Treatment technologies

Copper ionization system

Greenhouse and nursery growers recognize the importance of conserving water and reducing runoff, but recycling irrigation water can increase the risk of transmitting waterborne plant pathogens. Treatment technologies make it easier and safer to conserve water. With many options to choose from, selecting the best technology can be challenging. The Water Education Alliance for Horticulture can help.

This page provides key information on several available technologies with links to additional information. Under the links page, you'll find articles, websites, and videos including information on how to use and combine technologies, and the possible damage to crop plants.

Click on the headings below for key information about some of the most common water treatment technologies.

Chlorine gas

	Tradename(s)	Chlorinators Incorporated, manufacturer of Regal
	Disinfecting action	Chlorine kills bacteria through a fairly simple chemical reaction. The chlorine added to water breaks down into many different chemicals, including hypochlorous acid (HOCl) and hypochlorite ion (OCl-). Both kill microorganisms and bacteria by attacking lipids in cell walls, destroying enzymes and structures inside cell, rendering them oxidized and harmless. Hypochlorous acid oxidizes organisms in several seconds, while hypochlorite ion takes up to 30 min. Reasons for chlorination: to oxidize soluble ferrous iron to insoluble ferric iron, which can be removed by filtration and to control bacteria growth in the system, which helps control iron slime.
	Injection method	Chlorine gas is diffused through the water, via an ejector with venturi nozzle, where it combines with water to form hypochlorous acid (HOCl) and hydrochloric acid (HCl). To ensure safety, manufacturers have developed chlorine gas injectors that work on a vacuum principle. A venturi injector is used to create a vacuum which actuates the injector. This design prevents chlorine gas from being injected unless the irrigation system is operating so that the gas is immediately dissolved in irrigation water.
	Dosage	0.5 to 2 ppm free chlorine 2 ppm controls zoospores of several Pythium and Phytophthora species
	Technical data	Cl2 is the chemical formula for chlorine gas. Chlorine gas is 100% pure and does not degrade. It is virtually impossible to contaminate in the cylinder. It is vacuum safe with no pressure lines.
	Monitoring	Choose a test kit or meter that measures free chlorine- not total chlorine or combined available chlorine Monitor pH to ensure appropriate balance between HOCl and OCl-
	Residual effect	Yes Durability of HOCl in greenhouse depends on organic load in water, temperature, presence of UV light, and concentration of disinfectant
	Sensitivity	The relative concentration of HOCl and OCl- is affected by pH. HOCl (the stronger oxidizer) is favored at pH 6.0 - 7.5; OCl- at pH > 7.5 Below pH 4.0, off gassing can occur
	Interaction with water quality	The primary effect of gas chlorine is to lower pH. This improves disinfection by increasing hypochlorous acid amount. The change in pH depends on how much chlorine gas is injected and on the buffering capacity of the water. In water with high iron levels, chlorine in any form will cause iron to precipitate. Proper filtration after chlorination will remove precipitated iron and will improve water quality and reduce buildup in irrigation system. Chlorine will react with hydrogen sulfide to form elemental sulfur. Because some of the chlorine is used up by reacting with the sulfide or ferrous ions, additional chlorine must be provided for these reactions to occur. Enough residual chlorine must be injected to control sulfur or iron bacteria, or algae, which can clog micro-irrigation systems.
	Challenges	Requires special equipment, ventilation, and handling (as with all chemicals) to ensure worker safety As with all chlorine application methods, higher than recommended concentrations can be toxic to plants.
	Combining technologies	Because chlorine can react with some metals and plastics, always check with the manufacturer of your irrigation system components to make sure that problems will not occur if chlorine is injected. Gas chlorine has an advantage because it is contained in a closed cylinder where no mixing is required, in contrast to chlorine bleach which is held in mixing tanks. Accidental mixing of chlorine and fertilizer in a container is extremely dangerous, as it will create a thermo-reaction that can be explosive. The contact of fertilizer and chlorine after it has been injected into the system is not hazardous.
	Links	display » Sensitivity of Pathogens Inocula to Chlorine Dioxide Gas. Chlorine gas at relatively 25mg/L can be used to disinfect inert surfaces from Penicillium, Botrytis and Alternaria pathogens. Chastagner, G.A. and Riley, K.L. (Washington State University) Acta Horticulturae Gas chlorination Chlorine gas discussion from our series on water treatment for pathogens and algae. Majka, J.M., W.R. Argo, P.R. Fisher, and C. Hong (Water Education Alliance for Horticulture) GMPro, Aug 2008:17-19 Chlorination and post harvest disease control Written from a post-harvest perspective, this article explains the chemical action of different forms of chlorine, and factors that influence the activity of chlorine (e.g. pH). The first page of the article is posted here; to find the complete article, please conduct a web search of the Journal title. Boyette, M.D., D.F. Ritchie, S.J. Carballo, S.M. Blankenship, and D.C. Sanders (North Carolina State University) BoyetteetalHortTech(chlorination).pdf HortTechnology Volume 3 Issue 4: 395-400 Treating irrigation systems with chlorine Chlorine is increasingly being used for cleaning and maintaining irrigation systems. This article provides information on sources of chlorine and the amounts required for treating irrigation water and systems to control pathogen growth. Clark, G.A. and A.G. Smajstrla (University of Florida) Edis Grower 101: Get cultured- how to adjust irrigation water pH Chlorine treatment of nursery irrigation systems is probably one of the most popular methods of pathogen control. This article discusses the advantages, disadvantages, and different types of chlorine treatment. Merhaut, D.J. (University of California, Riverside) GPN Volume 15 Issue 4: 40
	Additional info	Chlorine gas costs about $1.00 per lb, averaged across the U.S., and is the lowest cost form of chlorine per ppm. Depending upon water quality and demand for Cl2, one lb. of Cl2 can treat 24,000 gallons of water. The cost is $1.00 to treat 24,000 gallons. Installation of nursery systems is typically in the range of $3,500 to $7,000.

Sodium hypochlorite

	Tradename(s)	There are many manufacturers of liquid bleach (sodium hypochlorite, NaOCl). Clorox has an EPA-registered formulation for greenhouse use Hanna Instruments manufactures an NaOCl injection and control system
	Disinfecting action	Changes chemical structure of organic material through oxidation-reduction reaction Reacts with water to produce hypochlorous acid (HOCl) and hypochlorite ions (OCl-)Both HOCl and OCl- act as oxidizers, but HOCl acts more quickly HOCl and OCl- exist in equilibrium- HOCl is favored at pH <7.5
	Dosage	0.5 to 2 ppm free chlorine 2 ppm controls zoospores of several Pythium and Phytophthora species
	Technical data	Liquid NaOCl solutions (5% to 15% chlorine) are injected directly into irrigation water Requires injector that is resistant to very corrosive chemicals and has a very high injection ratio
	Monitoring	Choose a test kit or meter that measures free chlorine- not total chlorine or combined available chlorine Monitor pH to ensure appropriate balance between HOCl and OCl- Inline sensors are available for NaOCl systems
	Residual effect	Yes Durability of HOCl in greenhouse depends on organic load in water, temperature, presence of UV light, and concentration of disinfectant To prevent degradation of NaOCl, do not store in metal container
	Sensitivity	The relative concentration of HOCl and OCl- is affected by pH. HOCl (the stronger oxidizer) is favored at pH 6.0 - 7.5; OCl- at pH >7.5 Below pH 4.0, off gassing can occur
	Interaction with water quality	Increases pH, but effect is very slight at recommended concentration, especially when buffered by water alkalinity In water with high iron concentration, can cause precipitate to form. Precipitate can be removed by filtration Reacts with hydrogen sulfide to produce elemental sulfur If your water is high in iron or hydrogen sulfide, additional NaOCl must be added to provide enough residual to control pathogens and any sulfur or iron bacteria that may grow
	Challenges	Do not mix with any other chemicals, particularly fertilizers or acids Requires corrosive resistant injector with high injection rate NaOCl has a limited shelf life - 1 to 2 mths. Warm temperatures and sunlight speed up its degradation
	Combining technologies	Do not mix with any other chemicals, particularly fertilizers or acids
	Links	display » Surface sanitation: efficacy of disinfestants applied to plant production surfaces Comparison of efficacy of several chemicals including bleach, activated peroxygen (ZeroTol), quaternary ammonium chloride (Greenshield), and other products for control of Botrytis cinerea spores on different surfaces, and emphasizes that a high rate is required on porous production surfaces such as wood. W. E. Copes (USDA-ARS) 2003 SNA Research Meeting Proceedings Vole 48:212-214 Treating irrigation systems with chlorine Chlorine is increasingly being used for cleaning and maintaining irrigation systems. This article provides information on sources of chlorine and the amounts required for treating irrigation water and systems to control pathogen growth. Clark, G.A. and A.G. Smajstrla (University of Florida) Edis Chlorination and post harvest disease control Written from a post-harvest perspective, this article explains the chemical action of different forms of chlorine, and factors that influence the activity of chlorine (e.g. pH). The first page of the article is posted here; to find the complete article, please conduct a web search of the Journal title. Boyette, M.D., D.F. Ritchie, S.J. Carballo, S.M. Blankenship, and D.C. Sanders (North Carolina State University) BoyetteetalHortTech(chlorination).pdf HortTechnology Volume 3 Issue 4: 395-400 Effect of pH on the efficacy of sodium hypochlorite solution as cleaning and bactericidal agents Reports how pH affects sodium hypochlorite's use as a bactericide and a cleaning agent. Sodium hypochlorite is better at removing biofilm at higher pH, but once the bacteria is free from the biofilm, it is more effectively killed at lower pH. Fukuzaki, S., H. Urano, and S. Yamada (Industrial Technology Center of Okayama Prefecture) Journal of The Surface Finishing Society of Japan Volume 58 Issue 8: 465-469 Disinfect with sodium hypochlorite Like all other water treatments, sodium hypochlorite poses some safety risks. This article offers guidelines and protocols for the safe handling, storage, and use of sodium hypochlorite. Callery, A.G. (Portacel, Inc.) CEP Magazine Volume 99 Issue 3: 42-46 Characterization and control of Pythium pathogens in recycled irrigation water This article discusses the efficacy of current Phytophthora chlorination controls for Pythium control. Kong, P., P.A. Richardson, and C. Hong (Department of Plant Pathology, Physiology, and Weed Science, Virginia Polytechnic Institute and State University) KongetalApril2004(Pythiumreport).pdf Research Report F-2004-2, Floriculture Industry Research and Scholarship Trust Efficacy of chlorine on multiple species of Phytophthora in recycled nursery irrigation water Reviews advantages and disadvantages of various water treatment technologies for Phytophthora control, develops guidelines for chlorination using sodium hypochlorite. Hong, C.X., P.A. Richardson, P. Kong and E.A. Bush (Virginia Polytechnic Institute and State University) Plant Disease Volume 87 Issue 10: 1183-1189 Hygiene in the nursery: Disinfecting production surfaces; cement, gravel, capillary mats and sand beds Advice and guidelines for sanitizing porous surfaces in the greenhouse. Tested efficacy of copper ionization, chlorination, and quaternary ammonium compounds against fungi, bacteria, and nematodes on several different surfaces. Stovold, G. (Tropical Fruit Research Station, Alstonville, AU) The Nursery Papers Volume 2000 Issue 5: 1-4 Dose curves of disinfestants applied to plant production surfaces to control Botrytis cinerea Sanitation is a proven component of limiting the spread of pathogens. In this study, lethal dose curves are calculated for six disinfectants (including hydrogen dioxide, quaternary ammonium compounds, and sodium hypochlorite) applied to seven different surfaces contaminated with Botrytis. Copes, W.E (USDA Small Fruit Experiment Station) Plant Disease Volume 88 Issue 5: 509-515 Heat treatments control extension growth and enhance microbial disinfection of minimally processed green onions Study shows that heat treatment in combination with chlorination is more effective at post harvest microbial disinfection than either treatment alone. Abstract available, subscription or purchase required to view full article. Cantwell, M.I., G. Hong, and T.V. Suslow (University of California, Davis) HortScience Volume 36 Issue 4: 732-737 Methods to control Pythium and Phytophthora in cold plastic houses In this study, sodium hypochlorite and UV ares used to treat water infested with Pythium and Phytopthora. Sodium hypochlorite reduced plant mortality, but the best plant health was observed when the water was not infested with pathogens in the first place. Berenguer, J.J., I. Escobar, and M. Garcia (Estacion Experimental, La Nacla, Granada) Berengueretal2001ActaHort(Pyth&Phyt_cold_plastic_houses).pdf Acta Horticulturae Volume 559: 759-763 Grower 101: Get cultured- how to adjust irrigation water pH Chlorine treatment of nursery irrigation systems is probably one of the most popular methods of pathogen control. This article discusses the advantages, disadvantages, and different types of chlorine treatment. Merhaut, D.J. (University of California, Riverside) GPN Volume 15 Issue 4: 40 Sodium and calcium hypochlorite technologies Specific examples of chlorination systems using liquid sodium hypochlorite or solid calcium hypochlorite, from our series on water treatment for pathogens and algae. Fisher, P.R., J. Huang, A. Looper, D. Minsk, W.R. Argo, R. Vetanovetz, and Y. Zheng (Water Education Alliance for Horticulture) GMPro, July 2008: 15-22 Pythium and recycled irrigation water This article reports a new technique for identifying Pythium species, and provides guidelines for chlorination to control Pythium in recycled water using sodium hypochlorite. Kong, P, P.A. Richardson and C. Hong (Virginia Polytechnic Institute and State University) GPN Volume 14 Issue 5: 32-35 Monitoring Mortality of Pythium zoospores in chlorinated water Using oxidation reduction potential This research shows data that indicate that adjusting water pH prior to chlorination may result in an more efficient control of Pythium. Lang, J.; Rebits, B.; Newman, S.E. and Tisserat, N. (Department of Bioagricultural Sciences and Pest Management, Colorado State University) Plant Health Progress Monitoring mortality of Pythium zoospores in chlorinated water using oxidation reduction potential This research shows data that indicate that adjusting water pH prior to chlorination may result in an more efficient disease control treatment. Adjusting the water to pH to 6.0 prior to chlorination resulted in higher ORP values; therefore, less chlorine is required for complete disinfestation. Lang, J., Rebits, B., Newman, S.E. and Tisserat, N. (Department of Bioagricultural Sciences and Pest Management, Colorado State University) Plant Health Progress Efficacy of chlorine in controlling five common plant pathogens This research article illustrates how the effectiveness of water treatments, more specific chlorine, depends on the pathogen to control and the dose concentration and time. Cayanan,D.F., Zhang, P., Liu, W., Dixon, M., and Zheng, Y. (Controlled Environment Systems Research Facility, Department of Environmental Biology, University of Guelph) HortScience Sensitivity of five container-grown nursery species to chlorine in overhead irrigation water The effect of different concentrations of free chlorine were evaluated in diverse woody container grown plants. The results indicate that a concentration chlorine of 2.5mg/L or less should not result in adverse effect in the plants. Cayanan, D.F., Zheng, Y., Zhang, P., Graham, T., Dixon, M., Chong, C., Llewellyn, J. (Controlled Environment Systems Research Facility, Department of Environmental Biology, University of Guelph) HortScience Response of container-grown nursery plants to chlorine used to disinfest irrigation water An assessment of the effect of 2.4mg/L of free chlorine in the irrigation water on evergreen and deciduous shrubs applied with overhead irrigation. Cayanan, D.F., Dixon, M., Zheng, Y., and Llewellyn, J. (Controlled Environment Systems Research Facility, Department of Environmental Biology, University of Guelph) HortScience Efficacy of chlorine for decontaminating water infested with resting spores of Plasmodiophora brassicae An early study in which chlorine was proved to control club root of cabbage at 2mg Cl /L when exposed for 5 minutes. Under field conditions reduction of the disease was observed at 200mg Cl/L nonetheless reduction of plant quality and stand was also observed under these conditions. Datnoff, L.E., Kroll, T.K. and Lacy, G.H. (Virginia Polytechnic Institute and State University) Plant Disease Greenhouse sanitation: Efficacy of disinfectants on cutting blades using Tobacco Mosaic Virus on petunia as a model. Different commercial and non-commercial disinfectants were evaluated for the efficacy to prevent TMV spread with contaminated razor blades. 1:10 bleach, 20% non-fat milk, 20%non-fat dry milk plus surfactant and 1% Virkon® for 1 minute were the most effective to control TMV spread. Hayes, A.J. (The Ohio State University) Knowledge bank of The Ohio State University Fluctuations of Phytophthora and Pythium spp. in components of a recycling irrigation system A study about the presence of Phytophthora and Pythium in perennial container nursery in which water is recycled. Both pathogens were recovered through out the year; however, chlorination significantly reduced the diversity and total number. Effects of temperature, concentration, age, and algaecides on Phytophthora capsici zoospore infectivity This study evaluated the efficacy of different commercial products when interacted with different temperatures and Phytophthora capsici concentrations on cucumber infection. Effects of temperature, concentration, age, and algaecides on Phytophthora capsici zoospore infectivity This study evaluated the efficacy of different commercial products when interacted with different temperatures and Phytophthora capsici concentrations on cucumber infection. Sodium and calcium hypochlorite principles Chemistry, pH effects, ORP, and mode of action of sodium and calcium hypochlorite from our series on water treatment for pathogens and algae. Fisher, P.R., W.R. Argo, C. Hong, J. Huang, A. Looper, D. Wiegers, R. Vetanovetz, and Y. Zheng (Water Education Alliance for Horticulture) GMPro, June 2008:21-25

Calcium hypochlorite

	Tradename(s)	Accu-Tab chlorination systems and calcium hypochlorite tablets
	Disinfecting action	Changes chemical structure of organic material through oxidation-reduction reaction Reacts with water to produce hypochlorous acid (HOCl) and hypochlorite ions (OCl-) Both HOCl and OCl- act as oxidizers, but HOCl acts more quickly HOCl and OCl- exist in equilibrium- HOCl is favored at pH <7.5
	Dosage	0.5 to 2 ppm free chlorine 2 ppm controls zoospores of several Pythium and Phytophthora species
	Technical data	Tablets or granules are placed in a container (erosion chlorinator) with water A small amount of irrigation water is bypassed through the chlorinator- amount diverted can be manually adjusted with a gate valve to achieve desired ppm
	Monitoring	Choose a test kit or meter that measures free chlorine- not total chlorine or combined available chlorine Monitor pH to ensure appropriate balance between HOCl and OCl-
	Residual effect	Yes Durability of HOCl in greenhouse depends on organic load in water, temperature, presence of UV light, and concentration of disinfectant
	Sensitivity	The relative concentration of HOCl and OCl- is affected by pH. HOCl (the stronger oxidizer) is favored at pH 6.0 - 7.5; OCl- at pH > 7.5 Below pH 4.0, off gassing can occur Corrosion of calcium hypochlorite tablet is sensitive to temperature. At temperatures 40F, larger unit is required
	Interaction with water quality	Increases pH, but effect is very slight at recommended concentration, especially when buffered by water alkalinity In water with high iron concentration, can cause precipitate to form. Precipitate can be removed by filtration Reacts with hydrogen sulfide to produce elemental sulfur If your water is high in iron or hydrogen sulfide, additional calcium hypochlorite must be added to provide enough residual chlorine to control pathogens and any sulfur or iron bacteria that may grow
	Challenges	Do not mix with any other chemicals, particularly fertilizers or acids
	Combining technologies	Do not mix with any other chemicals, particularly fertilizers or acids
	Links	display » Sodium and calcium hypochlorite technologies Specific examples of chlorination systems using liquid sodium hypochlorite or solid calcium hypochlorite, from our series on water treatment for pathogens and algae. Fisher, P.R., J. Huang, A. Looper, D. Minsk, W.R. Argo, R. Vetanovetz, and Y. Zheng (Water Education Alliance for Horticulture) GMPro, July 2008: 15-22 Sodium and calcium hypochlorite principles Chemistry, pH effects, ORP, and mode of action of sodium and calcium hypochlorite from our series on water treatment for pathogens and algae. Fisher, P.R., W.R. Argo, C. Hong, J. Huang, A. Looper, D. Wiegers, R. Vetanovetz, and Y. Zheng (Water Education Alliance for Horticulture) GMPro, June 2008:21-25 Characterization and control of Pythium pathogens in recycled irrigation water This article discusses the efficacy of current Phytophthora chlorination controls for Pythium control. Kong, P., P.A. Richardson, and C. Hong (Department of Plant Pathology, Physiology, and Weed Science, Virginia Polytechnic Institute and State University) KongetalApril2004(Pythiumreport).pdf Research Report F-2004-2, Floriculture Industry Research and Scholarship Trust Chlorination and post harvest disease control Written from a post-harvest perspective, this article explains the chemical action of different forms of chlorine, and factors that influence the activity of chlorine (e.g. pH). The first page of the article is posted here; to find the complete article, please conduct a web search of the Journal title. Boyette, M.D., D.F. Ritchie, S.J. Carballo, S.M. Blankenship, and D.C. Sanders (North Carolina State University) BoyetteetalHortTech(chlorination).pdf HortTechnology Volume 3 Issue 4: 395-400 Treating irrigation systems with chlorine Chlorine is increasingly being used for cleaning and maintaining irrigation systems. This article provides information on sources of chlorine and the amounts required for treating irrigation water and systems to control pathogen growth. Clark, G.A. and A.G. Smajstrla (University of Florida) Edis Grower 101: Get cultured- how to adjust irrigation water pH Chlorine treatment of nursery irrigation systems is probably one of the most popular methods of pathogen control. This article discusses the advantages, disadvantages, and different types of chlorine treatment. Merhaut, D.J. (University of California, Riverside) GPN Volume 15 Issue 4: 40

Hypochlorous acid

	Tradename(s)	Oxcide by Chem Fresh, Inc.
	Disinfecting action	Electrolyzed hypochlorous acid Oxcide, is non toxic to plants and roots. Oxcide mildly oxidizes the water system to prevent mineral deposits from forming in irrigation lines. It oxidizes the structured crystalline formations of hard scale, and converts it to an amorphous powdery form which is soft and washes away. This removes harborage sites for pathogens and does not allow scaled surfaces where biofilm may form, and suppresses growth of algae and fungus. .
	Injection method	Oxcide is a proprietary electrolyzed 0.05% concentration of hypochlorous acid and is applied by any proportional injection system. Typical injection ratio is 1:10,000 to deliver a 0.05 ppm dose. This rate may be adjusted according to water quality conditions.
	Dosage	Oxcide is not a sanitizer, due to the low applied dose levels, and is used in irrigation lines for the prevention and removal of both organic and mineral deposits that can clog emitters and cause inconsistent water flow. Typically this is applied at a dose rate of 1:10,000 application rate. Stock Oxcide is 500 ppm of hypochlorous acid, and applied at 0.05 ppm.
	Technical data	Customer experience includes improvement in flow consistency, clear emitters, prevention of algae growth and suppressed fungal gnats. Used on a variety of applications including spray, mist, flood and drip. Foliar and non-foliar applications. Use on cooling pads and scale removal. Electrolyzed hypochlorous is made from the electrolysis of sodium chloride, and the unreacted or byproduct salts are removed and rejected. This creates a pH neutral and stable solution of hypochlorous acid that has very low salt and ionic content which behaves very differently from other chlorination solutions.
	Monitoring	Dose delivery and concentration may be monitored by a simple DPD test with sensitivity to detect 0.05 ppm. An ORP sensor may also be used to see a dose response. Additionally there are amperometric in-line sensors that may be used to detect 0.05 ppm.
	Residual effect	Oxcide at its prescribed dose rate is non-toxic and non-hazardous. It creates a mildly oxidizing effect in the water and reduces bilfilms. This action reduces overall stress on the plants, and does not have any cumulative effect in the greenhouse.
	Sensitivity	Oxcide is sensitive to pH changes, and becomes ineffective at pH levels above pH 8.0. High levels of turbidity and EC may require higher dose rates to be effective. High level of organic material, or the presence of Iron, Manganese or Sulfur will also create a higher demand in the water. It is recommended to add Oxcide in to the water system prior to fertilizer injection so it may condition the water before the fertilizer burden.
	Interaction with water quality	Oxcide neutralizes and oxidizes the carbonates in the water, thus reducing alkalinity. The Calcium and Magnesium in the water are unable to form Calcium Carbonate and Magnesium Carbonate which make up hard scale. Any existing scle changes its morphology to a soft soluble substance. The interstatial spaces within scale traps biofilm and organic matter and creates harborage for pathogens. Oxcide removes these deposits and keeps the water distribution system clear.
	Challenges	Oxcide is a very mild solution of hypochlorous acid, and is very safe to handle and apply. It is NSF 60 approved for drinking water, and is OMRI listed for Organic applications. Even at 10x the recommended application dose, it has not shown any phyto-toxicity. Oxcide and all hypochlorous solutions are light and UV sensitive, and should be protected.
	Links	display » Use of hypochlorous acid for treatment of greenhouse irrigation water A brief description of the results of an experiment comparing pipes scaling and biofilm development in irrigation pipes treated with hypochlorous acid for six months to irrigation pipes left untreated. Newman, S.E. (Colorado State University) HortScience Volume 41 Issue 4
	Additional info	Capital cost is in the injection equipment, and any pre-existing proportional injection system may be used. If new proportional injection equipment is required, it is less that $1500. Treatment cost is about $1 per 1000 gallons of treated water.

Chlorine dioxide

	Tradename(s)	Ultra-Shield by Whitmire Micro-Gen Selectrocide by Selective Micro Technologies APS Dioxide by AquaPulse Systems Oxine® by Bio-Cide International
	Disinfecting action	Chlorine dioxide (ClO2) is a strong oxidizer, which differs in its water chemistry from other chlorine forms. It is particularly effective for removing biofilm as a shock treatment, or for sanitation at a continuous low rate.
	Injection method	For Ultra-Shield, a 102 gram packet is placed in a stock tank. Tablets dissolve in less than 5 minutes making a concentrated solution that can be injected into your water system. One packet of Ultra-Shield placed in a 40 gallon stock tank will produce a 50 ppm solution of Ultra-Shield. No special equipment is needed. A standard greenhouse injector is used, but check that the dilution rate is suitable. For APS Dioxide, a fully automated generator instantly produces liquid chlorine dioxide into a batch tank which may be injected in to the water system. Typically a flow based proportional injection is applied to maintain dose ratio. It may also be applied based on ppm or ORP. Oxine® can be activated with manual or fully automated systems. Followed by water or electric driven delivery systems.
	Dosage	Can be used for continuous injection or as a shock For continuous use, aim to provide a residual concentration of 0.25 ppm at water outlet. Twice a year shock treatment of lines or tanks can be applied at 20 to 50 ppm depending on product.
	Technical data	Chlorine Dioxide is typically generated by either two reactants which is 80% efficient, or 3 reactants which is 100% efficient. 2 Chemical Process 80% efficient: 5NaClO2 + 4HCI = 4ClO2 +2H2O + 5NaCl 3 Chemical Process 100% efficient 2NaClO2 + NaOCl + 2HCI = 2ClO2 +3NaCl +H2O Chlorine Dioxide Oxidation: ClO2 + 4H+ + 5e- = Cl- + 2H2O
	Monitoring	Chlorine test strips or meter. A digital colorimeter or continuous in-line chlorine dioxide monitor may also be used. For continuous injection, monitor for residual concentration of 0.25 ppm at water outlet.
	Residual effect	Provides residual control. Residual levels of the chemical is less affected by organic matter than other chlorine forms, but filtration is still recommended to reduce organic load.
	Sensitivity	Chlorine dioxide is effective at a wide pH range (4-10). Chlorine dioxide is commonly used for the removal of iron and manganese, and if these are present, then ClO2 will precipitate these out and will need to remove them with filtration. The cooler the water, the higher the solubility (post-harvest research finds toxic off-gassing at temperatures >80F, recommends maintaining water temperature at or <70F). ClO2 will also remain more in solution in enclosed irrigation lines and piping compared with open tanks and containers.
	Interaction with water quality	Chlorine dioxide is slightly acidic at the concentrations (0.25 ppm residual) recommended for continuous application.
	Challenges	Stock solutions should be used within 7 - 10 days to minimize loss due to volatilization. Use a tank with a floating lid. Potential for oxidation of micronutrients and chelates in a recirculating solution. Chlorine dioxide is sensitive to UV or direct sunlight and will breakdown, so whenever possible try to limit exposure or use UV protected injection tubing and containers.
	Links	display » Using ultra violet radiation and chlorine dioxide to control fungal plant pathogens in water Reports UV levels and chlorine dioxide concentrations needed to control some pathogens. Comments on sensitivity of UV to dissolved solids, and of chlorine dioxide to pH. Mebalds, M., A. van der Linden, M. Bankier, and D. Beardsell (Institute for Horticultural Development, AU) The Nursery Papers Volume 1996 Issue 5: 1-2 Biofilm Technical Bulletin Technical review about biofilm in the irrigation system and the use of chlorine dioxide to remove it. Khurana, K. (AquaPulse Systems) Sensitivity of Pathogens Inocula to Chlorine Dioxide Gas. Chlorine gas at relatively 25mg/L can be used to disinfect inert surfaces from Penicillium, Botrytis and Alternaria pathogens. Chastagner, G.A. and Riley, K.L. (Washington State University) Acta Horticulturae Chlorine dioxide technical bulletin Technical review of the properties of chlorine dioxide. Khurana, K. (AquaPulse Systems) KhuranaClO2.pdf Chlorine dioxide Chlorine dioxide discussion from our series on water treatment for pathogens and algae. Fisher, P.R., W.R. Argo, J. Huang, P. Konjoian, J.M. Majka, L. Marohn, A. Miller, R. Wick, and R. Yates (Water Education Alliance for Horticulture) GMPro, September 2008:14-17 Toxicity responses of herbaceous and woody ornamental plants to chlorine and hydrogen dioxides Chlorine dioxide and hydrogen dioxide are used in greenhouses for foliar disease management but can damage treated plants. This study tested the effects of different rates of chlorine and hydrogen dioxide on several ornamental plants. Copes, W.E., G.A. Chastaganer, and R.L. Hummel (USDA Small Fruit Experiment Station) Copesetal2003(toxicity).pdf Plant Health Progress Have algae met their match? Algae control can be a major challenge for greenhouse growers. This article outlines the use of chlorine dioxide to control algae. Konjoian, P. (Konjoian's Floriculture Education Services) KonjoianApril2005(algae).pdf GMPro April 2005: 49-51 Greenhouse sanitation: Too important to ignore Discusses the need for and benefits of greenhouse sanitation, and reviews some options for treating recycled water. Article begins on page 2 of linked publication. Rettke, S.K. (Ornamental IPM Program Associate, Rutgers Cooperative Research & Extension) Northeast Greenhouse IPM Notes Volume 14 Issue 7: 2-5 Activity of Chlorine Dioxide in a Solution of Ions and pH against Thielaviopsis basicola and Fusarium oxysporum Chlorine dioxide is chemically different from hypochlorites and chlorine gas. This article reports the results of experiments to determine how pH and dissolved inorganic ions affect the disinfecting activity of chlorine dioxide. Copes, W.E., G.A. Chastaganer, and R.L. Hummel (USDA Small Fruit Experiment Station) Plant Disease Volume 88 Issue 2: 188-194
	Additional info	Ultrashield: 1 gram of Ultra-Shield will make about 78.5 gallons of solution at 0.25 ppm which is the recommended constant use rate. 1000/78.5=12.74. Multiplying 12.74 times the cost of 1 gram ($0.13) gives a cost of $1.66/1000 gallons. For a nursery consuming 5,000 L water/day, capital costs estimated at $15,000; operating costs per year estimated at $400. For daily water use 100,000 L/day, numbers rise to $25,000 and $2500, respectively. AquaPulse Systems generated chlorine dioxide cost is 25 cents to treat 1000 gallons of water ($0.25/1000 gallons). Higher the water volumes lowers the cost further. Typically minimal or no capital cost since generator is supplied by APS including monitoring and injection. Oxine®: The estimated cost to treat 1,000 gallons of water at 0.5 ppm is 20 cents ($0.20/1000 gallons). The estimated cost to prepare a higher concentration (50 ppm) shock-solution is 2 cents/gallon.

Ozone

	Tradename(s)	DRAMM Corporation TrueLeaf Technologies' TrueClear Pure-O-Tech
	Disinfecting action	Changes chemical structure of organic material through oxidation-reduction reaction
	Dosage	Breaks up biofilm. 10 grams/hr per cubic meter
	Technical data	An electrical arc is used to produce the ozone from bottled or atmospheric oxygen The ozone is then bubbled through the water using a venturi injector Control of flow and pressure is required to ensure proper distribution of gas in the water stream No raw materials required, and there is no waste stream
	Monitoring	Difficult to monitor concentration directly because ozone degrades Instruments that measure concentration by stripping ozone out of water are available (In USA Inc.) Activity can be monitored by measuring pathogen load in water before and after ozone treatment
	Residual effect	Ozone degrades very quickly in water Products of degradation (peroxides, organic radicals) act as disinfectants, too, and so offer residual effect
	Challenges	Professional design of system is required to prevent ozone from escaping into atmosphere in hazardous concentrations Highly corrosive- Must use teflon tubing and stainless steel components
	Combining technologies	Often used to provide a residual effect to other disinfecting technologies (e.g. UV)
	Links	display » Pesticide removal by combined ozonation and granular activated carbon filtration Thesis work in which micropollutants (atrazine) is removed from water by using a combination of biological carbon filtration, ozone and granular activaded carbon. Orlandini, E. (Wageningen University) Ozone Ozone discussion from our series on water treatment for pathogens and algae. Hayes, C., L. Evans, P. Fisher, A. Frances, R. Vetanovetz, and Y. Zheng (Water Education Alliance for Horticulture) GMPro, Jan. 2009:16-20 Back to the basics, Part 3 In this last section of a three-part series, the use of ozone, copper and silver ionization, distillation and aeration is discussed. Roseman, J. (Aqua Ion Plus+ Technologies) Water Quality Products Volume 7 Issue 7: 16-19 Reclaim greenhouse water The need for reclaiming water, and the need for treating reclaimed water, are discussed. The article then describes a study of the use of copper ionization and ozone to control Pythium. Roseman, J. (Aqua Ion Plus+ Technologies) Water Quality Products Volume 6 Issue 10 Effect of ozone and storage temperature on two post harvest diseases and physiology of carrots (Daucus carota L.) Written from a post-harvest perspective. This article reports the results of an experiment testing the effects of ozone and storage temperature on two fungal species, including the relationship between temperature and residual ozone. Abstract available, subscription or purchase required to view full article. Liew, C.L. and R.K. Prange (Agriculture and Agri-Food Canada) Journal of the American Society for Horticultural Science 119 (3): 563-567 Water sanitation really matters: Techniques that work The presentation provides data for ozone efficacy and UV efficacy, and proposes a system where the two treatments can be used together. Fynn, R.P. and M.D. Gurol (Pure O Tech Inc.) Fynn&Gurol2007(OFApresentation).pdf OFA Shortcourse 2007

Hydrogen dioxide/activated peroxygen

	Tradename(s)	SaniDate by BioSafe Systems Xeroton-3 by Phyton Corporation ZeroTol by BioSafe Systems N.B. All of the above are EPA-registered activated peroxygen products with detailed label instructions. If using hydrogen dioxide, check with regulating authorities on legal uses.
	Disinfecting action	Hydrogen dioxide (H2O2) degrades in water, producing a very reactive oxygen molecule: 2 H2O2 --> 2 H2O + O2 Activated peroxygen products (such as SaniDate, Xeroton-3, and ZeroTol) stabilize H2O2 with acetic acid to form the strong sanitizer peracetic/peroxyacetic acid (CH3OOOH), also called PAA
	Dosage	Very product and application specific. For example, label rates range from 1 to 5400 ppm H2O2 and 1 to 200 ppm CH3OOOH (peroxyacetic acid) for activated peroxygen products. High rates are used for surface sanitation, and lower rates for continuous water treatment.
	Technical data	Liquid H2O2 solutions (35% to 50% H2O2) are injected directly into irrigation water In activated peroxygen products, a stabilized 27% H2O2 & CH3OOOH solution is injected directly into irrigation water When using as a shock treatment, solution should sit in irrigation lines at least 24 hours
	Monitoring	Test strips or other colorimetric kit to measure H2O2 or PAA (peroxyacetic acid) concentration
	Residual effect	Activated peroxygen viable up to 3 days in recycled water treatment system in the absence of significant organic matter As with other oxidants, hydrogen dioxide and PAA are rapidly broken down by organic matter in irrigation water.
	Sensitivity	Relatively insensitive to solution alkalinity
	Challenges	Activated peroxygen is a strong oxidizer and should not be mixed with any other pesticides or fertilizer
	Combining technologies	Combining with ozone would produce powerful hydroxyl radicals, but further evaluation and testing are needed Do not mix activated peroxygen with other pesticides or fertilizer
	Links	display » Controlling algae in irrigation ponds A description of the biology of algae and management strategies. Camberato, D.M. and Lopez, R.G. (Purdue University) Purdue Extension Surface sanitation: efficacy of disinfestants applied to plant production surfaces Comparison of efficacy of several chemicals including bleach, activated peroxygen (ZeroTol), quaternary ammonium chloride (Greenshield), and other products for control of Botrytis cinerea spores on different surfaces, and emphasizes that a high rate is required on porous production surfaces such as wood. W. E. Copes (USDA-ARS) 2003 SNA Research Meeting Proceedings Vole 48:212-214 Activated peroxygen (peracids/PAA) and hydrogen dioxide (hydrogen peroxide) PAA and hydrogen dioxide discussion from our series on water treatment for pathogens and algae. Larose, R., P.R. Fisher, E. Austen, V. Choppakatla, A. Frances, W.E. Horner, J. Huang, R. Wick, and R. Yates (Water Education Alliance for Horticulture) GMPro, November 2008:14-19 Toxicity responses of herbaceous and woody ornamental plants to chlorine and hydrogen dioxides Chlorine dioxide and hydrogen dioxide are used in greenhouses for foliar disease management but can damage treated plants. This study tested the effects of different rates of chlorine and hydrogen dioxide on several ornamental plants. Copes, W.E., G.A. Chastaganer, and R.L. Hummel (USDA Small Fruit Experiment Station) Copesetal2003(toxicity).pdf Plant Health Progress The reason why chlorine-treated water and peroxyacetic acid treated water register different oxidation-reduction potential (ORP) responses This article explains how ORP is determined, and why operators must draw on previous experience or historical measurements when using ORP to evaluate the effectiveness of an oxidizing agent. Howarth, J. (Enviro Tech Chemical Services) HowarthEnvTech2007(ReasonWhy).pdf Enviro Tech fact sheet 10/30/2007 Dose curves of disinfestants applied to plant production surfaces to control Botrytis cinerea Sanitation is a proven component of limiting the spread of pathogens. In this study, lethal dose curves are calculated for six disinfectants (including hydrogen dioxide, quaternary ammonium compounds, and sodium hypochlorite) applied to seven different surfaces contaminated with Botrytis. Copes, W.E (USDA Small Fruit Experiment Station) Plant Disease Volume 88 Issue 5: 509-515 Hydrogen peroxide detection with improved selectivity and sensitivity using constant current potentiometry Article describing technologies to measure hydrogen peroxide activity. Anh, D.T.V., W. Olthuis, and P. Bergveld (University of Twente, The Netherlands) Sensors and Actuators B Volume 91: 1-4

Ultraviolet (UV) radiation

	Tradename(s)	Pure-O-Tech
	Disinfecting action	Disrupts the genetic material in the cell, effectively killing it Dose, exposure time and turbidity determine effectiveness Units capable of the high flow rates often required for greenhouses are available
	Dosage	250 mJ/cm2 eliminates most pathogens 500 mJ/cm2 kills Phytophthora, Pythium, Colletotricum, and Fusarium
	Technical data	Water is exposed to high doses of UV light in tubular chambers Most common are low pressure mercury vapor lamps with a wave length of 254 nm, close to the optimum range for killing pathogens
	Residual effect	No residual effect Often used with other disinfecting material (e.g. ozone) to get some residual effect
	Sensitivity	Any particulate matter in the water disperses the light, making the UV radiation less effective Sensitive to turbidity (dissolved solids)
	Challenges	Effectiveness of lamp decreases with age; bulb should be changed regularly Bulb is housed within a quartz tube that needs to be cleaned at least every 6 months, preferably every 3 months
	Combining technologies	Good filtration is essential to remove particulate matter that would otherwise disperse the light Often used with other disinfecting agent to get residual effect (e.g. ozone)
	Links	display » Back to the basics, Part 2 In the second article of a four-part series, filtration and UV treatment are discussed. Roseman, J. (Aqua Ion Plus+ Technologies) Water Quality Products 7(6): 10-12 Using ultra violet radiation and chlorine dioxide to control fungal plant pathogens in water Reports UV levels and chlorine dioxide concentrations needed to control some pathogens. Comments on sensitivity of UV to dissolved solids, and of chlorine dioxide to pH. Mebalds, M., A. van der Linden, M. Bankier, and D. Beardsell (Institute for Horticultural Development, AU) The Nursery Papers Volume 1996 Issue 5: 1-2 Disinfection of Nutrient Solution in Closed Soilless Systems in Italy An efficacy comparison of sand filtration, UV radiation, Na dichloroisocianurate, and metalaxyl on Phytphthora cryptogea on Gerbera plants. By the end of the season, the best control was observed with metalaxyl, followed by sand filtration and U.V. radiation with a 97, 84, and 76% disease control compared to the untreated plants, respectively. Garibaldi, A., Minuto, A. and Salvi, D. (Di. Va.P.R.A. Plant Pathology Department) Acta Horticulturae Ultraviolet light Ultraviolet light discussion from our series on water treatment for pathogens and algae. Fynn, R.P., P. Fisher, A. Frances, and W.R. Argo (Water Education Alliance for Horticulture) GMPro, Feb. 2009:16-21 Methods to control Pythium and Phytophthora in cold plastic houses In this study, sodium hypochlorite and UV ares used to treat water infested with Pythium and Phytopthora. Sodium hypochlorite reduced plant mortality, but the best plant health was observed when the water was not infested with pathogens in the first place. Berenguer, J.J., I. Escobar, and M. Garcia (Estacion Experimental, La Nacla, Granada) Berengueretal2001ActaHort(Pyth&Phyt_cold_plastic_houses).pdf Acta Horticulturae Volume 559: 759-763 Water sanitation really matters: Techniques that work The presentation provides data for ozone efficacy and UV efficacy, and proposes a system where the two treatments can be used together. Fynn, R.P. and M.D. Gurol (Pure O Tech Inc.) Fynn&Gurol2007(OFApresentation).pdf OFA Shortcourse 2007

Copper ionization

	Tradename(s)	AquaHort Superior Aqua
	Disinfecting action	Copper ions (Cu2+) are toxic to most pathogens, incl. Pythium, Phytophthora, Xanthomonas, and algae
	Dosage	0.5 to 1 ppm Cu for pathogens 1 to 2 ppm for algae and biofilm
	Technical data	An electrical charge is passed between copper bars or plates in the water stream, releasing copper ions into the water The amount of Cu2+ released is proportional to the electrical current The lower the EC, the larger the copper surface needs to be Choose a copper ionization system that automatically adjusts the Cu2+ output for flow rate and EC
	Monitoring	Electrodes, colorimetric meters, and kits are available for measuring Cu2+ concentration
	Residual effect	Offers residual control
	Sensitivity	EC affects copper ion output; choose a copper ionization system that automatically adjusts for EC Relatively resistant to being absorbed by organic material in the water At pH 7, copper ions can precipitate
	Challenges	The applied copper concentrations are a fraction of plant toxicity levels, and problems have not been reported Many growers use copper ionization on sensitive crops (e.g. propagation of cuttings and seedlings) Copper toxicity has been observed using copper sulfate in hydroponic systems Until more research is completed, caution is prudent
	Links	display » Copper ionization Copper ionization discussion from our series on water treatment for pathogens and algae. Fischer, R., P. Fisher, and A. Frances (Water Education Alliance for Horticulture) GMPro, Dec. 2008:18-21 The effect of silver and other metal ions on the in vitro growth of root-rotting Phytophthora and other fungal species Tests the toxicity of a range of ions to Phytophthora, and finds that copper to be of relative high toxicity, second only to silver. Note that this article focuses primarily on silver. Slade, S.J. and G.F. Pegg (University of Reading, UK) Annals of Applied Biology Volume 122: 233-251 Sensitivity to copper and phosphite of Phytophtora species associated with ink diseases of chestnut Reports an experiment to determine the toxicity of copper ions to Phytopthora in chestnut. Inhibition of Phytophthora growth increased with increasing copper concentrations. Chelho, V., S. Coutinho, and M.E. Gouveia (Instituto Politecnico de Braganca, Portugal) Acta Horticulturae Volume 693: 641-643 Back to the basics, Part 3 In this last section of a three-part series, the use of ozone, copper and silver ionization, distillation and aeration is discussed. Roseman, J. (Aqua Ion Plus+ Technologies) Water Quality Products Volume 7 Issue 7: 16-19 Response to copper toxicity for three ornamental crops in solution culture Tests to determine level where phytotoxic responses to copper become apparent in three ornamental crops. Zheng, Y., L. Wang, and M. Dixon (University of Guelph, Canada) HortScience Volume 39 Issue 5: 1116-1120 Greenhouse pepper growth and yield response to copper application Tests for phytotoxic responses to copper in young and old hydroponically grown pepper plants. Zheng, Y., L. Wang, and M. Dixon (University of Guelph, Canada) HortScience Volume 40 Issue 7: 2132-2134 Reclaim greenhouse water The need for reclaiming water, and the need for treating reclaimed water, are discussed. The article then describes a study of the use of copper ionization and ozone to control Pythium. Roseman, J. (Aqua Ion Plus+ Technologies) Water Quality Products Volume 6 Issue 10 Hygiene in the nursery: Disinfecting production surfaces; cement, gravel, capillary mats and sand beds Advice and guidelines for sanitizing porous surfaces in the greenhouse. Tested efficacy of copper ionization, chlorination, and quaternary ammonium compounds against fungi, bacteria, and nematodes on several different surfaces. Stovold, G. (Tropical Fruit Research Station, Alstonville, AU) The Nursery Papers Volume 2000 Issue 5: 1-4

Heat Treatment/Pasteurization

	Disinfecting action	Pathogen resistance to heat varies. Effect largely independent of water quality.
	Injection method	Water is heated to specific temperature, and waste heat is recovered to pre-heat incoming water.
	Dosage	An example treatment is 203ºF for 30 sec. No residual effect on pathogens downstream of treatment.
	Additional info	High energy use makes it expensive for large flow. To prevent scaling of heat exchangers from hard water, pH needs to be reduced to 4.5, then raised again as needed for irrigation. Best for low flow - high sanitation applications.