- An effective alternative for
garden insecticides -
Insecticidal soap can be used as a safe and
inexpensive alternative to garden insecticides in
many pest management situations. Be cautious,
however, because old, oxidized soap can damage your
plants. A simple DIY test is available to protect plants
from this damage.
What is insecticidal soap?
Insecticidal soap is a very safe
and effective alternative to conventional insecticides
for many garden and landscape pests. It is used mainly
for soft-bodied pests like aphids,
thrips, scale insect crawlers
and spider mites
but is also a very effective leaf wash to remove aphid
honeydew, sooty mold and other leaf debris.
All soaps are made from the fatty-acids
of either plant or animal oils. Chemically, soaps are
salts of the fatty acid portion of fats and oils.
Insecticidal soap is simply a highly refined version
of ordinary liquid soap. However, do
not jump to the conclusion that you can
substitute ordinary dish soaps, or homemade soaps, for
genuine insecticidal soap. Doing so will damage
your plants and probably won't be very effective.
Fresh 2% soap solution
(jar on left). The slight milky color is
normal. If the solution turns cloudy, or a
white precipitate forms (jar on right), don't use it and buy new soap concentrate.
Insecticidal soaps will not usually
harm beneficial species such as predators and
parasites and are generally very safe for the
applicator. Soap concentrates are less
expensive in the long run, and easier to store, than
ready-to-use packaging. However, always do what I
call a jar test to be certain that the
concentrate has not spoiled.
DIY insecticidal soap "jar test"
As soap concentrate ages it oxidizes
which causes it to turn dark
brown. Old, oxidized soap has the potential
to burn plant foliage. Solutions made from
old soap concentrate often exhibit a white
precipitate (see jar on right, above) when mixed
with water and should be discarded. Old soap
concentrate can be used as a cleaner like ordinary
liquid soap just don't put it on your plants!
Mix the soap concentrate as a 1-2%
solution and pour into a jar. A 1-2% solution is about
1-2 oz. of concentrate in 1 gallon of water (always
follow label instructions). A white precipitate
will form almost immediately if the concentrate has
gone bad, discard the solution if this happens and
replace with new soap concentrate.
Using insecticidal soap in your
Insecticidal soap is generally used as
a 1-2% solution (1-2 oz. per gallon). Mix soap
concentrate in a clean 1 quart sprayer. Plan to
treat in the morning of a warm day when the plants
will be able to dry before evening. Spray plants
with a coarse spray of plain water from the garden
hose. Next, thoroughly spray plants with soap
solution covering all surfaces. Finally, wait 30
minutes then wash soap off with water. The last step
will prevent soap solution from damaging tender leaf
tissue (see Using
Insecticidal Soap To Control Aphids and Using
Insecticidal Soap To Control Spider Mites for
Insecticidal soaps can be found at garden supply stores. For
most gardeners the pint size will make a year's worth of working solution. At
the end of the season use what's left of the concentrate to clean the inside of
the greenhouse and your pesticide sprayers. Do not use year-old concentrate!
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