the spray, so it is desirable to rinse off soap sprays
12-24 hours after application. This can be done by
following sprays with a good water rinse or foliar
feeding.
Water Quality is very important to the effective-
ness of soap sprays. Hard water reduces the effec-
tiveness of soap sprays and may even render them
useless. Using the purest water available is best, so
it is recommended to use distilled water with soap
sprays. It is best to spray a fine mist over plants
rather than drenching them. Spray bottles that can
produce a fine mist are available at dollar stores, but
commercial sprayers that have wands make it easer
to spray the underside of leaves, which is important
to achieve complete coverage. The same sprayer may
be used for soap and/or oil sprays as well as foliar
feeds, but a separate sprayer must be used for her-
bicidal sprays. As with anything that is sprayed on
plants, soap sprays are best applied when it is cool,
either in the morning or evening.
Oil Sprays
Oil sprays have been used for centuries, either
alone or in combination with soap or other ingredi-
ents to combat many of the same pests controlled
by insecticidal soaps. Oil provides an added benefit
because it has a different impact than soap on pest’s
ability to survive. It has the added benefit of help-
ing sprays to stick to leaves, and may provide some
control of funguses such as powdery mildew, as well.
Oils pose few risks to people or to most desirable
species, including beneficial natural enemies of insect
pests. This allows oils to integrate well with biologi-
cal controls.
Many gardeners use common cooking oils in
their sprays, but the type of oil used can greatly im-
pact the effectiveness of the spray. Cottonseed oil
is generally considered the most insecticidal of the
vegetable oils. Soybean oil runs a close second. The
advantage of purchasing horticultural oils specifically
designed for use on plants is that horticultural oils
are normally combined with an emulsifying agent
that allows the oil to mix well with water. Regard-
less of the oil used, the mixture usually consists of a
2 percent dilution, which is similar to that used for
insecticidal soaps. One to two teaspoons liquid soap
added to 1 quart of water is a good general guideline.
Another oil that deserves consideration for oil
sprays, and has received considerable attention as an
effective insecticide with some additional fungicidal
properties, consists of extracts from seeds of the
neem tree (Azadirachta indica).
Now that we have a good understanding of op-
tions and uses of soaps and oils as natural insecti-
cidal controls, and hopefully an appreciation for the
added benefit of combining the two, we can consider
some additional natural insecticide and fungicide
tools.
October 2017
www.GardenandGreenhouse.net
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