The Use of Hydrogen Peroxide and Silver Nanoparticles in Horticulture

Using this compound in gaseous form is more effective than in liquid form, as it disinfects faster at low and high temperatures and, therefore, can be applied in lower concentrations than when administered in liquid form (McDonnell 2014). According to the cited author, using H₂O₂ does not risk harmful microorganisms becoming resistant to it because its action is nonspecific, unlike that of antibiotics. According to Nikkhah et al. (2010), hydrogen peroxide is one of the most commonly used disinfectants for fruit packaging. Linley et al. (2012) indicate the possibility of using the agent for disinfecting tools and water, including drinking water, and in the processing of agricultural products, for disinfecting rooms, greenhouses, plastic tunnels, and storage rooms. As one of the significant advantages of the agent, the authors indicate the safety of its use, the lack of unpleasant odor, and the possibility of using the disinfected rooms soon after treatment. In a concentration from 3 to 6% and the fogging time from 10 minutes to 10 hours, depending on the intensity of contamination and the variety of microorganisms, H₂O₂ can be used to disinfect garden substrates, seedlings, and the root system of fruit and ornamental shrubs and trees.

When decontaminating soil and reusing growth substrates, H₂O₂ decomposes pesticide and herbicide residues by oxidizing them (Newman 2004). Its effectiveness is limited in a high organic substrate. ZeroTol is recommended as a pesticide for use in organic crops and as a sterilizer for the disinfection of greenhouses and gardening equipment to protect plants against bacteria, fungi, and viruses (Miyasaki et al. 1986). Rapid wound healing has been observed using H₂O₂ as a fogging agent on plant material with new lesions. Vänninen and Koskula (1998) showed that H₂O₂ could be used as a spray on seedlings and older cucumber plants grown under mineral wool covers as an algicide against green algae, on which water moths (Scatella stagnalis) feed. Reciclean containing H₂O₂ reduced algae growth by 40–60%, thus reducing the number of water moths by 73–92%. The agent also minimized algae growth in the water and on the surface of other substrates, primarily when used in the initial stage of algal development.

According to Japhet et al. (2022), the constant addition of H₂O₂ to water in a closed circuit allows it to water plants, inhibiting clogging and biofilm formation in the irrigation system. Barta and Henderson (2000) proposed the use of H₂O₂ as an alternative to conventional bleach for disinfecting hydroponic plant growth systems. At a concentration of 0.5% it reduces the microbial population to almost zero, but this must be repeated during cultivation. Bosmans et al. (2016) showed that H₂O₂ can effectively reduce biofilm formation by rhizogenic bacteria, but its concentration should be adapted to the particular Agrobacterium rhizogenes strain. Parke and Fisher (2012), researching the possibilities to propagate plants with disinfecting water, indicate that, apart from chlorine and copper compounds, hydrogen peroxide is particularly effective when the Pythium and Phytophthora genera are present in the production environment. Stewart-Wade (2011) suggests the elimination of organic residues from the water used in plant production on which microorganisms live, which makes it possible to almost wholly avoid the development of potential pathogens. Fredrickson (2005) indicated that adding hydrogen peroxide to water used for watering plants removed chlorine and sulfur residues, components of pesticides, and fertilizers from the soil, and the released oxygen caused faster decomposition of dying roots, eliminating potential plant pathogens and algae growth. Consequently, such action of the agent affected the increase in yield and plant quality. The agent is also recommended for treating seeds, soaking or watering seedlings, bulbs, and tubers, and spraying crops in the field and under covers. In a study by El-Mougy et al. (2008), hydrogen peroxide was a helpful agent for postharvest protection of strawberry fruits against Botrytis cinerea and disinfection of water, surfaces, and tools.

The first pesticides containing hydrogen peroxide were registered in 1977 (Anonymous 2015). According to the United States Environmental Protection Agency (EPA 2014) and the Canadian General Standards Board (CGSB 2011), by 2014, there were 167 hydrogen peroxide-based agents registered in the US. Currently, many scientific reports prove the effectiveness of H₂O₂ as a biocide.

The protection of plants against diseases and pests as a result of H₂O₂ application is associated not only with the direct attack and destruction of microorganisms by this compound but also with its impact on plant metabolism, which causes the plant to acquire defensive capabilities as a result of hypersensitivity responses and systemic acquired resistance (SAR). Applying H₂O₂ mimics the process generated by plants in response to pathogen attack by rapidly producing reactive oxygen, known as the “oxygen burst” (Lei et al. 2014). The cited authors observed that Arabidopsis cells attacked by aphids accumulated H₂O₂, leading to a hypersensitivity reaction and the cells’ death. Numerous papers, including Bestwick et al. (1997), showed the appearance of H₂O₂ at the sites of penetration by bacterial pathogens. Small H₂O₂ molecules, after penetrating cell membranes, quickly decompose into reactive oxygen and water upon contact with biological material and show a biocidal effect on a broad spectrum of bacteria, fungi, and viruses. Baatout et al. (2006) report that H₂O₂ increases the permeability of cell membranes, increasing with the concentration of the compound, and Qin et al. (2011) emphasize its negative impact on the mitochondria of fungal proteins.

In the scientific literature, it is possible to find both reports on experiments with H₂O₂ and recommendations for using it to fight pathogenic microorganisms and parasites. For example, hydrogen peroxide was found effective against several fungal pathogens, such as downy mildew (Pseudoperonospora cubensis) on cucurbits (Kuepper 2003), potato late blight (Phytophthora infestans) (Kuepper & Sullivan 2004), and apple scab (Venturia inaequalis) (Phillips 2005). Hydrogen peroxide has been recommended in organic tomato production (Diver et al. 1995). In addition, H₂O₂ was effective in controlling tomato wilt (Ralstonia solanacearum) (Hong et al. 2013), potato blackleg (Dickeya solani), pepper golden mosaic (PepGMV) (Mejía-Teniente et al. 2019), European stone fruit yellows (Musetti et al. 2005), the nematodes Meloidogyne javaica (Karajeh 2008); Jansen et al. 2002; Bolm et al. 2004), Bactrocera spp. flies on Syzygium samarangense (Khandaker et al. 2018). Hafez et al. (2020) reported that in an open-field experiment, H₂O₂ limited the infection of pear trees with Erwinia amylovora. Thakulla et al. (2022) studied the addition of hydrogen peroxide in the form of ZeroTol preparations (H₂O₂ + peracetic acid) and PERpose Plus (H₂O₂ + hydrogen dioxide) in hydroponic tomato cultivation. They found adverse effects of both preparations on the growth, dry and fresh weight of algae but a positive impact on tomato plants. The US organic farming guidelines allow the use of hydrogen peroxide-based disinfectants, fungicides, and algicides (EPA 2009).

Despite many reports on the positive effect of H₂O₂ on reducing plant diseases, there are doubts about whether this compound can be recommended for large-scale production. Miller (2006) did not recommend H₂O₂ as a biopesticide due to its short-term activity and assumed that this compound could be effectively used only for surface disinfection and water decontamination. However, its use against plant pathogens is risky, especially in field production.

H₂O₂ participates in plant metabolism in many ways, including activating plant genes related to resistance (Orozco-Cárdenas et al. 2001). An increased concentration of this compound was found in places of infection and damage, where it acts as a direct biocide and a factor accelerating wound healing (Orozco-Cárdenas et al. 2001). This process was observed within 4 hours of leaf tissue damage (Olson & Verner 1993). In addition, more active oxygen in the tissues stimulates metabolism and, depending on the conditions, acts as a transmitter of signals initiating various biochemical reactions. In this role, H₂O₂ activates the processes leading to damage regeneration, stimulating growth, and making plant organisms resistant to biotic and abiotic stresses. These activities are initiated by releasing oxygen, similar to an oxygen burst, which manifests the initiation of plant defense reactions in response to biotic and abiotic stress factors. For example, an increased oxygen concentration was observed in tomatoes at the inoculation site with the fungus Cladosporium fulvum (Borden & Higgins 2002). Chen et al. (1993) believe that salicylic acid, as an inducer of plant resistance to adverse environmental factors, limits the activity of catalase, which leads to the accumulation of hydrogen peroxide, thereby enhancing its effect. The consequence is the thickening of cell walls and the activation of genes that can induce systemic resistance of plants to pathogens. For example, H₂O₂ induced the resistance of damaged fruits to infection by Penicillium spp. (Janisiewicz et al. 2016). Increased amounts of H₂O₂ accumulated in places of mechanical damage to apples and citrus fruits resulted in injury healing (Macarisin et al. 2011). One of the factors inducing resistance is the stimulation of lignin synthesis, which is deposited in the cell walls of infected plants, preventing further pathogen spread (Ros Barceló 1998; Hückelhoven et al. 1999; Płażek 2011). A similar response was found by Martinez et al. (2000) in the case of cotton infection by Xanthomonas campestris pv. malvacearum. H₂O₂ stimulates wound healing (Ros Barceló 1998). External application of H₂O₂ in amounts not causing oxidative stress eliminated the toxic effects of stress caused by copper, nickel, salinity, drought, and low and high temperatures, among others. Uchida et al. (2006) demonstrated the biosynthesis of osmoprotectants in plants treated with H₂O₂ in response to abiotic stresses. Szpunar-Krok et al. (2020) reported a positive effect on the efficiency of the potato photosynthetic apparatus using H₂O₂ at a concentration of 1%. Adding H₂O₂ to the soil increased photosynthetic activity and, in the end, the amount of soluble sugars in melon fruit (Ozaki et al. 2009).

Torres et al. (2003), researching the resistance of apples to Penicillium expansum, which causes fruit rot during storage, found an increase in the concentration of hydrogen peroxide and reactive oxygen species (ROS) in the harvested fruits as a result of artificial inoculation with the pathogen, followed by an increase in the resistance to it. Bestwick et al. (1997) found a hypersensitive response in lettuce to Pseudomonas syringae pv. phaseolicola as early as 5–6 hours after cell inoculation with the bacterium. Olson and Verner (1993) and Wu et al. (1997) showed that the agent could make potato plants resistant to several species of pathogens, causing an even several-fold increase in the concentration of salicylic acid in the affected tissues and an increase in the amount of lignin in the shoots and roots. Research by Türküsay and Tosun (2005) showed that using hydrogen peroxide for spraying tomato plants infected with Clavibacter michiganensis ssp. michiganensis can induce resistance to this bacterium. In a study conducted on cucumbers, Lee et al. (2004) showed that when there was a sharp drop in temperature, hydrogen peroxide accumulated in the cytoplasmic membranes of root cells, and the water uptake by the root system decreased by half. This action of the agent affects limiting the freezing of plants. According to Mejía-Teniente et al. (2019), exogenous application of H₂O₂ induced pepper plant resistance to PepGMV. Borden and Higgins (2002) showed that reactive oxygen species formed in tomatoes infected with Cladosporium fulvum strongly limited plant colonization by this pathogen. Price and Lee (1970) found that the bacterium Lactobacillus plantarum produced hydrogen peroxide, which strongly inhibited the growth of Pseudomonas spp. and other pathogenic bacteria.

Research by Webber et al. (2007) showed that foliar and soil applications of H₂O₂ accelerate the development of the root system and increase the number of nasturtium flowers. The authors believe this is related to eliminating soil pathogens, although more oxygen can accelerate faster root growth. Experiments conducted by Khandaker et al. (2018) showed a positive effect of H₂O₂ on the growth and development of wax apple (Syzygium samarangense). Spraying trees with hydrogen peroxide in concentrations from 0.05% to 0.2% at weekly intervals increased the number and size of fruit on the trees, reduced fruit drop, and increased fruit yield and quality. The fruits had a higher content of potassium, anthocyanins, and carotene, on average about 60%, but also a higher amount of flavonoids, sugar, proteins, and antioxidants. In the experiments by López-Delgado et al. (2005), spraying potatoes with hydrogen peroxide from the 3rd to the 10th week of their cultivation increased the thickening of shoots. It caused a significant increase in lignin in the conductive bundles and faster growth of plants. Al-Mughrabi (2010) showed that fogging potato tubers during storage and treating them with H₂O₂ before planting resulted in better germination, increased shoot number, and a higher yield of better quality tubers. On the other hand, Orozco-Cardenas and Ryan (1999) emphasize that an agent present in the conductive bundles can inhibit the movement of harmful viruses, bacteria, and fungi. It is also essential to use H₂O₂ to quickly heal potato tubers or other plants damaged during harvest and transport (Orozco-Cárdenas et al. 2001). In the technology developed by Afek et al. (2000) and Al-Mughrabi (2007), the agent was used to extend potato storage for up to 6 months.

Hydrogen peroxide has also found valuable applications in spraying, bathing, or gasification in storing vegetables, fruits, and flowers. It is used to remove bacterial and fungal contamination from the surface of fruits and vegetables and as an addition to the solution in which flowers are stored. In the storage of citrus fruit, it was used as a disinfectant, replacing the previously used formaldehyde (Smilanick et al. 2014). Bathing apples in an aqueous solution of 1% H₂O₂ reduced the Escherichia coli population (Sapers & Sites 2003). However, the same treatment was ineffective for decontaminating melons, meaning that the concentration and duration of exposure must depend on the fruit surface area and the plant growing conditions (Ukuku 2004). On the other hand, bathing whole melon fruit in 2.5% and 5% solutions effectively removed Salmonella spp. from the surface, while in the storage of cut fruit, the fruit had to be bathed whole and then cut. Using H₂O₂ at 1% and 1.5% concentrations on harvested strawberry fruit protected them with a 90% effectiveness against Botrytis cinerea and Rhizopus stolonifer (El-Mougy et al. 2008). However, hydrogen peroxide can have adverse effects, e.g., browning that reduces the quality of fruit, browning of lettuce leaves, and degradation of anthocyanins in berries (Nikkhah et al. 2010; Pietrysiak et al. 2019). H₂O₂ applied in gaseous form minimized the infection of grapes by Botrytis cinerea (Forney et al. 1991). Washing mushrooms in a 5% H₂O₂ solution immediately after harvesting allowed them to be stored at 4 °C without reducing their quality (Sapers et al. 2001). Applying H₂O₂ protected peach flesh against darkening, gradually reducing it (Ding et al. 2009). When stored for four weeks, pepper fruits bathed in a 15% hydrogen peroxide solution maintained high fruit quality, reduced weight loss, and minimized putrefaction (Bayoumi 2008).

In potato storage, it is crucial to maintain their good health by minimizing the development of possible pathogens transferred onto the tubers and preventing the growth of sprouts (Afek et al. 2000; Kleinkopf et al. 2003). Research by Afek et al. (2000, 2001) and Al-Mughrabi (2007, 2010) indicates the possibility of using hydrogen peroxide (HPP with an unknown mixture of stabilizers, and StorOx with 27% H₂O₂) to minimize the development of pathogens causing wet rot of tubers (Erwinia carotovora), alternariosis (Alternaria solani), fusariosis (Fusarium sambucinum), powdery scab (Helminthosporium solani), dry rot (Phytophthora erythroseptica), late blight (P. infestans), and Pythium ultimum. Gachango et al. (2012) confirmed the effectiveness of H₂O₂ in protecting potatoes against F. sambucinum, P. erythroseptica, P. infestans, and P. ultimum in storage. They showed that H₂O₂ completely inhibited the development of P. infestans, with an effectiveness of four times greater for F. sambucinum and six times greater for P. ultimum on tubers, compared to the control. Czajkowski et al. (2013) indicated that among the several agents tested for potato protection against blackleg during storage, only H₂O₂ did not cause toxicity to plants.

Gupta et al. (2018) examined the effect of silver nanoparticles on the growth of rice seedlings. They demonstrated the stimulatory effect expressed as promotion of seedlings length and biomass. Salachna et al. (2019) found that soaking lily bulbs in silver nanoparticle solution stimulated plant growth, accelerated flowering with more flowers, and flowered longer. Prażak et al. (2020) studied the effects of AgNPs on bean seed germination and plant growth parameters at typical and low temperatures. At low concentrations (0.25 mg·l⁻¹), nanosilver stimulated quick and uniform seed germination in the laboratory and positively impacted plant growth and development in the field experiment. A particularly pronounced positive effect was revealed during germination at low temperatures, indicating that nanosilver may activate the tolerance mechanism to environmental stresses. Higher concentrations killed microorganisms but also negatively affected plant growth.

Kim et al. (2012) tested the in vitro sensitivity to AgNPs of several plant pathogens and found that all were sensitive. However, the result depended on the type of fungus and the concentration of the preparation, with the effect increasing with the concentration (up to 100 ppm). Silver administered as AgNO₃ or nanoparticles effectively eliminated or reduced the disease on ryegrass leaves, mainly when it was applied before inoculation with the fungus (Jo et al. 2009). Field experiment results of Lamsal et al. (2011) indicate that silver nanoparticles at a concentration of 10 to 100 ppm were more effective than classical fungicides in controlling pepper anthracnose (Colletotrichum), mainly when used preventively. In a field experiment, Gado et al. (2016) found that AgNPs reduced the severity of a disease on roses caused by Phragmidium spp. by one third. According to Shoaib et al. (2022), using nanosilver to control nematodes such as Meloidogyne incognita, Pratylenchus penetrans, and Tylenchulus semipenetrans is very promising. Al-Azzazy et al. (2019) reported that low dosages of AgNPs reduced the population of phytophagous mites associated with tomato plants in field cultivation.

In addition to the direct impact on microorganisms, silver molecules are involved in inducing the systemic resistance of plants to pathogens (Chen et al. 1993). For example, it was found that silver nanoparticles induced resistance of Arabidopsis seedlings to Pseudomonas syringae pv. tomato (Chu et al. 2012).

Nanosilver has been used to extend the life of cut flowers, and presumably, this is its most indisputable application. Its action is related to the inhibition of the multiplication of microorganisms in the storage solution and in the conductive bundles, through which silver reaches the flower, where it silences the ethylene biosynthesis genes, which are of great importance for the durability of climacteric plants (Basiri et al. 2011; Naing & Kim 2020). The positive impact on the durability of cut flowers has been reported in, for example, carnation (Sedaghathoor 2015), gladiolus (Li et al. 2017), tree peony (Zhao et al. 2018), gardenia foliage (Lin et al. 2019), snapdragon (Rabiza-Świder 2020), peony (Skutnik et al. 2020a), garden cosmos (Skutnik et al. 2020b), Thalictrum aquilegifolium (Poniewozik et al. 2020), lisianthus (Skutnik et al. 2021), tuberose (Paul et al. 2021), Strelitzia (Thakur et al. 2022), alstroemeria (Anvari et al. 2022), and rose (Ha & In 2022). Nanosilver was mainly applied as pulse treatment at 5–20 mg·l⁻¹ for 24 h or as a permanent presence in the liquid in which flower stalks were immersed. Silver has also been recommended as an application on fresh fruits and vegetables to inhibit the reproduction of microorganisms and, as a result, to extend the shelf life (Kale et al. 2021). For example, coating asparagus with a nanosilver solution delayed weight loss, the loss of ascorbic acid and chlorophyll, prevented the growth of microorganisms and, as a result, extended the shelf life by ten days when stored at 2 °C (An et al. 2008). Similar results were obtained for pears and carrots (Fayaz et al. 2009). Motlagh et al. (2013) reported positive effects of storing barberry fruits in plastic bags with the addition of nanosilver.

Silver in ionic form and as nanoparticles were used to improve the effect of in vitro plant cultures (Mahendran et al. 2019; Andújar et al. 2020; Zia et al. 2020). It displays many different functions as an antimicrobial agent and plant growth stimulant. One of the first reports on the effective use of silver (in the form of AgNO₃) concerned the elimination of the bacterial vector (Agrobacterium tumefaciens) from rose callus. Common antibiotics caused callus blackening and impaired shoot organogenesis. Silver nitrate inhibited the proliferation of bacteria and enabled organogenesis (Orlikowska et al. 1996). Nowadays, many authors recommend the use of nanosilver for the decontamination of initial explants, e.g., Arabidopsis seeds (Mahna et al. 2013), nodal segments of rose shoots (Shokri et al. 2015), valerian stems (Abdi et al. 2008), capitulum of gerbera (Fakhrfeshani et al. 2012), Araucaria (Sarmast et al. 2011), lemongrass (Salisu et al. 2014), Pennisetum (Parzymies et al. 2019), and others. Parzymies (2021) reported that nanosilver particles reduced the contamination of explants but also decreased regeneration and slowed down the growth of Aldrovanda vesiculosa. By contrast, Andújar et al. (2020) demonstrated that silver nanoparticles (preparation Argovit^™) reduced contamination and enhanced the growth and multiplication rate of Psidium friedrichsthalianum. Nanosilver or AgNO₃ was added to the medium to protect cultures before contamination and to affect regeneration, multiplication, shoot rooting, and stimulating the production of secondary metabolites (Kim et al. 2017; Mahendran et al. 2019; Mahajan et al. 2022; Tung et al. 2022). Depending on the plant species and goal of in vitro culture, the form and concentration of the agent must be determined experimentally. The most effective in vitro is its inhibitory action against ethylene, especially in ethylene-sensitive plants such as cruciferous vegetables (Chi & Pua 1989; Akasaka-Kennedy et al. 2005) and potatoes (Perl et al. 1988; Ehsanpour & Nejati 2013).

The preparation with these two components is proposed for disinfecting swimming pool water (Martin et al. 2015), surfaces, and equipment where other agents caused corrosion of metal parts, and for disinfecting rooms without the risk of leaving an unpleasant odor in with (Linley et al. 2012). As a result of a 24-month experiment, it was found that the H₂O₂/silver formulation was thermostable and more effective at higher temperatures, which predestines the use of the preparation for disinfecting hot water. Silver is deposited on the inner surfaces of pipes. The positively charged metal binds the negatively charged bacterial walls, destroying the structure of the membranes, which leads to the penetration of H₂O₂ and the death of bacterial cells (Shuval et al. 2009). Darzi et al. (2020) reported removing CGMMV virus particles from the surface of infected seed boxes in a 1% solution of Huwa San TR 50.

Martin et al. (2015) reported that the agent used to disinfect surfaces as well as to disinfect drinking water eliminated Legionella spp., Escherichia coli, Cryptosporidium parvum, Giardia spp., Pseudomonas aeruginosa, Bacillus subtilis, Streptococcus aureus, and others species, without affecting the taste and smell of the water. Wilson (2011) emphasized that Huwa San TR-50 added at the concentration of 200 ppm·m⁻³ disinfected drinking water, eliminating Legionella spp. within 24 hours. The authors speculate that this agent added at a concentration of 15–20 ppm can also kill other species of bacteria.

In Poland, research on the activity of Huwa San TR-50 in the disinfection of water intended for irrigation of horticultural crops was conducted by Orlikowski et al. (2017a, b), showing a reduction in the population of pathogenic fungi from the genera Cylindrocladium, Fusarium, Phytophthora and Pythium. An example can be an 87.5% reduction in Phytophthora cinnamomi by adding 100 ml of the agent per m³ of water.

Huwa San is also a secondary disinfectant, mainly to eliminate carcinogenic trihalomethanes formed after water chlorination. The World Health Organization allows up to 100 μg of silver per liter in drinking water as the active ingredient of Huwa San TR-50 (Martin et al. 2015).

Huwa San TR-50 at a concentration of 10% was used for surface decontamination of initial pistachio shoot explants. It was less effective than HgCl₂ in eliminating surface contaminants and less damaging to the explants (Korkmaz et al. 2022).

Linley et al. (2012) indicate that agents based on silver-stabilized hydrogen peroxide are more and more commonly used as biocides, especially since their environmental toxicity is lower than that of synthetic pesticides. Mahesha et al. (2021), in laboratory tests, studied the effectiveness of preparation based on colloidal silver with H₂O₂ (Alstasan Silvox) against some bacterial and fungal pathogens in vitro and its toxicity to young cotton plants and found that toxicity to plants occurred only at a concentration of 10,000 ppm. Linley et al. (2012) emphasize the much higher activity of the gaseous agent because it reaches the smallest nooks and crannies, surrounding the hyphae and spores of harmful microorganisms.

Introducing agents containing hydrogen peroxide and colloidal silver on the Polish market (Huwa San TR-50, Bisteran) resulted in an interest in its use in protecting horticultural plants, especially ornamental ones, against the most dangerous diseases. In studies by Wojdyła (2012, 2016a, b), the use of the agent at a concentration of 0.05% and 0.1% for repeated spraying plants of cissus, geraniums, willows, and roses protected them with an effectiveness of up to 80% against diseases such as powdery mildew (Oidium sp. and Podosphaera pannosa), rose black spot (Diplocarpon rosae), rust (Puccinia pelargonii-zonalis and Melampsora epitea), and its effectiveness ranged from 60 to 90%. In turn, Włodarek et al. (2016) showed a 60% effectiveness of the agent in protecting brassica vegetables against black cruciferous (Alternaria spp.). Research by Orlikowski (unpublished) assessed the effects of the agent on minimizing the occurrence of soil pathogens of the genera Fusarium, Pythium, and Phytophthora in the substrate. Abundant spraying of the infected substrate with the agent at a concentration of 1 and 2%, followed by thorough mixing, resulted in the elimination of these pathogens in approximately 90%. The agent used for once-repeated spraying of poinsettias with the first symptoms of grey mold (Botrytis cinerea) reduced the development of the disease by about 90%, while prophylactic spraying of rooted chrysanthemum seedlings with this agent protected them entirely against the occurrence of grey mold. Huwa San TR-50 has also proven to combat grey mold on chrysanthemum micro-seedlings acclimatized in a greenhouse (Orlikowska, unpublished data). The use of the agent in the protection of orchard plants has also been tested. Applied at weekly intervals at a concentration of 0.1% for twice-repeated spraying of plum trees with cankers developing on the trunks resulted in wound healing in about 80% within two months (Orlikowski, unpublished data). Spraying ripening raspberries with the first symptoms of the grey mold with a 0.1% agent almost wholly stopped the further development of the disease (Orlikowski, unpublished data). Włodarek et al. (2015) showed that Huwa San TR-50 used to protect Brassica pekinensis against Erwinia and Pseudomonas resulted in better head quality and enabled extended storage.

Soika (unpublished data) showed that spraying roses four times with Huwa San TR 50 in concentrations of 0.05% and 0.1% resulted in a 95% reduction in the rose aphid population on the shoots. The above scientist sprayed thuja plants with a 0.05% Huwa San TR-50 and observed a 60% reduction in the number of thuja beetles. Alhewairini (2017) showed that spraying cotton with an agent at a concentration of 0.1% resulted in the elimination of aphids (Aphis gossypii) in at least 90%. At this concentration, however, the agent did not reduce the honey bee population (Apis mellifera lamarckii). Observations carried out in nurseries of fruit and ornamental trees sprayed with 0.1% Huwa San TR-50 for quick healing of wounds showed that the use of the agent resulted in a drastic reduction in the occurrence of the spider mite (Orlikowski, unpublished data).

Most reports on the effectiveness of Huwa San relate to the control of spider mites on various plants: date palm (Alhewairini & Al-Azzazy 2017), Citrus sinensis (Al-Azzazy & Alhewairini 2019; Alhewairini 2018), Solanum lycopersicum (Alhewairini & Al-Azzazy 2018), olive tree (Al-Azzazy & Alhewairini 2018; Alhewairini et al. 2020), Vitis vinifera (Al-Azzazy & Alhewairini 2020). As Wojdyła (2012) showed, Huwa San TR-50 limits the development of foliar pathogens Podosphaera pannosa, Puccinia pelargonii-zonalis, Diplocarpon rosae and Oidium, and Podosphaera pannosa on rose (Wojdyła 2016a) and Melampsora epitea on willow (Wojdyła 2016b). Huwa San TR-50 reduced tomato diseases caused by Fusarium solani and Rhizoctonia solani (Hamed et al. 2022). This preparation can control Alternaria spp. on Chinese cabbage (Włodarek et al. 2016). Grzegorzewska and Kowalska (2013) write about its use in effectively controlling Sclerotinia sclerotiorum on carrots. Huwa San 25 inhibited the bacterial disease caused by Erwinia amylovora (Hafez et al. 2020) on pear trees while stimulating shoot growth.

The bacterium Agrobacterium rhizogenes causes mad root disease, mainly on cucumbers and tomatoes grown in mineral wool (Martin et al. 2015; Bosmans et al. 2016). Depending on the bacterial frequency, losses can reach up to 30%. For the protection of plants against disease-causing bacteria, it is advised to remove diseased plants immediately after noticing the disease and disinfect communication routes, vehicle tires, footwear, and hands with Huwa San TR-50. Vanlommel et al. (2020) reported that immersing mineral wool bricks once in a bath with Huwa San TR-50 before planting tomato plants reduced the occurrence of the bacterium throughout the entire cultivation cycle. However, in greenhouse tomato cultivation in Belgium, it is recommended to use Huwa San TR-50 throughout the cultivation period, primarily to disinfect the irrigation system (Anonymous 2016).

Huwa San TR-50 stimulated tomato seed germination and seedling growth (Türküsay & Tosun 2005). Stępowska’s research (unpublished) on the use of the agent in the cultivation of peppers showed that Huwa San TR-50 at a concentration of 0.05%, sprayed five times on plants grown in a polytunnel, increased the chlorophyll content in the leaves. As a result, a significant increase in fruit yield and quality were obtained. Not without significance was the beneficial effect of the agent on the soil and the substrate.

Tests of the agent for registration purposes at the National Institute of Horticultural Research in Skierniewice (2012) showed its high effectiveness in the healing of wounds. Within three months of spraying with Huwa San, the scars on damaged trees healed to about 90%. These data indicate the necessity of using Huwa San TR-50 after pruning fruit trees and shrubs to heal injuries caused by storms, post-frost cracks, and injuries caused by physiological disorders. Its use is also helpful for alleviating damage to root vegetables, brassicas, and onions suffered during harvesting and transport. The agent also has a healing effect on plant organs damaged by pests, e.g., insect caterpillars, aphids, cup mites, and spider mites (Soika, unpublished). In the case of the spider mite inhabiting chrysanthemum leaves, the pest was found dead as early as 6 minutes after spraying the plants with Huwa San TR-50 at a concentration of 0.1% (unpublished data). Wojdyła et al. (2022) showed that immersion of hyacinth tubers before planting stimulated their growth and development.

Aharoni et al. (1994) showed that Sanosil-25 containing 48% H₂O₂ and 0.05% silver ions, added to melon fruit baths before storage, reduced the decay caused by Fusarium solani and Alternaria alternata when incorporated into wax-covering fruits. The same preparation applied as short dipping reduced the decay of eggplant and sweet red pepper fruits caused by Botrytis cinerea and A. alternata (Fallik et al. 1994). Huwa San TR-50 was effective against Sclerotinia sclerotiorum on freshly cut carrot slices (Grzegorzewska & Kowalska 2013). Observations on the harmfulness of nine compounds used to protect potatoes against Dickeya solani showed that only Huwa San TR-50 was not phytotoxic to the tubers and strongly limited the development of black leg when tubers were soaked for 15 minutes in the solution (Czajkowski et al. 2013). Therefore, Huwa San can be commonly used to minimize the occurrence and development of pathogens during potato storage (Al-Mughrabi 2010). The presence of organic residues and minerals introduced into the water with fertilizers favors the development of microorganisms that form the biofilm inside the ducts, whose thickness increases gradually during cultivation. Research by Armon et al. (2000) showed that Huwa San TR-50 at a concentration of 0.003% added to water throughout the plant cultivation period strongly reduced biofilm formation.