Author: Eyal Klein Ph.D.

Keep clean & Stay calm – Hishtil professional notes for the grower


Cleanliness is one of the most important factors in the production of healthy plants. With the outbreak of the new COVID-19 pandemic, we looked at the recommendations of the leading professional institutes and gathered information on processes and effective disinfectants; some are also used in agriculture. The Centers for Disease Control and Prevention (CDC) and the US Environmental Protection Agency (EPA) were the major sources for this review and are frequently updated, so it is recommended to check the information regularly. Most of the chemicals that could be used for disinfection are based on chlorine, ethanol, Hydrogen peroxide, quaternary-ammonium, bases or acids. Some of the products contain essential oils and the properties and advantages of each of the groups are discussed. In order to ensure their efficacy, disinfectants should be applied to surfaces and means that are free of visible contamination. Absorb clean cloth in diluted disinfectant and wipe the surfaces, or spray at low volume and small drops that will dry a few minutes later. Fogger, or ULV air-assisted sprayer, are recommended. Nurseries and growers should use new sprayer or totally cleaned from pesticide-residues. Cleaners and disinfectants should be carefully chosen according to their registration, efficacy, active ingredients MRLs and their phytotoxic and health-injury potential.

General principles of cleaning and disinfection

Sanitation is one of the key factors for the production of healthy and high quality propagating materials and plants. However, it is necessary to understand the methodology in order to establish a sanitation protocol that will be economic, effective, and without the risk of phytotoxicity or forbidden residues.

In Hishtil nurseries we make great efforts and collaborate with leading research institutes, suppliers and companies to develop and maintain our disinfection protocols. The basis for an effective disinfection process is the cleaning and removal of contaminants and especially organic residues.

Residues of crops which were infected with various pests, contaminated means of production and also untreated water can be a source of pests and pathogens. Furthermore, pests survive well on organic matter which also serves as a shield against disinfectants. Chemicals such as oxidizers react with the organic matter and will be less effective against the pests; physical means such as UV light (mainly UVC) has low permeability capacity and will not reach the hidden pests.

Therefore, thorough cleaning could significantly reduce the infection risk and will contribute to the disinfection efficiency. The usual means of cleaning are physical - scrubbing with brushes or water pressure and high water temperature which help mainly in removing sticky and greasy substances. The chemical cleaners include soaps and lipid removers. Some of them are used as surface-active ingredients and surfactants that improve cleaning efficiency and could have also disinfection properties, as will be discussed below.

There are several levels of cleanliness from microbial contamination and viruses. The highest level is sterilization - a complete eradication of all organisms. One lower level is high level disinfection (HLD) in which endospore-forming bacteria could survive; the endospore is a dormant and highly resistant cell to preserve the cell's genetic material in times of extreme stress. Disinfection is elimination of some microbial communities while others are weakened or remain non-affected. Sanitation is reduction in the total count of the microorganisms, not necessarily the elimination of a certain group.

The efficacy of physical and chemical means in cleaning, and, in particular, in disinfecting, derives from the target sensitivity, means properties – active ingredient concentration (or output/power), time of exposure (duration) and the environmental conditions that contribute to its activity such as temperature and atmospheric pressure.

For example, sterilization could be achieved by dry air at 250°C for several hours. Exposure time could be shorter if hot steam (water vapor temperature of 120°C) is used, since the heat transfer coefficient of water is higher than that of air. Air circulation or high pressure in the container (over 1.2 Atm.), will allow shorter and more efficient process. Conventional steam applicators could be used for cleaning, but their efficiency as sanitizers depend on steam temperature, steam output (gram per minute) and the duration of exposure.

When choosing a detergent or disinfectant, its regulation should be considered - whether it is registered and designated for cleaning or disinfection and all its ingredients are allowed to be used. For example, quaternary ammonium is a highly effective surface-active chemical and also used as a disinfectant, but its residues are not allowed in organic crops and therefore may contaminate organic production lines.

Another consideration is the potential of toxicity or corrosiveness of the chemical. Some chemicals may cause allergic or irritating response, damage the sanitized surface or the environment, therefore require special protection means. Others have recommended means of application to achieve the maximum efficiency. In any case, the user should consult with the local supplier before application.

It is recommended to use designated application means and to verify that they are totally free form residues of other chemicals or pesticides. Where possible, and depending on the need, it is recommended to use the assistance or services of a company that specializes in disinfection or licensed contractors that specialized in institutional disinfection.

Disinfectants for nurseries work rooms and means against coronavirus COVID 19

Recently, with the global outbreak of the COVID-19 we conducted a literature and technology survey to identify potential products that can be used for both crop protection and disinfection treatments in the nursery, as well as tackling with new threats such as human viruses in the nursery.

COVID-19, a new human virus, SARS-CoV-2 (coronavirus) that causes severe respiratory infections is a global health risk and challenge. The virus is characterized by 2-10 days of incubation and is transmitted between people through contaminated drops, hands or surfaces (1). Kampf et al. reviewed all the available information about the persistence of human and veterinary coronaviruses on inanimate surfaces as well as inactivation strategies with biocidal agents used for chemical disinfection, e.g. in healthcare facilities. The analysis of 22 studies reveals that human coronaviruses such as Severe Acute Respiratory Syndrome (SARS) coronavirus, Middle East Respiratory Syndrome (MERS) coronavirus or endemic human coronaviruses (HCoV) can persist on inanimate surfaces like metal, glass or plastic for up to 9 days, but can be efficiently inactivated by surface disinfection procedures with 62-71% ethanol, 0.5% hydrogen peroxide or 0.1% sodium hypochlorite within 1 minute.

Based on that article, as well as other publications by the Israeli Ministry of Health, international agencies such as WHO, EPA (2), The American Chemistry Council's (ACC) Center for Biocide Chemistries (CBC) (3), and the Center for Disease Prevention (4) and consulting with other virologists and professionals, we reviewed the materials available in Israel and the recommended application method. We focused on disinfectants produced by companies that specialize in cleaning and disinfecting and are capable of supporting the professional and regulatory aspects.

  1. NaDCC disinfectants

This group of chemicals, also known as troclosene sodium, sodium dichloroisocyanurate (SDIC), sodium troclosene; troclosenum natricum is intensively used in hospitals and agriculture. The commercial product that is listed in EPA List N: Disinfectants for Use Against SARS-CoV-2 (2) is Klor-Kleen, but there are many others with the same active ingredients. In Israel there are registered NaDCC products for medical and agricultural use, for example the products of Concept-RX, Klor-Bac and Klor De B. It contains stabilized chlorine which decomposes into active chlorine in the presence of organic or microbial material and at a temperature above 30°C. Concentration of 500 ppm is used for disinfecting surfaces, cooling facilities and food industry. For the COVID-19 1000 ppm is required. This concentration should not be corrosive for stainless steel, plastic, vinyl or rubber surfaces, but it is recommended to wipe or wash with clean water a few minutes after disinfection. Alternatively - spray at low volume and small drops for best coverage and fast drying.

  1. Stabilized hydrogen peroxide

This group is used for general disinfection. Odorless, non-corrosive and non-allergenic, completely decomposes and leaves no residue. No need to wipe or rinse with clean water after application. Could be applied on chlorine-sensitive surfaces and means. There are articles indicating positive bio-stimulation activity in plants. A variety of producers are available for example, Oxonia (Ecolab) and Clorox which are listed in the EPA List N (2) and Huwa-san (5) which as of today is not in the EPA List N (2). In Israel, Zohar-Dalia products have labels for medical, food and agriculture use. For example Perseptal - Hydrogen peroxide stabilized with peracetic acid. It is volatile, almost non-residual, and contains the same active ingredients as OxyCide (Ecolab) (6) which have been included in the EPA List N (2).. Another disinfectant in this group is Virex, containing hydrogen peroxide stabilized in soluble powder. It is new and still under registration in Israel.

  1. Alcohol based products

There are several formulations, liquids and gel. The alcohol concentration (usually ethanol) should be 70% against COVID-19, and it is non-corrosive with low toxicity. However, it is a flammable with invisible flame and therefore should be kept away from heat sources and fire. Additional active ingredients such as chlorhexidine could have a residual effect and also extend its efficacy range against additional pathogens. The gel formulation for hand disinfection might be allergenic, mainly if contain NaDCC, benzoic acid or different essential oils. Water and soap are preferable to clean hand and skin; antiseptic soaps or alcohol with chlorhexidine should be used for clean hand disinfection. Many of the products in EPA List N (2) contain also quaternary-ammonium.

  1. Quaternary-ammonium based products

There are many commercial products in this group, more than 200 of them are listed in the EPA List N (2). One of the well-known products is Lysol®. Since the quaternary-ammonium compounds are effective surface-active ingredients, improve the cleaning process and also disinfect some microbial groups. However they are highly residuals and not allowed in the organic production. In Israel there are the Septoquat, containing quaternary ammonium bromide with isopropyl alcohol, and more effective, the Glutasept, which contain quaternary ammonium chloride, glutaraldehyde and pine oil. Another commercial product with agricultural label is Sporekill, but as of today it is not in the EPA List N (2).

  1. Botanical and essential oil based products

The biocidal activity of different botanical ingredients, including essential oils from herbs is well documented. More specifically, some enveloped viruses and respiratory viruses have been found to be susceptible to botanical terpenes such as thymol, carvacrol, para-cymene and menthol, which are substances found in distilled oils from thyme, savory and mint varieties. For example, the inhibitory concentration of thymol for the HSV-1 envelope virus was as low as 0.002%. Recently some commercial products based on thymol have been included in the CDC COVID-19 website and EPA List N (2).  Bioesque, botanical disinfectant solution can be used against SARS-CoV-2 when used in accordance with the directions for use against Norovirus (Feline Calicivirus surrogate) on hard, non-porous surfaces. Although it is not yet included in the CDC COVID-19 website and EPA List N (2), according to the supplier, It is an EPA registered Bleach-Free, Phosphate Free, non-corrosive disinfectant targeting broad spectrum efficacy; the ready to use formula contains no harsh chemicals and does not require any personal protection equipment, safe for everyday use. No rinse required even on food contact surfaces and NSF certified. Belfor Property Restoration is the largest disaster recovery and property restoration company in the U.S. According to the publication, it uses similar disinfectant, combined with peroxide and peracetic acid solution that kills especially difficult to kill viruses and pathogens yet leaves no harmful residue. These disinfectants can be applied in virtually every type of environment using small, portable electrostatic sprayers. By positively charging a water-based product, electrostatic technology ensures greater surface coverage and adhesion - thus providing more environmentally friendly and effective protection. Citric acid is also active ingredient in some of the products on the EPA List N (2), for example Lysol Bathroom Cleaner.

  1. Virucidal disinfectants used in agriculture

Many of the plant viruses are highly resistant, form stable particles that can persist for long periods on plant debris, in soil and on seed surface. A variety of virucidal chemicals listed for agricultural use, some of them may also be effective against human viruses. Virkon S is well known virucidal agent in agrigulture, containing potassium peroxymonosulfate.  Rely+On™ Virkon™ (7) has been developed specifically for use in the human health market sector and has been added to the EPA List N (2). Menno florades which contain 9% benzoic acid found to be highly effective against tobamo-viruses and was recently registered against the tomato brown rugose fruit virus (ToBRFV) in Germany. Yet, as of today benzoic acid is not listed in the EPA List N (2) thus its efficacy against human pathogens is unclear at this time. There are other chemicals that have been found effective against plant viruses but are not registered for use against human viruses and are currently under trials such as chlorinated trisodium phosphate (Chlorinated TSP) and the ecological cleaner Green Up-D.

  1. Nano-chemicals

There are several innovative developments which use bactericide halogens (Chlorine, Iodine, Bromine) or metals (Copper, Silver) in fibers that can be combined with different materials and fabrics and give them antiseptic properties. For example, Cupron is a copper-based antimicrobial technology company that harnesses the properties of copper for healthcare, consumer, industrial, & military applications. They developed a surgical mask containing the copper fibers that inactivate the viruses that are attached to the mask. Some of these technologies are being tested at Hishtil as part of projects to develop similar technologies for use in agriculture.

Literature and sources

  1. Kampf, G., Todt, D., Pfaender,  , Steinmann, E., 2020. Persistence of coronaviruses on inanimate surfaces and their inactivation with biocidal agents. Journal of Hospital Infection 104: 246-251.