There’s more to trunk disease than meets the eye

Controlling grapevine trunk disease is a pretty simple concept but you have to know a lot of things to do it in the best way and with the least amount of resources.

That reality has underpinned more than a decade of research at the South Australian Research & Development Institute (SARDI), with funding by Wine Australia, which considers it a high priority for the sector.

Current research, led by Dr Mark Sosnowski at SARDI, a division of Primary Industries and Regions SA, in collaboration with the National Wine and Grape Industry Centre and the University of Adelaide, is investigating whether the same practices can be used to manage the two different diseases that cause dieback in grapevines – Eutypa and Botryosphaeria (colloquially known as Bot).

A new three-and-a-half year project beginning next January will take the research further, updating data, ensuring strategies developed are effective for the two diseases, and investigating whether things should be done in certain ways under certain conditions.

Eutypa and Botryosphaeria have similar epidemiology and work in essentially the same way. Fungal spores infect pruning wounds and if not stopped slowly colonise the wood, causing dieback and eventually death. Different fungi are responsible, but they are related.

The major differences are that you see foliar symptoms before dieback in Eutypa (and thus get some warning) but not in Botryosphaeria, and Eutypa is primarily found in cooler regions.

‘If you draw a line from Orange in NSW to Clare in SA, everything above it will only be Bot whereas below it you get both, with Eutypa becoming more and more common the further south you go’, Dr Sosnowski said.

With either disease, the way to stop the infection is to apply fungicides directly to the wound, but there are a number of variables – and things do change.

Dr Sosnowski said the research program was ‘looking at a lot of different angles’.

‘We continue to examine management strategies, which is prevention of infection and timing of the application; after pruning how long have you got to get your protectants on and how long do they last for?

‘We are also learning about the susceptibility of the wounds following pruning; without putting anything on them wounds will heal themselves, but it takes some time. So we are looking at how long they are susceptible at different times of the season.

‘The other thing we are looking at is spore dispersal. We are developing methods of spore trapping, and are about to really intensify that in the next project, when we’ll be trying to understand when spores are present exactly and give a clearer picture to growers about when they need to be protecting their wounds, based on spore dispersal.’

The current body of knowledge about Eutypa is being consolidated in a Best Practice Manual, which Dr Sosnowski will have finished and available on the Wine Australia website in the middle of the year.

He also features in an introductory video on trunk disease management funded by the SA Central region (covering McLaren Vale, Adelaide Hills and Langhorne Creek), which can be viewed on the Wine Australia website. One of his key messages is to take a ‘prevention rather than cure’ approach.

‘If you start protecting vines from first year you prune the vineyard the likelihood of having major disease issues in 10 to 20 years’ time will be very low’, he said. ‘It’s pretty much an insurance policy to apply one post-pruning spray per year.