Shining new light on fungal disease in grapes

A new project led by Bragato Research Institute in partnership with A Lighter Touch aims to provide another control option for New Zealand winegrowers dealing with powdery mildew in their crops.

Efficiency trial has begun in Marlborough.

Bragato research extension specialist Dr Paul Epee and viticulture technical specialist Chris Ireland say UV-C light technology has been shown overseas to be a cost effective and friendlier option than fungicides, and they’re aiming to demonstrate these benefits in NZ vineyards. 

A key advantage is significant reduction in the use of fungicides, which leads to fewer chemical residues on harvested grapes or juice and wine. 

The technology does not leave harmful residues in the soil or water, and reduces the risk of fungicide resistance, ensuring long-term effectiveness in disease control, they say. 

Further, it enhances worker safety by eliminating the need to handle hazardous chemicals, and also promotes biodiversity by preserving beneficial insects and microorganisms in the agricultural ecosystem. 

“Additionally, UV-C light technology could be cost-effective over time, as the initial setup costs are offset by reduced chemical purchases and improved crop yields.”

UV stands for Ultraviolet, and C describes the wavelength. 

UV-A, UV-B, and UV-C lights have wavelengths of 315-400, 280-315, and 180-280 nanometres, respectively.

UV-C light has a germicidal effect that disrupts the DNA and cellular structures of pathogens such as fungi, bacteria, and viruses, reducing plant disease severity, Epee and Ireland say.  

“Research has demonstrated that UV-C light can directly harm plant pathogens and stimulate the plants’ natural defence mechanisms, making them more resistant to diseases.”

This dual action of UV-C light not only helps in controlling diseases but also enhances the overall health of the plants.

The UV-C treatment is most effective when applied at night, because fungi have the ability to repair the damage that UV light causes using the blue and UV-A components of sunlight. 

“Recent technological developments in UV-C light, as well as development in autonomous machines, like the one supplied for this trial by Agri-Automation, has allowed this technology to become more accessible to winegrowers.”

The new research project has two objectives – to test the efficacy of the UV-C light technology to demonstrate and establish its performance in fighting powdery mildew on Sauvignon blanc and its effects on fermentation and wine quality; and to develop grower resources that will support effective change in vineyard practice and management to meet economic and sustainability goals.

An efficacy trial on sauvignon blanc has been established in Marlborough in conjunction with Whitehaven Wines and will be monitored over two growing seasons, from budburst through harvest, to assess the performance of the technology for control of powdery mildew against a standard spray programme.

The results of the efficacy trials, along with the winemaking, aroma, and sensory analyses completed in the second year, will be presented and accessible to growers to guide their decision-making about adopting this new technology. 

Cost-benefit assessments will be conducted for the technology.

“This project aims to deliver robust, local knowledge, giving growers comprehensive and objective data so they can make informed decisions. 

“If UV-C is shown to deliver on the potential it indicates, growers will have the know-how and confidence to use this new approach to deliver productivity and sustainability gains.”

If the technology is widely adopted, equipment suppliers would also benefit, Epee and Ireland say.  

BRI will use commercially available equipment to conduct the trials, focusing on the interactions between UV light, the plant, and the fungus. 

Data will be reported based on the treatments applied, such as light intensity, energy, groundspeed, and timing, without endorsing any specific equipment make/brand or configuration. 

This approach will encourage multiple suppliers to offer machines capable of delivering the reported treatments, fostering competition and benefitting the industry.