Pruning trials move into second round

A new season of trials is underway in South Australia as part of an AGWA-funded project investigating the impact of temperature and pruning time on vines, grapes and wine.

Scientists from the South Australian Research and Development Institute (SARDI) are conducting experiments on Barossa Shiraz throughout the 2015 vintage, at both the Nuriootpa Research Centre and in a Treasury Wine Estates vineyard at Marananga.

The aim is to test whether late pruning is a viable option for ‘decompressing’ harvest and maintaining wine quality in the hotter, drier conditions that are likely to prevail in the future.

“We are looking at the effects of pruning the vines in early spring rather than in winter so that flowering and fruit set are delayed and harvest would then coincide with cooler conditions in February,” said SARDI crop scientist Dr Victor Sadras.

The trials during the 2014 vintage produced some promising findings.

In both vineyards, some vines had been pruned the previous winter and others in spring, in both cases at 2-3 unfolded leaves.

At Nuriootpa, pruning time was combined with two thermal treatments – one at ambient temperature and the other at a raised daytime temperature generated using open-top chambers to enclose the vines. Grapes were picked at a targeted total soluble solids (TSS) of 25 °Brix (14 °Baumé), around 12 March 2014.

At Marananga, grapes were picked on the basis of TSS, ripe flavours and tannins; winter-pruned vines were harvested on 4 March and spring-pruned vines on 17 March.

Experimental batches of wine (10 litres of each) were made and tasted at an industry workshop in November 2014. Wines were assessed for 24 attributes divided into six categories (colour, aroma, taste, flavour, body and tannins, and aftertaste).

The panel considered that wines from winter-pruned vines showed more intense colour, bitterness, and earthy and savoury flavours than those from spring-pruned vines when the vines had been grown at ambient temperature, and showed more alcoholic aftertaste when the vines were grown at higher daytime temperatures.

Heated vines pruned in winter produced wines with less colour, more intense red fruit flavours, less body and tannin when compared with wines from current temperature vines. Heated vines pruned in spring produced wines with less colour, black and ripe fruit aromas, saltiness and sweetness when compared with wines from the ambient temperature trials.

At Marananga, it was also noticeable that wines made from winter-pruned vines showed less intense sweetness and ripe flavour but more acidity when compared with those from spring-pruned vines.

“These findings have a seasonal component that requires further evaluation, and that will form a part of trials in 2015 and 2016,” Dr Sadras said.

A second industry workshop will be held later in the year