Insecticidal soap in the garden – use the right material

By Ralph E. Mitchell

Insecticidal soap is perhaps the most-used pesticide in my landscape.  Its use as a topical spot treatment for many soft-bodied pest insects and spider mites is unequalled.  Insecticidal soap is still an insecticide and must be applied as per label directions, but it is considered a least-toxic material within our Integrated Pest Management (IPM) toolkit.  There are commercially available products that are recommended – this does not include “home remedies”!

Insecticidal soaps contain a material called potassium salts of fatty acids.  This material is found in many natural plant and animal fats and oils and is processed so that it is toxic to a legion of soft-bodied pest insects such as aphids, mealybugs, whiteflies, soft scale insects and spider mites.  Insecticidal soaps are otherwise environmentally-friendly and   not damaging to most plants.  Most of the commercial products are formulated with a 1% to 2% of insecticidal soap rate.  A majority of plants are not damaged by this rate with the exception of some sensitive types including delicate ferns, waxy-leafed succulents and plants with hairy leaves.  There are others, so read the label to make sure that you do not accidently cause plant damage.

Unfortunately, while there are many home remedies out there, they are not research-based.  Also, as most soaps today are made using sodium hydroxide, the sodium can damage plant tissue.  The rates used to mix home remedies are also often inconsistent.  In addition, some dish detergents can remove the protective waxy layer on plant leaves causing desiccation and even remove the protective layer that helps keep out disease organisms.

Even soap/detergents have labels for use.  You can also obtain a safety data sheet with more information.  If these documents do not have specific language about using the product on plants as a pesticide, and are not registered by the EPA, then you should not use it for that purpose.    Common soaps are not qualified to be pesticide registration exempt and are not considered minimum-risk pesticides.

Insecticidal soaps are available at most garden centers and hardware stores.  They are properly formulated and very convenient to use as per label directions.  Again, even a material such as insecticidal soap has a label that must be read and followed.  These ready-to-use products have the signal word “Caution” on the label which means that the material is slightly toxic.  The insecticidal soap must get on the pests body to work, so proper application is essential.  Do not use this material if the temperatures are over ninety degrees F., when the plants are stressed, or in drought or high humidity environments.  It is suggested that if a plant’s tolerance to insecticidal soap is in question, apply some on a few leaves first before applying to the whole plant.

In conclusion, stick to commercially available insecticidal soaps that have been accurately formulated.  Home remedies, using an array of soaps and detergents, are questionable at best and have the potential to cause regrettable damage.  For more information on all types of least-toxic pesticides, please call our Master Gardener volunteers on the Plant Lifeline on Mondays, Wednesdays and Fridays from 1 to 4 pm at 764-4340 for gardening help and insight into their role as an Extension volunteer.  Don’t forget to visit our other County Plant Clinics in the area.  Please check this link for a complete list of site locations, dates and times – https://sfyl.ifas.ufl.edu/media/sfylifasufledu/charlotte/docs/pdf/Plant-Clinics-Schedule1.pdf. Our Eastport Environmental Demonstration Garden is always open to the public outside the gate at 25550 Harbor View Road.  Master Gardener volunteers tend this garden on Tuesday mornings from 8 to 10 am and are available for questions.  Ralph E. Mitchell is the Director/Horticulture Agent for the UF/IFAS Charlotte County Extension Service. He can be reached at 941-764-4344 or ralph.mitchell@charlottecountyfl.gov.

Resources:
Borden, M. A. & Dale, Dale, A. G. (2019) Managing Plant Pests with Soaps.  The University of Florida Extension Service, IFAS.
National Pesticide Information Center. Signal Words. http://npic.orst.edu/factsheets/signalwords.html.

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