vineyards has a wide range of variability’, Richard said.
‘Bushfires are highly unpredictable and are influenced by factors including wind direction and speed as well as slope and aspect in the vineyard. The concern for the vines impacted by this bushfire was that not only had their foliage been scorched, but their trunks had been damaged by heat affecting their xylem, phloem and cambium – the “hose pipes” that supply water and food.
‘However, vines are remarkably resilient and while the above ground part of the vine may be damaged and scorched, the deep root system may be unaffected.’
It was on this premise that growers were advised to examine the cambial layers by shaving the trunks of selected vines in the days and weeks following the fires to see if the cambium layer was still alive (green). The cambium is a tissue layer under the bark of a vine that provides cells for plant growth. It is found in between the xylem and phloem and is a good indicator if the vine’s ‘hose pipes’ are damaged.
‘However, we found that this was not a reliable way of predicting damage to the vine’, Richard said.
The question then was whether to let the vines recover in their own time, or cut them back immediately after the bushfire to encourage rejuvenation.
Richard and his team have been trialling both options with some interesting results.
‘In the first trial we beheaded the vines within two weeks of the bushfire damage, and then compared them with vines beheaded once vines become dormant in the following winter (June).'
The second trial applied three pruning treatments during the winter after the fires: beheading, cane pruning and spur pruning.
Richard said the findings – which he will outline in his presentation at the National Wine Sector Bushfire Conference on May 25 – are important.
‘Without giving too much away, we can say that the preferred option is to take a “wait and see approach” after a fire, and then make pruning decisions in winter.’