Results from the national project aiming to improve trunk disease management for vineyard longevity have provided important insights into optimum pruning times.
“We’ve made huge inroads into wound protection, which is the number one management strategy with trunk diseases,” said project leader Dr Mark Sosnowski from the Department of Primary Industries and Regions research division South Australian Research and Development Institute (SARDI).
Field trials established in the Adelaide Hills revealed that wounds were highly susceptible to eutypa and botryosphaeria dieback pathogens immediately following pruning, after which the susceptibility decreased rapidly over the following 14 days.
“From 21 days post-pruning, susceptibility was generally negligible. This indicates that wounds are most vulnerable to infection for the first 14 days following pruning, similar to that reported in earlier trials in McLaren Vale,” Dr Sosnowski said.
For the eutypa pathogen, wounds were generally most susceptible to infection when pruned in early June and least susceptible when pruned in late August.
“Therefore, in the Adelaide Hills, there may be an advantage in delaying pruning to later in the dormant season to minimise risk of infection, as was also the case in McLaren Vale.”
The research team found that susceptibility of wounds to the botryosphaeria pathogen did not vary greatly between pruning times. “So there appears to be no real advantage in avoiding the early pruning time,” Dr Sosnowski said.
“However, there was minimal natural infection of pruning wounds by the botryosphaeria pathogen, indicating a low presence of this pathogen in this vineyard. Future research should focus on the extremes, cool and hot-wet climate regions in order to ascertain if the periods of greatest wound susceptibility vary from that of the more moderate climate regions.”
With regard to wound protection, previous fungicide timing trials indicated that eutypa and botryosphaeria pathogens are controlled when wounds are treated with fungicide up to six days after infection and will continue to provide control of both pathogens for 1-2 weeks.
“Therefore, a single application of a registered fungicide could provide up to three weeks of wound protection, which covers the most susceptible period of 14 days post-pruning, as shown in the current research,” Dr Sosnowski said.
In wound spray coverage trials conducted in McLaren Vale, the research team found there is no benefit in adding adjuvants (wetters and stickers) to increase coverage and improve efficacy of registered fungicides in preventing eutypa infection.
A low water rate (200 L/ha) was purposely used to provide sub-optimal coverage of pruning wounds to test the ability of adjuvants to increase coverage and efficacy. This led to poor disease control, reiterating the importance of applying the recommended minimum water rate of 600 L/ha to achieve sufficient coverage.
“This is a very important point,” Dr Sosnowski said. “Unlike with downy or powdery mildew where you know quickly if you don’t get your sprays right, with trunk diseases, you don’t see the results of your sprays for 5-10 years, so it’s easy for growers to be complacent. But this work has shown that it’s critical to get the spray rates right and spray at the right times.”
The project team has also examined the effectiveness of biological controls and organic products for trunk disease management. To date, no alternative products have offered protection equivalent to that of fungicides and paints.
“Unfortunately, pruning wound infections are pretty hard to stop, as wounds are severe and take time to naturally heal and protect from infection. For the two weeks that they are healing, without any added protection, they are an open portal for pathogens to enter and infect the wood,” Dr Sosnowski said.
“But the search continues to look for an effective biocontrol for trunk disease management.”
This ongoing work is part of a five year project called ‘Grapevine trunk disease management for vineyard longevity in diverse climates of Australia’, funded by Wine Australia. Based in South Australia, Dr Sosnowski leads a team consisting of Mr Matthew Ayres (SARDI), and based in New South Wales, Associate Professor Sandra Savocchia and Dr Regina Billones-Baaijens (Charles Sturt University and National Wine and Grape Industry Centre).