Do fungicides in the vineyard affect wine quality?
Spraying for fungicides is a crucial viticultural practice that occurs throughout the growing season. But 'does it have an impact on wine quality?' asks University of Adelaide wine researcher Natalia Caliani.
It’s a sunny Sunday morning. You’re driving through the rolling hills of one of South Australia’s magnificent wine regions. There is perfectly manicured, green and lush grapevines as far as the eye can see.
Suddenly, a monster-looking machine appears on the scene and disrupts the tranquil drive: what is it doing? You might be looking at a fungicide sprayer.
Looking like something from the TV show Stranger Things, a tractor pulls a spray unit across this Adelaide Hills vineyard.
Fruit crops are susceptible to many unwanted fungi that can cause disease. Just take a look in your fruit bowl and you might see some fungi there.
Grape growers spray fungicides, a specific type of pesticide to inhibit or kill fungi that can cause disease. It is a crucial viticultural practice that occurs throughout the growing season to help protect both the vines and developing grape bunches. Growers will adjust the amount that they spray based on the season's weather and, might spray less if it is hot and dry or more if it is wet and rainy.
It is generally agreed that fungicides are sprayed to kill the harmful fungi; however, they can also kill beneficial organisms living on those vines and bunches, known as yeast.
These tiny creatures we cannot see with the naked eye are micro-fungi and are related to the microorganisms that cause disease. However, these yeasts can also be beneficial and may play an important role in the wine industry.
Yeasts transform sugar in grape juice into ethanol and carbon dioxide. In the case of ‘wild’ wines, native yeast - those coming from the vineyard - are the only microorganisms that will ferment the grape juice, transforming it into wine.
Native yeasts will also contribute to different wine sensory attributes such as mouthfeel, texture, length and aroma profile. Fermentation performed by more diverse yeast communities might boost these sensory attributes.
There are many different fungicides and they all do something different to disease-causing fungi. Just like your doctor has a wide range of drugs to choose from to treat human diseases, a viticulturist will treat grapevines with different fungicides depending on what they consider the most appropriate.
The products used may also affect yeast communities differently. Let's think about how our environment affects our health and wellbeing: the water we drink, the food we eat and the air quality for example can have big impacts on how we feel.
In that same way, the environment where these yeasts are growing - and what they consume - will also impact their growth and health. Consequently, we need to know which fungicides have a detrimental impact on yeast and their environment, so viticulturists can choose other options when managing diseases, and minimise the negative effect on beneficial native yeast.
Grape expectations
My research is based at the University of Adelaide’s School of Agriculture, Food and Wine. I am undertaking fieldwork at an Eden Valley vineyard to better understand how different fungicides affect the indigenous yeast found on grapes.
To do this I am comparing grapes from two different blocks. These two blocks are similar apart from their disease management treatments, either using conventional or biodynamic treatments.
The biodynamic block is only sprayed with copper, sulphur and biodynamic preparations such as horn manure and horn silica. The conventional block is sprayed with copper, sulphur and a range of synthetic products.
The grapes I harvested in the first season have been crushed to juice, which was used to run uninoculated (‘wild’) fermentations. Both uninoculated conventional and biodynamic fermentations were sampled at multiple time points to profile what yeast were present in the beginning and how the yeast communities evolved as fermentations progressed.
We will repeat this trial in the coming season, along with a separate experiment with potted vines that have been sprayed with different fungicides or only water (as a control). You will need to wait for a bit before you can read about the results.
Ultimately, this type of information will let both viticulturists and winemakers decide how to harmoniously manage the vineyard and the winery. It will help us to understand how fungicides in the vineyard affect wine quality and develop strategies to look after the good yeast.
About the author: Natalia Caliani
The growing interest in more interesting and innovative wine production has led us to investigate wild yeast populations found on grape surfaces. These species known as non-Saccharomyces, seem very promising as they can contribute to improving aromas and global perception of wine.
However, there are still many aspects of their metabolism that we do not know. My research aims to investigate their resistance to different wine stressors such as fungicides, ethanol and sulphur dioxide; and then determine how they could be used to benefit the wine industry.
Natalia acknowledges her PhD supervisors, the Australian Research Council Training Centre for Innovative Wine Production, the centre’s industry partners and Yalumba winery for their contributions to the project.