After fall production is done, take time to properly disinfect/disinfest your greenhouses. Propagation houses in nurseries should be disinfected/disinfested sometime between propagation cycles during the year. The following are some disinfectants for use in the greenhouse. Information is from the University of Massachusetts.
There are several different types of disinfectants that are currently used in the greenhouse for plant pathogen and algae control. They are quaternary ammonium compounds (Green-Shield®, Physan 20®, and Triathlon®), hydrogen dioxide (ZeroTol®, Oxidate®), chlorine dioxide (SelectrocideT) and chlorine bleach. Alcohol, although not used as a general disinfectant is mentioned here because it is used by growers to disinfect propagation tools. All these products have different properties. If possible, disinfectants should be used on a routine basis both as part of a pre-crop clean-up program and during the cropping cycle.
Organic growers have limited options for disinfectants. Oxidate® is the only material mentioned above that is currently listed by the Organic Material Review Institutes (OMRI), see www.omri.org . Ethyl or isopropyl alcohol is also allowed under the organic standards. Organic growers should always check with their certifying organization before using any material new to their farming practices.
Quaternary ammonium chloride salts (Green-Shield®, Physan 20® and Triathlon®).
Q-salt products, commonly used by growers are quite stable and work well when used according to label instructions. Q-salts are labeled for fungal, bacterial and viral plant pathogens, and algae. They can be applied to floors, walls, benches, tools, pots and flats as disinfectants. Physan 20® is also labeled for use on seeds, cut flowers and plants. Carefully read and follow label instructions. Recommendations may vary according to the intended use of the product. For example, the Green-Shield® label recommends that objects to be sanitized should be soaked for 10 minutes, and walkways for an hour or more. Instructions recommend that surfaces be air-dried after treatment except for cutting tools. The label recommends soaking cutting tools for 10 minutes before use, then using the wet tool on plants. One way to do this is by having two cutting tools, one pair to use while the other is soaking.
Q-salts are not protectants. They may eradicate certain pathogens, but will have little residual activity. Contact with any type of organic matter will inactivate them. Therefore, pre-clean objects to dislodge organic matter prior to application. Because it is difficult to tell when they become inactive, prepare fresh solutions frequently (twice a day if in constant use). The products tend to foam a bit when they are active. When foaming stops, it is a sign they are no longer effective. No rinsing with water is needed.
Hydrogen Dioxide (ZeroTol®, OxiDate®)
Hydrogen dioxide kills bacteria, fungus, algae and their spores immediately on contact. It is labeled as a disinfectant for use on greenhouse surfaces, equipment, benches, pots, trays and tools, and for use on plants. Label recommendations state that all surfaces should be wetted thoroughly before treatment. Several precautions are noted. Hydrogen dioxide has strong oxidizing action and should not be mixed with any other pesticides or fertilizers. When applied directly to plants, phytotoxicity may occur for some crops, especially if applied above labeled rates or if plants are under stress. Hydrogen dioxide can be applied through an irrigation system. As a concentrate it is corrosive and causes eye and skin damage or irritation. Carefully read and follow label precautions. Note that OxiDate® is the only product of the products mentioned in this article listed on the Organic Material Review Institutes (OMRI) website, in the newly-listed products section.
Sodium Carbonate Peroxyhydrate (GreenClean Granular Algaecide®, TerraCyte®)
Both algaecides are granular and activated with water. Upon activation, sodium carbonate peroxhydrate breaks down into sodium carbonate and hydrogen peroxide. GreenClean is labeled for managing algae in any non-food water or surfaces. TerraCyte in addition to being an algaecide is labeled to control moss, liverworts, slime, molds and their spores and is labeled for use on plants. Non-target plants suffer contact burn if undiluted granules are accidentally spilled on them.
Chlorine Dioxide (SelectrocideT)
Chlorine dioxide is a new disinfectant in the horticulture industry for controlling algae, bacteria, viruses, fungi and other microbial pests on greenhouse surfaces and in greenhouse irrigation systems. Currently it is labeled to be used to clean out irrigation lines with a periodic treatment at a moderate dose or to keep lines from becoming re-contaminated by treating irrigation water flowing through the system with a continuous ultra-low dose. Research continues to be conducted on this product to expand its use in the industry.
Chlorine bleach.
There are more stable products than bleach to use for disinfecting greenhouse surfaces. Chlorine bleach may be used for pots or flats, but is not approved for application to walls, benches or flooring. When used properly, chlorine is an effective disinfectant and has been used for many years by growers. A solution of chlorine bleach and water is short-lived and the half-life (time required for 50 percent reduction in strength) of a chlorine solution is only two hours. After two hours, only one-half as much chlorine is present as was present at first. After four hours, only one-fourth is there, and so on. To ensure the effectiveness of chlorine solutions, it should be prepared fresh just before each use. The concentration normally used is one part of household bleach (5.25 percent sodium hypochlorite) to nine parts of water, giving a final strength of 0.5 percent. Chlorine is corrosive. Repeated use of chlorine solutions may be harmful to plastics or metals. Objects to be sanitized with chlorine require 30 minutes of soaking and then should be rinsed with water. Some would say that rinsing is not necessary. Bleach should be used in a well-ventilated area. It should also be noted that bleach is phytotoxic to some plants, such as poinsettias.
Alcohol (70 percent) is a very effective sanitizer that acts almost immediately upon contact. It is not practical as a soaking material because of its flammability. However, it can be used as a dip or swipe treatment on knives or cutting tools. No rinsing with water is needed.
Disinfectants should be used on a routine basis both as part of a pre-crop clean up program and during the cropping cycle.
Reprinted from Cleaning and Disinfecting the Greenhouse by Tina Smith, Extension Educator, Floriculture Program, Dept. Plant, Soils and Insect Sciences, University of Massachusetts, Amherst. http://www.umass.edu/umext/floriculture/fact_sheets/greenhouse_management/ghsanitz.html
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