The potential impact of fungicides on the micro-organisms that exist on the surface of grapevines and the flow-on effect on the sensory outcome of wines has been explored as part of a PhD project funded under Wine Australia’s research scholarship program.
With the growing volume of evidence showing how antibiotics can have negative effects on the microorganisms in the human gut, University of Adelaide PhD student Brady Welsh was keen to determine whether common anti-fungal sprays were having a similar effect on the microbiome of grapevines given that they target cellular systems shared by many different fungal species and certain bacteria.
“Our understanding from previous research shows that a rich microbiome is closely related to a healthier vine which is also important in the context of spontaneous fermentations,” Welsh says.
He began his investigations by looking into the effects of copper and sulphur in particular on the structure of the microorganism communities in potted Shiraz in a semi-controlled environment.
Although the results showed that the copper and sulphur-based fungicides had little to no effect on the structure of the microbial communities, there was evidence that the spraying process, and repeated spraying, could lead to rapid decreases in the diversity within those communities. This lack of diversity could have implications further down the line during the winemaking process.
Welsh then extended his research to look at the effects of fungicide regimes in three vineyards with different types of disease management - conventional, organic and biodynamic. This stage also included tracking the vineyard results through the winemaking process.
“I collected grape samples from each vineyard and made them into wine using identical techniques, the only difference being whether the fermentation was spontaneous or inoculated,” Welsh explained. “These wines were then subjected to chemical and sensory analyses. Microbial samples were also taken at various stages of the fermentation process which enabled me to compare those microbial results with the sensory results from the final wines.
“There was a clear association between the richness of microbial populations and distinct characteristics in the resulting wines.
“These results were quite clearly linked to the management methods that were being used in each vineyard.
The low-input, organic vines had significantly more diverse microbial populations, which correlated with what I saw in my potted vine trials. I also saw a distinct sensory profile in those wines, as opposed to the other high-input vineyards which seemed to make wines with similar sensory profiles across the wild and inoculated fermentations.
“There was a lot more fruity flavours in the organic wines, whereas we saw more acidity, and astringency in the conventional and biodynamic wines. This could be due to the presence of more spoilage organisms in the higher-input vines which were able to outcompete what little microbes were present on the vines, especially in the case of the spontaneous ferments.”
Welsh said his research highlighted the potential to optimise spraying practices to preserve and utilise the grapevine microbiome, especially in wild fermentation scenarios.