Trials of UV-C light treatment for fungal and bacterial disease control in cherries shows the technology has potential as a sustainable tool for growers.
The Summerfruit New Zealand-A Lighter Touch project is in its second year, evaluating UV light as an alternative control for diseases such as Monilinia fruticola (brown rot), Botrytis cinerea and Pseudomonas syringae (bacterial canker).
Undertaken this past season by the Bioeconomy Science Institute (BSI) at Cromwell cherry orchard 45 South, the second year of trials involved a split-plot design with one row receiving 15 UV-C treatments throughout the season, and a control row that received none. For each row, five plots of three trees were assessed for yield, disease control efficacy, and phytotoxicity (plant health).
UV-C light trial at night in Cromwell. Credit: Rusty Davidson
For disease control, pre-harvest bacterial canker leaf spot was significantly reduced in the UVC treatment and there were no other fungal rots present pre-harvest.
Fruit samples were taken at harvest and incubated for eight days to assess disease expression. For export grade fruit, the UV-C treatment significantly reduced the mean number of infected fruit with Alternaria spp. and Penicillium spp. by more than 80 per cent. The incidence of Botrytis on export grade fruit was low and no difference between treatments was observed. For domestic grade fruit, the same trend for reduced fungal disease incidence on UV-C treated fruit was seen.
Post harvest fungal rots due to Alternaria spp. and Botrytis in reject fruit were similar in both the UV-C treated and control plots.
The second year trial supported the previous year’s findings, and the UV-C treatment did not negatively impact pollen viability.
The Burro autonomous robot used to deploy the UV-C light technology. Credit: Rusty Davidson
The UV-C treatment, deployed at 200 joules/m2 had an unexpected positive effect on yield. It significantly increased both the average gross yield per tree (by 82 per cent) and the total number of fruit per tree (by 76 per cent). Average cherry weight was similar for the untreated control and the UV-C treated plot and there was no difference in fruit quality. The increase in fruit number shows there is unlikely to be a negative effect on yield from UV-C treatments but further validation is needed to confirm whether UV-C could improve fruitset.
This past season’s trials used the same technology from the 2024-25 trials in the form of UVEX UV-C light technology deployed at night using a Burro autonomous mobile robot, under natural field conditions. Agrichemical sprays were excluded from the UV-C and control rows in this trial.
The results from this year’s trial combined with previous work show that UV-C is a promising technology for fungal and bacterial disease control in cherry. Further work is required under higher disease pressure and at larger scale to validate its performance.
Learn more about the first season results and watch a video of the UV-C being deployed on the project page of the ALT website or tune into the Summerfruit NZ’s Lunch and Learn webinar on 20 August, 12:30-1:00 PM (see www.summerfruitnz.co.nz for details).
