Home remedies for pest and disease problems experienced by plant consumers abound on blogs, forums, and social media groups. However, neither the threshold for phytotoxicity nor efficacy of most of these treatments has been subjected to evaluation under replicated or controlled conditions.
H2O2 is a well-known oxidizing agent often used as a remedy by consumers to treat algae and root decay from presumed root disease on interior plants, as well as to encourage root growth and health. Specifically, H2O2 is used by many consumers and orchid (Orchidaceae) enthusiasts as a treatment for root decay, presumed to be caused by root rot pathogens, in orchids (e.g., Bottom, 2017; Miss Orchid Girl, 2014). In agricultural production systems, H2O2 is used successfully as a treatment to control plant pathogens in irrigation water (Raudales et al., 2014). Baldry (1983) discussed the antimicrobial properties of H2O2, which act effectively as both a bactericide and a sporicide. Ali (2018) reported that seed treatment and soil drenching with 0.25% to 2% H2O2 in greenhouse conditions suppressed root rot pathogens Fusarium solani, Pythium, Rhizoctonia, and other disease organisms, and improved plant survival of thyme (Thymus vulgaris). Webber et al. (2009) concluded that anecdotal reports of H2O2 in irrigation solutions resulting in growth stimulus may be a result of decreasing or eliminating diseases in substrate rather than serving as a direct stimulus to the plant.
However, like most home remedies, using H2O2 on orchid roots has not been investigated in a controlled study to determine safety or efficacy of use. As a reactive oxygen species (ROS), H2O2 can harm cell nuclei, proteins, and lipids of living cells when dosed too high (Krumova and Cosa, 2016). Phytotoxicity from H2O2 has rarely been quantified and characterized on horticultural crops. Webber et al. (2009) reported that soil application of 0.05% to 0.1% H2O2 decreased nasturtium (Tropaeolum majus) foliage dry weight and flower number. Eicher-Sodo et al. (2019) characterized its phytotoxic effects on common microgreens and lettuce (Lactuca sativa) cultivars. Although applied to foliage rather than roots, they found that the same concentration of H2O2 caused unique responses in each cultivar tested, suggesting a broad range of phytotoxicity effects even within the same type of plant (Eicher-Sodo et al., 2019).
Because phalaenopsis orchids (Phalaenopsis hybrids) are epiphytic, their roots have a unique absorptive complex of velamen and exodermis that, compared with the roots of other plant species, takes in moisture and mineral nutrients passively, and protects from dehydration and physical damage (Bercu et al., 2011). As such, their epiphytic roots are managed differently than those of other interior plant species. Notably, consumers can easily overwater epiphytic orchids, which leads to root decay (Bottom, 2012).
The objective of this trial was to determine the rate at which H2O2 causes symptoms of phytotoxicity in phalaenopsis orchids, and the highest rate that can be used safely by consumers. The focus of this study was on the development of phytotoxicity and not on treatment efficacy. However, we also evaluated the secondary effects related to plant longevity and algae reduction in the root zone after H2O2 treatment.
Ali, A.A.M 2018 Role of hydrogen peroxide in management of root rot and wilt disease of thyme plant J. Phytopathol. Pest Mgt. 5 1 13 https://doi.org/10.1111/j.1365-2672.1983.tb02637.x
Baldry, M.G.C 1983 The bactericidal, fungicidal and sporicidal properties of hydrogen peroxide and peracetic acid J. Appl. Bacteriol. 54 417 423 https://doi.org/10.1111/j.1365-2672.1983.tb02637.x
Benzing, D.H., Ott, D.W. & Friedman, W.E. 1982 Roots of Sobralia macrantha (Orchidaceae): Structure and function of the velamen–exodermis complex Amer. J. Bot. 69 608 614 https://doi.org/10.2307/2443070
Eicher-Sodo, M., Gordon, R. & Zheng, Y. 2019 Characterizing the phytotoxic effects of hydrogen peroxide on common microgreen species and lettuce cultivars HortTechnology 29 283 289 https://doi.org/10.21273/HORTTECH04255-18
Krumova, K. & Cosa, G. 2016 Overview of reactive oxygen species 1 21 Nonell, S. & Flors, C. Singlet oxygen: Applications in biosciences and nanosciences. Royal Society of Chemistry Cambridge, UK https://doi.org/10.1039/9781782622208-00001
Raudales, R.E., Parke, J.L., Guy, C.L. & Fisher, P.R. 2014 Control of waterborne microbes in irrigation: A review Agr. Water Mgt. 143 9 28 https://doi.org/10.1016/j.agwat.2014.06.007
Webber, C.L. III, Webber, C.L. Jr. & Sandtner, S.J. 2009 Impact of hydrogen peroxide as a soil amendment on nasturtiums J. Env. Monitoring Restoration 6 110 113