A project trialling ultraviolet light technology to combat three cherry crop diseases has controlled one disease, significantly reduced another and caused no adverse effects on cherry pollen.
Bioeconomy Science Institute | Plant & Food Research (PFR) conducted the trial, which was funded by A Lighter Touch (ALT) and Summerfruit New Zealand (SNZ). In reporting the trial findings, PFR Senior Scientist Dr Virginia Marroni and Principal Scientist Dr Phil Elmer say the technology shows promise as a new, spray-free, sustainable tool for cherry disease management.
“Results from this initial season were promising, but further research is needed under natural disease pressure conditions to confirm efficacy. A multi-season evaluation will also be important to assess any long-term effects on tree health, yield, and fruit quality.”
Further research would refine the use of UV-C, its role in triggering plant defense responses and its integration into commercial orchard strategies. It would also focus on detailed measurements of yield components, fruit set, fruit number and fruit quality.
An Upright Fruiting Offshoot (UFO) two-dimensional growing system was used in the trial.
The project’s findings, and another UV-C project in grapes involving ALT and programme partner Bragato Research Institute (BRI), are adding to knowledge around UV-C as a new way to control plant diseases for New Zealand crops. The trials have been supported by Agri Automation (NZ) Ltd through the supply of technology, technical expertise and training.
For the summerfruit industry, bacterial and fungal diseases caused by Pseudomonas syringae pv. syringae (Pss), (bacterial canker), Monilinia fructicola (brown rot) and Botrytis cinerea are currently controlled by regular spray applications of bactericides and fungicides.
Duplicate plates of a known concentration of Botrytis cinerea and Monilinia fructicola spores and cells/mL of Pseudomonas syringae pv. syringae set up on poles at the orchard site in Cromwell in 2024. Credit PFR.
Summerfruit New Zealand already has trials underway with A Lighter Touch and PFR looking at efficacy of biological options, as one potential alternative. However, biologicals alone will not be the complete solution for the replacement of synthetic chemistry, prompting an interest in examining the efficacy of UV-C treatment against these diseases.
Results from the cherry trial showed Pss was killed at two light levels (200 and 500 Joules/m2), for brown rot significant reductions of spore germination occurred at both light doses. For botrytis the 500 J/m2 UV-C dose reduced spore viability, while the 200 J/m2 dose had little effect.
The field trial at 45 South Cherries in Cromwell tested the efficacy of UV-C on the Upright Fruiting Offshoot (UFO) two-dimensional growing system, where the trees grow along a trellis system. The UV-C treatment was deployed at night, using the UVEXTM UV-C system coupled with the 100% electric Burro autonomous mobile robot.
Pollen viability was also tested, with laboratory results showing no decline, even at the highest (1000 J/m2) dose. Unprotected pollen showed no decline in viability at 200 J/m2, but did pollen viability declined at higher doses. The results suggest that UV-C at 200 J/m2 could safely be applied during flowering under field conditions.
UV-C treatment being applied in wine grapes as part of the A Lighter Touch-Bragato Research Institute project.
Initial results are also available for the first season of the ALT-BRI project trialling UV-C technology in Sauvignon blanc grapes to control powdery mildew, showing UV-C treatment could halve fungicide applications for powdery mildew.
BRI viticulture research scientist Dr Paul Epee said the results of the first season were “positive and exciting,” showing UV-C light alone or in combination with fungicides can control powdery mildew up until pre-bunch closure on leaves and in bunches at weekly applications of approximately 120J/m2.
“The combination of UV-C light with fungicides – either at three key points in the growing season, or with very light or low environmental impact fungicides like sulphur – can make a big difference and cut down the amount of fungicide by half or more.”
Paul says this project addresses real issues the winegrape industry is currently facing, such as the increased use of fungicides for powdery mildew, estimated at over 1900 tons annually. Spraying excessively endangers the environment and vineyard biodiversity, killing both powdery mildew and beneficial fungi, especially when broad-spectrum fungicides are used.
Growers are also at risk of reduced efficacy of fungicides and resistance development when the same active ingredient is used repeatedly, Paul says. “Therefore, this project offers a non-chemical, more sustainable alternative to divest from synthetic fungicides for the control of powdery mildew in New Zealand vineyards.”
In addition to testing the efficacy of UV-C against powdery mildew, BRI also evaluated its effects on fermentation and wine quality. Further results will be available in the coming months.
Watch a video case study about the project here.
