Managing Algae in the Greenhouse
Dec 2010

Algae are primitive plants lacking true roots, leaves and stems that contain chlorophyll.  The greenhouse provides an ideal environment for the growth of algae.

Algae growth on walkways, under benches and in pots or plugs is a problem for many growers

Algae compete with desirable plants for nutrients and form an impermeable layer on the media surface that can interfere with water penetration. During plug production, slower –growing plants can be especially sensitive to algae buildup.  Algae are  a food source for both shore flies and fungus gnats.  Excessive growth on walkways is a safety hazard to workers. Growth of algae on greenhouse coverings can also reduce light levels in the greenhouse. Prevention measures include sanitation, environmental modification, and the frequent  use of disinfectants.  

Prevention

Sanitation
All surfaces should be kept free of plant debris and weeds that can be a nutrient source for the growth of algae.  A physical weed mat barrier helps to prevent both weed and algae growth..

Environmental Modification
Proper ventilation  reduces the amount of moisture in the greenhouse. Horizontal airflow fans help  regulate greenhouse temperatures and reduce excess condensation. Retractable roof or open roof greenhouses provide superior ventilation benefits.

Proper Watering Practices
Train employees on proper watering practices. . Over watering crops  frequently leads to algae and liverwort buildup on the surface of the growing media. Avoid over watering crops, especially early in the crop cycle, to allow   the upper surface of the media to dry out in  between waterings. Select a growing media with the appropriate drainage for your crops. Water the containers only as needed, to prevent excess puddling of water on the  floor.

Avoid excessive fertilization, runoff and puddling water on floors, benches and greenhouse surfaces to discourage algae growth. The use of porous concrete floors limits the development of excessive moisture in the greenhouse. The greenhouse floor should be level and drain properly to prevent the pooling of water.

Disinfectants and Algicides  
A number of disinfectants and algicides are currently registered for algae control in the greenhouse. (See Table 1)

Disinfectants should be used on a routine basis as part of a precrop clean- up program and during the cropping cycle. Disinfectants such as chlorine dioxide,  quaternary ammonium compounds, hydrogen dioxide and sodium carbonate peroxyhydrate may be used.  

Controlling Existing Algae

Chlorine Dioxide
A chlorine dioxide-generating product (Selectrocide ™12 G) produces a solution of chlorine dioxide in water that can be injected into irrigation lines to remove algae and the bioslime surrounding the algae. At higher rates, it can be used as a shock treatment to clean out irrigation lines. This shock treatment solution should not be used to irrigate crops, because of potential phytotoxicity, and it should be done between crops. An ultra-low rate can also be continuously used to inhibit the reemergence of algae.  

Quaternary Ammonium Compounds
Quaternary ammonium compounds include Green-Shield®, Physan 20®, and Triathlon®. They can be applied to floors, walls, benches, tools, pots and flats as disinfectants. Before using these quaternary ammonium compounds, pre-clean all surfaces. Contact with any type of organic matter inactivates these compounds. Surfaces should remain thoroughly wet for at least 10 minutes. A fresh solution should be applied daily or when the solution becomes visibly dirty.

A fourth generation quaternary ammonium product (KleenGrow™) has higher organic tolerances and longer residual activity on hard surfaces. It can also be applied through drip irrigation systems or flood systems. However, if applied too frequently, KleenGrow™ can be phytotoxic to plant material and cause stunting.

Hydrogen Dioxide
Hydrogen dioxide (Oxidate® and ZeroTol ® are labeled as disinfectants for use on greenhouse surfaces, equipment, benches, pots and trays. Oxidate® is an organic product. All surfaces should be thoroughly wetted before treatment. ZeroTol® and Oxidate® are also labeled for use in chemigation.

Several precautions are noted on their labels. Hydrogen dioxide is a strong oxidizing agent and should not be mixed with any other pesticides or fertilizers. When applied directly to plants, phytotoxicity may be of concern, for some crops, especially if applied above labeled rates or if plants are under stress.

Hydrogen Peroxide & Peroxyacetic Acid
Hydrogen Peroxide & Peroxyacetic Acid (Sanidate®) is also labeled as a disinfectant for use on greenhouse surfaces and equipment, pots, trays, and walkways.  Is is also labeled for use in greenhouse irrigation systems.

Hydrogen Peroxide, Peroxyacetic Acid and Octanoic Acid
Hydrogen peroxide & peroxyacetic acid & octanoic acid (Xeroton -3™) is a strong oxidizing agent. It may be used as an algaecide on greenhouse structures, floors etc.  For best results, use with water with a neutral pH and low levels of organic materials.  Do not use at higher than recommended rates or leaf burn may result.  It is advisable to test Xeroton -3™ on a few plants before treating large numbers.  Care should be taken when applying Xeroton -3™ as a foliar spray following applications of metal based products.  It is also labeled for use in chemigation.

Sodium Carbonate Peroxyhydrate
Sodium carbonate peroxhydrate (GreenClean Pro ® Granular algicide) is labeled for algae control in greenhouses. Treat when growth first begins to appear. Effects of treatment are immediately apparent (bubbling, bleaching and discoloration of algae).  

GreenClean Pro® is water activated. Upon contact with water, sodium carbonate peroxhydrate breaks down into sodium carbonate and hydrogen peroxide. Non- target plants suffer contact burn if undiluted granules are accidentally spilled on them. 

Sodium carbonate peroxyhydrate (TerraCyte®) is labeled for the prevention and control of algae, moss, and liverworts. Terracyte® is also water activated. Several precautions are noted on the TerraCyte® label. First test a small section of ornamental plants at labeled rates for potential phytotoxicity before large-scale use in containers. Phytotoxicity may occur on sensitive crops. Thoroughly rinse granules of foliage to prevent contact burn. Repeat applications can raise soil pH to levels that can adversely affect plant growth. TerraCyte® is incompatible with metal-based fungicides and fertilizers.  

Table 1. Algicides labeled for use in a greenhouse
If any information in this table is inconsistent with the label, follow the label.
By law, in order to use a pesticide product, it must be registered in the state.

Common Name	Trade Name	EPA Reg. No.	Toxicity	Manufacturer	REI (hrs)
Chlorine Dioxide	Selectrocide ™12G	74986-5	D	Selective Micro Technologies
Hydrogen Dioxide	Oxidate®	70299-2	D	BioSafe Systems LLC	0 1 (spray or fog)
Hydrogen Dioxide	ZeroTol®	70299-1	D	BioSafe Systems LLC	0
Hydrogen peroxide & peroxyacetic acid & octanoic acid	Xeroton-3™	49538-4	D	Phyton Corporation	2(fogging) 0
Quaternary Ammonium	Green-Shield®	499-368	D	Whitmire Micro-Gen
Quaternary ammonium	KleenGrow™	81820-2	D	Pace 49 Inc.	0 (hard surface)
Quaternary Ammonium	Physan 20®	55364-5	D	Maril Products, Inc.	12 (plants) 0 (hard surface)
Quaternary Ammonium	Triathlon®	58044-3-59807	D	OHP
Sodium Carbonate Peroxyhydrate	GreenClean Pro®	70299-6	D	BioSafe Systems LLC	0 1 (spray)
Sodium carbonate peroxyhydrate	TerraCyte®	70299-3	D	Biosafe Systems LLC	4

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Table 2: Algicides and their characteristics
If any information in this table is inconsistent with the label, follow the label.
By law, in order to use a pesticide product, it must be registered in the state.
 

Common Name	Trade Name	Target Application	Rate/1 gal	Comments
Chlorine Dioxide	Selectrocide™ 12G	Chemigation		See label and technical bulletin at  www.selectivemicro.com
Hydrogen Dioxide	Oxidate® ZeroTol®	Use on greenhouse structures, benches, and walkways.	See labels	Strong oxidizing agent. Works by surface contact. All surfaces need to be thoroughly wet before treatment. Use higher rate if areas are not pre-cleaned with water to remove organic deposits. See label for information on chemigation. See label for specific plant applications. Do not use at higher than labeled rates as leaf burn may result.
Quaternary Ammonium t	Green–Shield®	Use on greenhouse glass or walkways	0.16 fl. oz. – 0.5 fl. Oz (1 tsp. – 1 Tbsp.)	Use higher rates on walkways. For heavy infestation, let stand for an hour or more. Brush and wash away dead algae. Soak area again.
Quaternary Ammonium	Physan 20®	Use on greenhouse glass and walkways	0.16 fl. oz.- 0.5 fl. oz. (1 tsp.- 1 Tbsp.)	Use higher rates on walkways. Preclean all surfaces. Thoroughly wet all surfaces for at least ten minutes. Fresh solution must be applied daily or when visible solution becomes dirty. Not for use in greenhouses where food crops are grown. See label for specific plant applications.
Quaternary Ammonium	Triathlon®	Use on   greenhouse surfaces and walkways.	0.25 fl. oz. (1.5 tsp.)	Wet treated area thoroughly and allow it to remain wet for ten minutes. For heavy algae growth, let stand one hour, wash off algae and reapply.  Repeat applications whenever algae growth returns.
Sodium Carbonate Peroxyhydrate	GreenClean Pro®	Use on walkways, and weed mats under benches.	See label for rates.	Strong oxidizing agent. Treat when algae growth first begins to appear. Non-target plants will suffer contact burn if undiluted granules are accidentally spilled on them. Make granular applications over a wet surface or activate with water immediately following application.
Sodium carbonate peroxyhydrate	TerraCyte®	Use on walkways and under benches	See label	Strong oxidizing agent. See label for specific precautions for plant applications.
Hydrogen peroxide & peroxyacetic acid & octanoic acid	Xeroton -3™	Use on greenhouse structures, and walkways. Chemigation	See label	Clean surfaces before treatment. Allow solution to remain wet for 10 minutes. Reapply as needed for control/
Quaternary ammonium compound	KleenGrow™	Use on greenhouse surfaces & walkways	0.125-0.25 fl. Oz.	Thoroughly clean all surfaces, and saturate for 10 minutes. Ventilate closed spaces. Reapply every 14 days to keep algae from returning.

Leanne Pundt, Extension Educator, Commercial Horticulture, University of Connecticut

References:
Chase, A. R and C. A Conover. 1993. Algae Control in an Ebb and Flow Irrigation System. Proc. Fla. State. Hort. Soc. 106:280-282.
Grey, D. 2000. Controlling Algae in Plug Production. GrowerTalks. September 2000. pp. 92.

Konjoian, P. 2005. Algae: Choking Profits from My Greenhouse. Grower Talks. 68-72
Powell, C. 2000. Disease Doctor- How can algae buildup on porous surfaces in greenhouses be removed? Greenhouse Business. August 2000. pp. 41
Powell, C. 1999. Disease Doctor- What to do about this "green stuff." Greenhouse Business. December 1999. pp. 37

Information on our site was developed for conditions in the Northeast. Use in other geographical areas may be inappropriate.

Information on our site was developed for conditions in the Northeast. Use in other geographical areas may be inappropriate.

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