As winter pruning approaches, growers should be aware of the high risk of wound infection by trunk disease pathogens.
“Wounds are most susceptible to infection in the two weeks after pruning – particularly immediately after cuts are made and during periods of rainfall,” said Dr Mark Sosnowski, senior research scientist at the South Australian Research and Development Institute (SARDI), the research arm of the Department of Primary Industries and Regions (PIRSA), and author of the Grapevine Trunk Disease Best Practice Management Guide, funded by Wine Australia.
Eutypa dieback (eutypa) and botryosphaeria dieback (botryosphaeria) are the most common grapevine trunk diseases.
The diseases are caused by fungi that are spread by airborne spores. The spores are released from fruiting bodies on dead wood during periods of rainfall, and can infect pruning wounds. The fungus then progressively kills spurs, cordons and trunks of the vine. In the case of Eutypa lata, shoots become stunted and leaves become yellow and distorted.
“It is important to protect all wounds on younger vines less than 20 years old showing little or no symptoms of dieback, particularly during and after periods of rainfall,” said Dr Sosnowski.
He said in canes that are 1–2 years old, grapevine trunk disease pathogens have been observed to advance by as much as 20cm in a year. In older wood of cordons and trunks, it could advance up to 8cm a year.
What to look for
Foliar symptoms – including die back and ‘cankers’ on spurs, cordons and trunks – are most obvious in spring, when shoots are 30–70cm long.
Alternatively, growers can dissect the cordon or trunk to reveal wedge-shaped or central staining.
If eutypa or botryosphaeria is suspected, growers can send samples for testing to their local diagnostic laboratory.
Quick tip: The Grape Assess smartphone app can make monitoring grapevine trunk disease quicker and easier. The app can be downloaded free from the Android and Apple app stores.
How to control the disease
Disease control can be achieved using wound treatments and remedial surgery.
Preventative wound treatments can be applied post-pruning to reduce the likelihood of new infections.
“For older, infected vines, assess the progression of internal staining in trunks and consider remedial surgery to regrow shoots from clean wood,” he said.
Top tips for growers:
- Vines showing foliar and dieback symptoms of eutypa or botryosphaeria should be tagged in spring when symptoms are most obvious. The vineyard manager can then easily return to the same vine even if the symptoms are no longer obvious.
- Infected wood can be removed at any time of the year and burnt or buried. If removed from the vineyard, the infected wood should be securely transported and disposed of to prevent the spread of disease.
- Any discoloured cordon and trunk should be cut out – along with an additional 20cm of cordon or trunk to ensure all infected wood has been removed. The lower the cuts are made on trunks, the greater the likelihood of eradicating the pathogen from the vine.
The Grapevine Trunk Disease Best Practice Management Guide is available here. The guide includes an invaluable ‘decision tree’ for developing a remedial management plan for vines affected with trunk disease.