FEATURESTORY
by Nick Fraser
Soap, Oil and Other Homemade Insecticides and
Fungicides
B
ecause they are often primary components
of many home remedies, it helps to have a
good understanding of the use of soaps and
oils for treating plant pest problems before
looking into various other homemade potions.
Soap Sprays
There are three types of soap that gardeners
through the ages have used to treat a number of
plant insect problems. All soaps are fatty acid-based
products, and to varying degrees, are one of the saf-
est sprays to use in the garden. They primarily kill
soft-bodied insects, such as aphids, mealybugs, spider
mites, thrips, whitefl ies and immature leafhoppers.
Repeated applications at one week intervals are gener-
ally necessary to control high pest populations.
I remember my grandmother washing dishes in
a large pail in the sink and then dumping the soapy
water over various plants in the garden. The belief
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was that the soapy water acted both as an insecticide
and soil nutrient. Many gardeners have been add-
ing small quantities of dish detergent with water and
spraying plants with good results for years.
There are other gardeners who prefer to use
either natural liquid soap, available at health food
stores, instead of dish detergent, and there are some
valid reasons. Most dishwashing detergents have anti
-bacterial properties that may have some harmful ef-
fects on plants, particularly if the sprays are mixed too
strong.
The third option is to spend the extra money and
purchase an insecticidal soap specifi cally formulated
for use on plants. Commercially formulated insecti-
cidal soaps are better than home remedies because
they have been tested to be safe on a variety of plants.
Perhaps the biggest mistake gardeners make in
using soap sprays is not in the soap they select, but
in mixing the spray too strong. Commercial insecti-
cidal soaps will come with mixing instructions, and it
is best to start half strength until you can determine
how various plants react to spraying. A conservative
mixture for soap spray is 1 to 2 teaspoons liquid soap
added to 1 quart of water. A few drops of cooking oil
can be added to help the mixture cling to leaves bet-
ter.
Guidelines for Insecticidal Soap
Insecticidal soap is a contact material, meaning
that insects must come into direct contact with spray
for it to be effective. There is no residual benefi t of
www.GardenandGreenhouse.net
October 2017