Wine Australia is funding a new project to learn more about fungicide resistance in Australian vineyards. In the meantime, the best advice for viticulturists is to stick to the published resistance management strategies.
‘If you are at all in doubt, minimise the use of the fungicide you think you’ve got a problem with; and use an alternative,’ said pathologist Barbara Hall.
‘If you think you’re having a problem with DMIs, don’t keep using the same DMI, because there are differences between them. You may have bought a great big container you want to get through, but continuing to use it may not be a good economic decision if it’s not working well and you suspect resistance.’
Mrs Hall – a Senior Research Scientist with the South Australian Research and Development Institute, a division of Primary Industries and Regions SA – led a recently completed project that highlighted the incidence and severity of resistant fungal populations of the big three major vineyard diseases – powdery mildew, downy mildew and botrytis.
The project also involved specialists from the Australian Wine Research Institute, Curtin University, the University of Adelaide, the National Wine and Grape Industry Centre and the WA Department of Agriculture and Food. Many of the same collaborators will be involved with the follow-up project, which Mrs Hall will also lead.
‘What we’re looking at particularly is trying to understand the relationship between the laboratory testing and field performance,’ she said. ‘How does lab testing relate to whether you’re going to see a reduction in field efficacy with the fungicides?
‘We know resistance is out there and we know anecdotally that people have had field failure in certain areas, but there is a whole raft of things that can cause field failure, not just resistance.’
‘Before you blame fungicide resistance on loss of efficacy, you really need to look at your spray application,’ she said. ‘Are you driving too fast? Are you not putting the chemical on properly? Have you checked what coverage you’re getting?
‘You need to have your sprayer set up properly. You need to be targeting the right part of the vine. And you need to get the right coverage. If you’ve got too much leaf and you’re trying to target the bunches, you might not be getting the spray where you want it.’
The advice to start a fungicide program with a multi-site is equally important.
‘If you want to deal with powdery, for example, start your program with a fungicide that attacks a multi-site such as a sulfur rather than your single-mode-of-action ones. If you’ve got a well-established infection, using a single-site mode of action increases the risk of resistance developing. If you’ve got an established infection, you really need to try to control it before you start putting on single-site action fungicides.’
And if you need more advice? ‘Start off with your local chemical reseller. Talk to the agronomist. Talk to your winery technical people or your local Department of Agriculture viticulture adviser.’
For more information, see Crop Life Australia’s chemical resistance management strategies in the AWRI’s agrochemicals booklet (dog book).
 Demethylation inhibitor (DMI)