Chemical
Moss Control for Roofs, Decks, and Sidewalks
Zinc strips
| Potassium salts | zinc
sulfate | zinc chloride | zinc-copper
| bleach
Zinc
Strips
General Information:
Zinc strips are usually considered
the long-term solution to controlling mosses (see photo at right: skylights are surrounded
by galvanized flashing that has suppressed the growth of mosses
below the skylights. The remaining parts of this cedar shake roof
are covered mainly with the moss Dicranoweisia. Zinc
strips and galvanized flashing are apparently relatively safe
and inexpensive. They effectively kill or retard the growth of
mosses and fungi and appear to have effect up to 15 feet below
the zinc flashing along the length of the flashing. To use:
apply the rolled zinc or galvanized flashing to each side of ridge
caps along the roof peaks. Nail at one foot spacings along
the zinc strip. With each rain zinc is released from the
strip and kills the mosses below the strip. For best results
remove the existing mosses prior to treatment. The active ingredient
is metallic zinc.
Effectiveness: Zinc strips can be effective
for many years. The effect of galvanized
flashing (example above) can persist for decades. Success rates
vary with the degree of moss development and weather. Zinc
strips or flashing are most effective before mosses are well developed.
Physical removal of existing moss followed by installation of
zinc strips or flashing is an effective long-term strategy for
suppressing moss growth.
Negative Side
Effects: Direct runoff from
the zinc strips or flashing to surrounding vegetation, fish ponds,
or water supplies should be avoided, because some contamination
by zinc is likely to occur. Zinc strips should not be used with
strong acids or bases.
Possible Alternatives: Consider periodic physical control.
Potassium
salts of fatty acids
General Information: This product is non-staining on most surfaces
and is for use on decks, fences, roofs and lawns. This product
will supposedly not harm bordering plants. This product is made
from biodegradable fatty acids. It
is water based. non-corrosive to metals, and contains no zinc or
iron. This product is available in liquid form in several brands.
One brand is Safer. To apply this
product, attach bottle to hose and spray liberally over infected
area.
Effectiveness: Many people have reported varying degrees
of success with the use of potassium salt products. Experimental
trials on Racomitrium on old asphalt resulted in very little
kill, even at concentrations well above the recommended dose (Ash 1999).
Negative Side
Effects: Because this product
occurs naturally in the environment and is biodegradable the environmental
side effects are presumed to be small. This product is toxic to aquatic invertebrates.
These products should not be applied directly to water and should not
come into contact with water sources.
Possible Alternatives: Before treating mosses one should consider
whether it is necessary to treat the mosses or not. Please see
our site on whether or not to control mosses as well as the page
related to applying bleach to mosses.
Zinc
Sulfate
General Information: The active ingredient for some moss killers
is zinc sulfate monohydrate usually at concentrations of 99%.
One brand name is Moss B Ware. According to the manufacturers, zinc sulfate will not stain roofs
or corrode aluminum and galvanized gutters. To use zinc
sulfate one can apply powder directly to moss areas. Manufacturers
recommend that powder should be applied thoroughly - for
example, up to three pounds for every 600 square feet. For
spraying combine three pounds to five gallons of water and apply
to 600 square feet. This product should be applied on
a calm day.
Effectiveness: Powder application
has been known to control mosses for two years and spraying application
may need to be applied annually. Some roofing companies will guarantee
no rooftop mosses for up to five years after using this product.
Negative Side
Effects: This product is
toxic both to fishes and aquatic invertebrates. Zinc sulfate
should not be applied to water. If zinc sulfate comes into
contact with neighboring plants, damage may occur. Plants
and shrubbery should be draped when this chemical is being used.
Possible Alternatives: Alhough this product is effective in controlling
mosses, it is not entirely environmentally safe or smart.
Consider the need to control -- is there
a different perspective or solution to your moss problem without
polluting the environment?
Zinc
Chloride
General Information: Zinc chloride comes in two different concentrations,
13% and 62%. The 13% concentration can be applied directly
to moss without mixing with water. According to manufacturer instructions, spray directly from a nozzle
six to ten inches away from target. Make sure to wet the area
thoroughly. The 62% concentration should to be mixed with water
before applying to an affected area. Mix one pint of concentration
to three gallons of water. Using a backpack sprayer, one
manufacture recommends using one gallon for every 100 sq ft. Zinc
chloride should be applied just prior to fall rains or in the
early spring.
Effectiveness: Zinc chloride is effective in controlling
mosses from one year up to five years. Increased application
concentrations may be needed in areas of higher moss concentration.
Negative Side
Effects: Avoid drift and
runoff when using this product. Zinc chloride will affect
other plants and lawns. Application should only take place when
air is still and when no rain is expected within 24 hours. Zinc
chloride is corrosive and should not be used when copper fixtures
are present. This product is toxic to fishes and aquatic
invertebrates. Avoid contaminating water sources with zinc chloride.
If zinc chloride comes into contact with a painted area damage
is possible.
Possible Alternatives: Considering the toxicity of this chemical,
it may be possible to use a less corrosive and less dangerous
product. Please see other chemicals on this web site as
well as considering reasons to control or
not.
Zinc
- Copper sulfate mix
General Information: Zinc and copper sulfate comes dry, but can
be applied as a powder or mixed with water. This product
reacts electrolyticallly with water to stimulate a slow release
reaction. Zinc and copper sulfate will not stain patios,
decks, walls, walkways, buildings or roofs. However, zinc
and copper sulfate may react with red bricks. This product
is not harmful to lawns, ornamental shrubs, trees, turf or other
vegetation such as flowers and vegetation. To apply simply
sprinkle areas thoroughly with powder when it is wet, either after
a rain or when early morning dew is present. Do not use
this product in high wind. For spray application a wet applicator
may need to be purchased. It is not clear if this product is still
available commercially. According to information from one manufacturer,
apply one pound of moss killer to 1000 sq ft. This product
may be applied anytime during the year, but should not be applied
while it is raining. Since this product specializes in the
slow release reaction; allow plenty of time for the chemical to
act. This product is corrosive and should not be used if copper
fixtures are present.
Effectiveness: Applications of zinc and copper sulfate
are said to last for up to one year depending on the concentrations
of moss. Annual application is generally needed.
Negative Side
Effects: Though this product
is supposedly safe for surrounding plants, it is toxic to fishes
and aquatic invertebrates. Do not apply this product to
water or let the product come into contact with water sources.
When applying this product or any product to rooftops it is essential
to avoid runoff. Collecting the runoff in a fashioned trap would
greatly reduce the negative effects on the environment.
Possible Alternatives: Based on the manufacturer's information,
this chemical would seem to be a slightly better chemical to use
when considering the environment. Considering the components,
however, leads us to doubt this. See the section on zinc sulfate
above. The toxicity of copper sulfate is well known. Deciding
whether or not to control is still a
good question to consider.
Bleach
General Information: Chlorine bleach (sodium hypochlorite) can
be used on a number of surfaces contaminated with mosses including
decks, patios, walks and roofs. When used to proper concentrations
bleach is non corrosive to metals and will not stain treated areas.
One should, however, avoid contact with clothing. Brand
names of bleach especially for mosses can be found in the moss
control area in garden centers - one brand is 30seconds brand.
To apply bleach mix one part water with one part concentrate.
Use a backpack sprayer and spray liquid to dry area infected with
mosses. Keep surface wet for at lease 30 seconds.
After finishing application rinse thoroughly with water. If applying
to wood keep wet for at least 15 minutes. An alternative
to this concentration is to use four times the water. When
applying one will need to keep the surface wet for four times
as long. This concentration will cover 600 sq ft on porous
surfaces or 1800 sq ft on non-porous surfaces.
Effectiveness: Bleach applications remain effective for
up to one year, but annual applications are usually necessary.
Negative Side
Effects: Bleach at these
concentrations will be toxic to plants if left on for more than
ten minutes. After ten minutes, injury or "burning"
of foliage will occur. Since this product is toxic to fishes
and aquatic invertebrates contact with water sources should be
avoided.
Possible Alternatives: Bleach is a good alternative to many other
chemical controls, being less toxic to plants and aquatic ecosystems.
Additionally, one could consider not controlling the mosses at
all.