As Indiana growers finish up the 2017 season, it is important to remember to clean and sanitize equipment and tools. In this article, I would like to discuss the importance of and how to sanitize.
Bacteria and fungi that cause plant disease may survive on some types of equipment. Examples include: stakes, transplant trays, shovels, greenhouse benches etc.
Equipment can be contaminated by diseased plants in close contact with the surfaces. For example, a tomato with bacterial canker may rub up against a wooden stake, transferring some of the bacteria to the stake. Such bacteria may cause disease problems next year. A transplant tray of cantaloupe with a damping-off problem may have the same disease next year if the tray is not properly cleaned and sanitized.
It is important to clean the equipment of crop debris or soil prior to the use of one of the sanitizers described below. Equipment free of crop debris and soil is less likely to harbor disease. However, the use of a sanitizer helps to kill any pathogens that remains after cleaning.
This article will discuss 3 types of sanitizers: sodium hypochlorite, hydrogen dioxide, and quaternary ammonium.
Sodium hypochlorite – this is common household bleach. The advantage of bleach is that it is easy to obtain and relatively cheap to purchase. The disadvantage of bleach is that sodium hypochlorite is easily deactivated by sun and organic matter. When the solution becomes dirty with organic matter, it needs to be changed. Normally, bleach solutions should be changed after about 2 hours of use. See detail below regarding use rates.
Hydrogen dioxide – products with this active ingredient include Oxidate® and Zerotol®. Hydrogen dioxide is similar to hydrogen peroxide, which is used as a skin disinfectant (do not use hydrogen peroxide for agricultural uses). The labels I have for Oxidate®, Oxidate 2.0® and Zerotol 2.0® discuss the use of these products for sanitizing hard, non-porous surfaces. That would seem to exclude use on wooden stakes. However, the labels for Oxidate 2.0® and Zerotol 2.0® also describe the use of foaming applications for porous surfaces by the use of surfactant foaming agents. Both Oxidate 2.0® and Zerotol 2.0® have 2% peroxyacetic acid in addition to hydrogen peroxide. Do not store mixes of any of these products for use the next day.
Quaternary ammonium – Products with this active ingredient include Green-Shield® and Physan 20®. These products have identical active ingredients. The label for both products states that surfaces should remain wet after application for at least 10 minutes regardless of application method. Solutions should be prepared daily or re-mixed when solution becomes visibly dirty. This is good advice for all three of the sanitizers discussed here. The Physan 20® label clearly states that it should only be used for non-porous surfaces. The Physan 20® label also states, “Not intended for use in domestic greenhouses where food crops are grown”. I think this means not to use Physan 20® in homeowner greenhouses for food crops.
All three of the sanitizer products described here must be diluted before use. That is, don’t use any of these products straight out of the bottle.
Hydrogen dioxide and quaternary ammonium products have clear use directions for dilution and application. These products also have Worker Protection Standards (WPS) for what to wear during applications. Follow these directions carefully.
It may be more difficult to interpret the bleach label for use in agricultural situations. I recommend the rate listed under “Sanitizing work surfaces”, 2 tsp (1/3 fl oz) per gallon of water. This works out to 200 ppm available chlorine. WPS requirements for the use of bleach in an agricultural situation are not listed on the bottle. However, I recommend using similar requirements as are listed for the hydrogen dioxide and quaternary ammonium products: coveralls worn over long-sleeved shirt and long pants; waterproof gloves (the long chemical resistant kind); chemical-resistant footwear and socks; protective eyewear (goggles or face mask); chemical-resistant apron when mixing. Bleach is usually available in gallon jugs of 8.25% sodium hypochlorite. Note that old bottles of bleach may lose activity. Test kits are available to test sodium hypochlorite activity.
For most uses, I recommend the use of either the hydrogen dioxide and quaternary ammonium products. These products should have more activity longer in solution than bleach.
Although it may seem like a lot of trouble now, cleaning and sanitizing equipment will save time and money in the long run.