Stepping up the fight against grapevine trunk disease
Dr Mark Sosnowski has been studying Eutypa for 14 years and says there’s still a lot more to be done. Fortunately, he enjoys the work and believes that ‘we’re hitting some home runs now’.
‘Very little was known about it up until 15 years ago and it takes a long time to get results because the disease progresses very slowly’, he said. ‘It can take 8 to 10 years from infection for obvious symptoms to show up in the vineyard.
‘We started working just on Eutypa dieback but that has expanded to include Botryosphaeria dieback because we’ve come to realise that it’s just as big a problem in this country and that they work pretty much together and in the same way.’
Both were the focus of a recently completed three-year project, funded by Wine Australia, that Dr Sosnowski carried out with colleagues at the South Australian Research and Development Institute*, in collaboration with the National Wine and Grape Industry Centre and the University of Adelaide. It included six different but complementary components.
The clearest and most surprising result was that, contrary to common belief, water stress caused by drought or regulated irrigation does not exacerbate disease. Quite the opposite in fact.
‘We really stressed the vines, but then when we inoculated them with Eutypa or Botryosphaeria the rate at which pathogens colonised the wood and caused dieback did not increase; with Eutypa it actually slowed significantly’, Dr Sosnowski said.
‘That wasn’t what we expected but when you think about it, it makes sense, because our variety susceptibility research has shown that the physical size of the canes affects how quickly the fungus can move through it. The take-home message is that it may not be stress that’s causing the problem; we just need to be more vigilant about managing the disease.’
Getting a clearer idea of how to do that was central to the recent project, as it is to further research already under way.
The principles of control strategies are pretty straight forward – protecting pruning wounds and removing the infection that’s already there – but there is a real focus on fine-tuning management strategies, particularly around wound protection to ‘make sure that we’re applying wound protection at the right time and only when it’s necessary’.
The first issue is when to act. The recent project confirmed that rainfall is the primary factor that triggers the release of spores, but there are other environmental factors at play that require further study, and release patterns vary between regions and across the year.
‘Spore release mainly happens during winter but it can happen at any time of year so we need a clearer picture of the pattern in different regions’, Dr Sosnowski said. ‘We need to determine the risk of infection during spring and summer shoot trimming and thinning activities.’
The second issue is the nature and timing of the response. Trials in McLaren Vale and Wagga Wagga suggest there is little advantage in choosing one pruning time over another, but that wounds are most susceptible to disease pathogens in the two weeks immediately following pruning – whenever it takes place.
On the upside, fungicides provided wound protection for up to three weeks, meaning that a single application should be sufficient if applied at the right time.
‘The aim is to get better at predicting spore release so growers will know whether spores were active on a given day and can make informed decisions about how long they’ve got before spray needs to be applied’
‘If we can bring all three aspects together growers will have a lot more confidence in predicting when to protect vine wounds and when they don’t need to.’
Another component of the project looked at whether remedial surgery, which has been shown to control Eutypa dieback, can also be effective with Botryosphaeria. That’s still very much a work in progress, but the researchers did note difficulties with renewing shoots from the scion when working with grafted vines.
‘It’s a limitation that we’re considering in our new project, to see if there’s something we can do, such as top-working. But there may be other things we can do, which we’re trialling now.’
* SARDI is a division of Primary Industries and Regions SA (PIRSA).