Phytotoxicity of Aqueous Ozone on Five Container-grown Nursery Species

Abstract

<jats:p>The phytotoxic threshold of five woody perennial nursery crops to applications of aqueous ozone was investigated to determine if aqueous ozone could be used for remediation of recycled nursery irrigation water and for pathogen control. The perennial nursery crops [<jats:italic>Salix integra</jats:italic> Thunb. ‘Hakura Nishiki’; <jats:italic>Weigela florida</jats:italic> Thunb. ‘Alexandra’; <jats:italic>Spiraea japonica</jats:italic> L.f. ‘Goldmound’; <jats:italic>Hydrangea paniculata</jats:italic> Seib. ‘Grandiflora’; <jats:italic>Physocarpus opulifolius</jats:italic> L. Maxim. ‘Summer Wine’] were evaluated for aqueous ozone phytotoxicity after 6 weeks of overhead spray irrigation in which five aqueous ozone treatments (0, 10.4, 31.2, 62.5, 125.0 μmol·L<jats:sup>−1</jats:sup>) were applied on a daily basis. The concentrations applied represent levels useful for irrigation system maintenance (pathogen and biofilm control) with the highest levels selected to clearly demonstrate phytotoxicity. Aqueous ozone solutions were prepared and injected in-line during irrigation for 7.5 min every day for 6 weeks, after which growth parameters (leaf area, shoot dry weight, root dry weight, height, flower number) were measured and leaf injury was evaluated. High residual aqueous ozone (62.5 μmol·L<jats:sup>−1</jats:sup> or greater at emitter discharge; 0.3 m from canopy) in the irrigation water was shown to negatively affect the growth parameters measured; however, low residual ozone concentrations (31.2 μmol·L<jats:sup>−1</jats:sup> or less at emitter discharge; 0.3 m from canopy) did not present any measurable risk to plant growth. Furthermore, even at higher dose levels, leaves produced during the treatment period showed reduced damage levels. It is concluded that ozone residuals of 31.2 μmol·L<jats:sup>−1</jats:sup> (at emitter discharge) can remain in overhead irrigation water without negatively affecting the crop species examined under the application protocols used. At the ozone concentrations demonstrated to be tolerable by the crop species examined, it is reasonable to surmise that control of pathogens at all points within the irrigation system will be achievable using aqueous ozone as part of an irrigation management strategy. The use of aqueous ozone in this fashion could also aid in dramatically reducing chemical residuals on crops by reducing the input requirements of traditional chemical controls.</jats:p>

Characterizing the Phytotoxic Effects of Hydrogen Peroxide on Common Microgreen Species and Lettuce Cultivars

“…The variability in DI values suggests an opportunity exists to misidentify DI 1 or 2 compared with DI 3 or 4 values when investigating H 2 O 2 damage among multiple crops. Further, computer software, normally used to quantify foliar damage (Graham et al, 2009;James, 1971), could not be applied as H 2 O 2 damage was not distinctive enough to be recognized by software for any of the affected crops. Quantifying the percentage of damaged leaves per tray, along with the DI of individual leaves, provides a more accurate measure of H 2 O 2 leaf damage.…”

Liverwort Control: An Ancillary Role for Ozone-based Irrigation Water Treatment Systems?

“…Expt. 3 was designed to evaluate liverwort response to application frequency at CTs previously determined to be acceptable for woody perennial production (Graham et al, 2009).…”

“…This study has focused on aqueous ozone [O 3(aq) ] (in the context of this study, aqueous ozone refers to water that retains a residual ozone concentration) as a potential component of an overall liverwort management program when the technology (ozonation system) is already used as an irrigation water remediation tool. Aqueous ozone has a long history of water and wastewater treatment applications and in recent years has also gained some momentum as an irrigation water treatment technology in nursery and greenhouse production (Ehret et al, 2001;Graham et al, 2009;McDonald, 2007). Operators that use ozonation as a component of their irrigation water treatment system tend to use it in batch format.…”

“…Tropospheric ozone enrichment (photochemical smog) elicits phytotoxic reactions in a wide array of plant species over a range of concentrations (Bell and Treshow, 2002). Although phytotoxic, recent studies suggest that under conditions of controlled application in aqueous solution, ozone can be safely applied (foliar and directly to substrate) to select horticultural crop species (Fujiwara and Fujii, 2002;Graham et al, 2009Graham et al, , 2011Ohashi-Kaneko et al, 2009;Sloan and Engelke, 2005). There is also limited evidence that ozone application to the root zone can improve some plant performance metrics (Graham et al, 2011;Sloan and Engelke, 2005).…”

“…The objectives of the presented studies were to: 1) examine contact time (concentration multiplied by the time of exposure) as a process control parameter for liverwort management; 2) establish initial aqueous ozone toxicity thresholds for liverwort; and 3) evaluate the response of liverwort to aqueous ozone at exposure levels and application frequencies that are consistent with the tolerance thresholds of select woody perennial nursery species established previously (Graham et al, 2009).…”