Chemical control of mosses on trees
and shrubs is not commonly attempted by the average homeowner
because these products are fairly toxic and require use of special
protective equipment when handling them. You may want to hire
a professional if you desire to remove mosses from trees and shrubs
using chemicals.
Control of mosses is generally achieved using either copper sulfate
or lime sulfur. Professional tree care companies and the Oregon
State Extension Service recommend these chemicals as effective
treatments. Even though they may be effective in killing the moss,
the effect is short lived. Furthermore, the treatment is unnecessary,
because mosses are benign and do not parasitize the trees and
shrubs. Why use these polluting chemicals if they are unnecessary?
Chemicals are sprayed on the mosses
during the winter dormancy period. They can damage leaves if applied
during active growth and can also damage evergreen leaves and
needles. They are corrosive, so care must be taken to keep them
from drifting onto painted or metal surfaces. These chemicals
should only be used according to the label and should only be
used on plants that are listed on the label (Davison
and Byther, 1999).
Copper Sulfate
Copper sulfate is often used as a fungicide or algaecide, but
it can also work to control mosses if used during the dormant
period when the plant is not growing. It is available as a dust,
wettable powder and fluid concentration. It is used primarily
by farmers and may not be available at all stores. Tri- Basic
copper sulfate and Bordeaux (copper sulfate formulated with lime)
are formulations that have been used to control mosses on trees
and shrubs. There are a lot of products available and you should
consult labels before attempting to use any of them. A sprayer
is generally used to apply copper sulfate on to trees.
Effectiveness
Copper sulfate is effective at killing mosses when used properly.
It works by disrupting photosynthesis. It will also damage plants,
especially if they are in active growth. You will have to continue
applying it every few years if you don't improve cultural conditions
like sunlight and air circulation because the mosses will return.
The dead mosses will also persist after spraying for a while before
they weather and fall off the branches.
Side Effects
Copper sulfate is a moderately toxic product and care should
be taken when handling this pesticide. Poisoning and even death
has been attributed to ingestion of copper sulfate (EXTOXNET
web site). Protective equipment including long sleeve clothes,
mask and safety glasses should be used (Meister,
1996). Chronic effects that have been documented include liver
disease and anemia due to long term exposure to applicators over
several years. Refer to EXTOXNET
web site for more details. This product can also be harmful to
wildlife, especially aquatic organisms like fish. Copper sulfate
should not be used near creeks or bodies of water.
Lime sulfur
Lime sulfur is used as a fungicide but is also effective in controlling
mosses when used during the winter months that mosses are actively
growing and the trees or shrubs are dormant. It is used primarily
by farmers and may not be available at all stores. You should
consult labels before attempting to use it. You will use a sprayer
to apply it to trees. It smells like rotten eggs.
Effectiveness
Lime sulfur is effective for controlling mosses on trees and
shrubs. You will need to reapply it every few years if you do
not address the causes of moss growth.
Side-Effects
This product is very toxic. It can cause permanent damage to the
eyes. Protective equipment including a respirator, safety glasses
and long sleeve clothes should be worn (Meister,
1996). This product is corrosive and will cause damage to
painted surfaces. There is less information available on the effects
to wildlife. This product is also used as an insecticide and may
harm beneficial insects like honeybees. It persists on the plant
for a while by leaving a sulfur residue after it dries. This will
wash off after winter rains.