Managing Algae in the Greenhouse
October 2006

The greenhouse provides an ideal environment for the growth of algae. Algae are primitive plants without true roots, leaves and stems that contain chlorophyll.  Algae growth on greenhouse floors and walkways, under benches and in pots 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. It is a food source for shore flies and fungus gnats.  Excessive growth on walkways is a safety hazard to workers. Growth of algae on greenhouse coverings reduces light levels in the greenhouse. Algae clogs irrigation lines, misting lines and emitters.

Sanitation, environmental modification, and the routine use of algicides are all needed to manage algae.

Prevention and Sanitation
Keep greenhouse floors free of plant debris, spilled potting media and weeds that are a source of nutrients for the growth of algae. Using porous concrete floors and sand in construction helps limit the development of excess moisture in the greenhouse. Houses with dirt or gravel floors tend to retain moisture for long periods of time favoring the growth of algae. Using a weed block fabric on the greenhouse floor helps to prevent both weed and algae growth.

Environmental Modification
Proper ventilation is also needed to reduce the amount of moisture in the greenhouse. Horizontal airflow fans and environmental computer controls help to regulate greenhouse temperatures and reduce excess condensation.

Follow Proper Watering Practices
Training employees on proper watering practices is crucial. Over watering of crops with constant moisture frequently leads to algae and liverwort buildup on the surface of the growing media. Avoid over watering crops, especially early in the crop cycle, so that the upper surface of the media is able to dry out between watering. 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 greenhouse 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 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.

 

Chlorine Dioxide

A chlorine dioxide-generating product (Selectrocide ™12G) 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. A 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.

 

Hydrogen Dioxide

Hydrogen dioxide (ZeroTol ® and Oxidate ®) are labeled as disinfectants for use on greenhouse surfaces, equipment, benches, pots and trays. 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.

 

Sodium Carbonate Peroxyhydrate

Sodium carbonate peroxhydrate (GreenClean® 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® 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. 

 

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.	Manufacturer	REI
Chlorine Dioxide	Selectrocide ™12G	74986-5	Selective Micro Technologies
Hydrogen Dioxide	Oxidate®	70299-2	BioSafe Systems LLC	0 1 (spray)
Hydrogen Dioxide	ZeroTol®	70299-1	BioSafe Systems LLC	0
Quaternary Ammonium Compound	Green-Shield®	499-368	Whitmire Micro-Gen
Quaternary Ammonium Compound	Physan 20®	55364-5	Maril Products, Inc.	12 (plants) 0 (hard surface)
Quaternary Ammonium Compound	Triathlon™	58044-3-59807	OHP
Sodium Carbonate Peroxyhydrate	GreenClean®	70299-4	BioSafe Systems LLC	0 1 (spray)

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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.griffins.com/selectrocide or www.selectivemicro.com
Hydrogen Dioxide	Oxidate® ZeroTol®	Use on greenhouse structures, benches, and walkways.	0.5 fl. oz - 2.5 fl. oz.	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 Compound	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 Compound	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 Compound	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 ®	Use on walkways, weed control 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.

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.
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.

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