Moss is a fairly common and often unwanted type of vegetation that may become an annoyance or damaging agent on lawns, roofs or other structures. The active ingredient in moss killers designated for use on lawns is usually an iron-containing or soap salt product. Moss killers used to eliminate moss on roofs or structures where desirable vegetation will not be affected often contain some form of zinc, soap salts or acid.
Zinc sulfate in the form of zinc sulfate monohydrate is the active ingredient in some moss killers used to treat moss on roofs or structures. This chemical does not corrode galvanized gutters or aluminum or stain roofs. It can be applied directly to moss as a powder or mixed with water and sprayed. Zinc sulfate is toxic to fish and aquatic invertebrates, and it may damage any plants with which it comes in contact.
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Soap salts are either potassium or ammonium salts of fatty acids. These products are suitable for moss control in grass and on roofs or other structures such as decks and sidewalks. Moss-killing products with soap salts are noncorrosive, will not stain most surfaces and will not harm vegetation. Soap salts such as potassium salts of fatty acids are available in liquid form under a number of brand names. Soap-based products offer the added benefit of cleaning surfaces as they kill moss. Although these products are biodegradable, direct runoff into water sources may harm aquatic invertebrates.
Zinc chloride, as with zinc sulfate, will negatively impact any vegetation, fish or aquatic invertebrates it comes in contact with. Zinc chloride is commercially available in different concentrations, so be sure to follow the label directions and dilute it if necessary. Zinc chloride is sold as a liquid to be sprayed onto moss-covered structures. This chemical will damage copper fixtures.
Acid-based Moss Killer
Acid-based moss killers, as with soap salt–based moss killers, are among the least toxic moss killers. Acids in moss killers are generally citric or acetic acids. Acid-based products may stain or lighten surfaces and damage metallic surfaces. As with all other moss killers, products that contain acid should not be allowed to run off directly into water.
Iron-based moss killing products may contain iron in one of the following forms: ferrous sulfate anhydrous, ferric sulfate, iron sulfate or ferrous sulfate monohydrate. Iron-based products, as with soap salt products, are suitable for moss control in lawns. Some iron-based products are highly irritating to the skin and eyes and may stain cement surfaces, so use these moss killers with extreme caution.