At a commercial level, an Italian company is utilizing ozonated water to spray vineyards as a means of disease control that leaves no chemical residues and allows for short re-entry intervals.

According to information published on the OXIR website, 14 vineyard trials conducted over a period of two years have shown that the use of ozone treatments resulted in a reduction in the severity and incidence of downy mildew, with reductions ranging from 11% to 65% when compared to an untreated control group.

The project has garnered the interest of researchers who have previously attempted similar approaches in America, but were unsuccessful. However, some skepticism remains among these researchers.

Matthew Grieshop, who currently serves as the director of the Grimm Family Center for Organic Production and Research at California Polytechnic State University and previously worked as an entomologist at Michigan State University, has conducted laboratory and field trials with ozone generators. Commenting on the Italian company’s use of ozone treatments, Grieshop noted that “they’re putting data out there” and acknowledged the value of the information.

Ozone technology provides effective control of fungal and bacterial pathogens in indoor settings such as food packing, preparation, and controlled-atmosphere fruit storage. This method leaves behind no chemical residues and requires only a short re-entry interval of a few minutes.

Although ozone technology has proven effective in controlling pathogens in indoor settings, independent trials conducted by Matthew Grieshop and Lav Khot of Washington State University revealed that using ozone from a sprayer was ineffective in fighting pathogens in vineyards and apple orchards. The ozone consistently broke down into oxygen by the time it reached the plant, and Grieshop had difficulty maintaining even 1 part per million in the tank, let alone in the spray mist.

According to the leaders of the OXIR project, they are able to deliver between 3 and 4 parts per million of ozone at the point of vegetative contact, which is sufficient to reduce diseases without causing any harm to the plants (i.e., phytotoxicity).

Khot, an agricultural engineer, described the development as “encouraging for sure.”

Experience in Italian

MET Srl, an ozone company, and G.R. Gamberini, a farm equipment supplier based near Bologna, partnered to create OXIR using a Horizon 2020 grant from the European Union research and innovation funding program. The partnership currently has approximately 50 service clients in Italy, including both greenhouses and outdoor fields. Among the outdoor fields, eight are vineyards.

According to Francesca Ponti, a scientific support representative for OXIR, the most effective results in the downy mildew trials were achieved when operators followed the ozone treatments with Kocide, a copper-based fungicide and bactericide that is registered in the U.S. for organic use.

Francesca Ponti stated that the trials were carried out at 10 different experimental sites located in Italy, Spain, Morocco, and Oregon (in the U.S.). The trial results were collected and tabulated by Agri 2000 Net, a private research laboratory in Bologna.

According to Ponti, OXIR is able to achieve even better results for its commercial clients by adding zeolites, which are aluminosilicate minerals used as a catalyst.

Although the trial figures appear promising, Grieshop remains doubtful of ozone’s effectiveness in outdoor settings. He believes that one of ozone’s major advantages, its lack of residue, is also a disadvantage. This is because ozone only kills pathogens at the time of application and does not provide long-term protection. As a result, if the pathogen is still present in the environment, it can easily reinfect the plant.

Grieshop explained that “It’s the same reason why we perform surgeries in a sterilized room rather than a barn.”

OXIR is aware of this issue and has tested the use of ozone in a sunflower oil emulsion in an attempt to prolong its effectiveness for eight to 10 days after application. While this approach sometimes produced better results than using ozone alone, it was not always effective.

Khot and Grieshop have expressed the need for laboratory trial results. For instance, Khot’s team did not attempt to mix ozone with oil, and therefore, he believes that additional exploration is required to understand why and the mode of action.

According to Grieshop, laboratory work would provide dose and response curves that would be useful in understanding the potential of ozone spraying. He believes that ozone spraying would be more valuable in enclosed environments such as greenhouses. However, Grieshop acknowledges that OXIR’s data is promising and is a step in the right direction.

Grieshop expressed his desire that ozone spraying will work.