Hail damage motivated one of the two major vineyard projects currently under way in the Murray Valley region and inadvertently affected the other.
When consultant plant pathologist Dr Bob Emmett started work on a project monitoring a new approach to powdery mildew management, he had to discount one of the six commercial vineyards he planned to work in because it suffered severe hail damage late last year.
Vines damaged by hail
‘The Murray Valley has been hit by hail twice in the last three years’, he said. ‘It does occur from time to time and it’s usually very patchy when it does, but the last one in November was fairly widespread across Sunraysia, hitting wine, dried and table grapes.’
Even severely damaged vines will regrow, but the question is whether growers should prune them back before they do or save time and money by just leaving them. For wine grape vineyards the inclination is to prune, because there is anecdotal evidence that there are benefits in doing so, but this has not been fully tested in Australia until now.
Murray Valley Winegrowers (MVW), with funding support from Wine Australia’s Regional Program and the Victorian Government, commissioned Dr Emmett to run a 30-month trial at Pomona in NSW to compare three approaches: hand pruning with damaged shoots cut back to two-bud spurs, machine hedging, and leaving vines unpruned.
The study is looking at differences in vine canopy regrowth, secondary bunch production and bud fruitfulness in the first season and the effects of pruning practice on shoot, bunch and crop production in the following two seasons.
Early findings were presented at an information day in May, but Dr Emmett expects to have a much clearer picture after harvest at the end of this season. He has been ‘flat out’ collecting data over recent weeks.
The second project, also funded by MVW and Wine Australia, was established to test the theory that ‘less is more’ in relation to spraying and effective, cost-efficient control of powdery mildew.
Growers in the Murray Valley commonly apply more than seven fungicide applications annually for powdery mildew control; in some cases, it is twice that number. However, experience in other regions suggests better results can be achieved with a more refined strategy and a greater focus on ensuring spray machinery is calibrated and set up correctly.
Results from the field trials were very positive, suggesting that good control can be achieved with fewer sprays, while some specific deficiencies in strategies and processes that need to be addressed were also revealed.
The project used an ‘in-vineyard approach’, providing local growers and their neighbours with personalised instruction on what was needed for successful deployment of the revised strategy. Dr Emmett said one important issue was giving people confidence that a reduced and monitored program could consistently prevent disease.
A final report on this project is being prepared for Wine Australia.