Soaps, Detergents, and Pest Management

The Master Gardener Volunteer Program is thankful to UF/IFAS Extension faculty Dr. Adam Dale and Dr. Matthew Borden for their publication Managing Plant Pests with Soaps. For further information, please reference this publication and contact your county Extension office or the UF/IFAS Pesticide Information Office if you have any questions.

A home garden of raised beds, pinestraw walkways, and colorful pinwheel stakes — In 2020, public health concerns led to a boom in home vegetable gardening, and in questions about appropriate pesticide use. Credit: Tyler Jones, UF/IFAS.

Today more people than ever recognize the importance of using pesticides wisely, protecting pollinators, and managing gardens with low-impact strategies (like integrated pest management). Soaps come up often in conversation on these topics, especially in ones about low-impact or organic pest management.

In English, we use the word “soap” to refer to a number of products: hand soap, dish soap, castile soap, laundry soap, and insecticidal soap, to name a few. They may share a name, but these “soap” products are actually very different. Still, because people are familiar with soaps’ use in the kitchen, laundry, and bathroom, many feel safe using them in the garden, too.

To protect consumers and the environment, soaps designed for use as pesticides are evaluated by the Environmental Protection Agency (EPA). They are registered as insecticidal soaps and their labels contain directions for use, precautionary statements, and instructions for storage and disposal. They also list relevant environmental, physical, and chemical hazard warnings, such as “hazardous to aquatic invertebrates.” As tempting as DIY recipes can be, ingredient and concentration inconsistencies make these concoctions an unknown danger to yourself, your plants, and the environment. Below are some common misunderstandings about soap and detergent use in home gardens.

Misunderstanding #1: Dish soap is a natural, safe alternative to pesticides.

Image of a bottle of blue Dawn liquid dish soap showing the front and back labels with a yellow arrow pointing to the back label — The label is the law. Instructions for use are found on the label of all cleaning products. Credit: Procter & Gamble

Research shows: Dish “soaps” are not true soaps; they are detergents, synthetically produced and chemically designed to be powerful cleaners.

Cleaning products (including detergents like Dawn®, Joy®, and Palmolive®) have labels that explain how they may safely be used. As with all other chemicals, the label is the law. If the instructions do not include garden or pesticide use, then the product was not intended to be used in that manner. It may even be dangerous to do so.

Understandably, companies package cleaning products in ways that help their consumers feel the product will be safe and effective. Advertising for these products often includes words like “gentle” or “natural,” along with images of fields and flowers. Make no mistake — no matter how attractively packaged, detergents are not appropriate pest control for organic or conventional gardening.

Misunderstanding #2: Soaps are mild; they don’t hurt plants.

A vegetable leaf with damage from fertilizer directly touching it — Follow product use directions to avoid leaf burn.
Credit: University of Maryland Extension

Research shows: As discussed above, most dish soaps are actually detergents. To do their job well, they must be powerful enough to strip oils and other lipids from man-made surfaces.

Plant leaves are covered with a layer of waxy lipids. This waxy cuticle layer protects them from losing water and from viruses, bacteria, funguses, and other pathogens. Even when watered down, detergents cut through these protective layers. The result is often damaged, dry, crispy leaves.

Even true soaps can damage plants depending on which active ingredients they include. Most soaps intended for hygienic uses are made with sodium hydroxide. This ingredient is a powerful, modern lye. The sodium in this formula can cause significant damage to plant tissue. Insecticidal soaps, on the other hand, are intended for use on plants. They are made with potassium hydroxide, which can be used without damaging plant tissue.

Misunderstanding #3: Soaps kill the bad bugs without hurting the good bugs.

A red ladybug with black spots sitting on a leaf — Soaps affect both the good bugs and the bad bugs. Check for beneficial insects before you apply any form of pesticide. Credit: UF/IFAS

Research shows: Soaps and detergents don’t discriminate between good bugs and bad bugs. The ingredients that damage soft-bodied insects and mites also attack beneficial insects and funguses. Insecticidal soaps, although designed for use on plants, also damage pest and beneficial insects indiscriminately.

When it comes to our gardens, we know that insects can be helpful, harmful, or harmless. No matter which pest control option we choose, protecting the good bugs will require education and effort.

More about Home Recipes for Pesticides

On the topic of pest control there is a lot of conflicting information and room for error. Using products not registered by the EPA as makeshift pesticides is not recommended by UF/IFAS for a number of reasons, including safety hazards to plants, animals, and people. Few of the recipes available online come from research-based sources. In fact, due to an increased interest in sustainable home food production, many recipes are simply “click bait,” offering advertisements rather than sound garden advice. Finally, application of unregistered chemicals onto crops sold as food is illegal.

Any soap, even the insecticidal soaps intended for garden use, can injure plants if used incorrectly. Often issues with homemade pesticide formulas are related to inconsistent ingredients and concentrations.

Ingredients to avoid

Ingredients like vinegar and alcohol are phytotoxic; this means they cause leaf burn and other plant injuries. These should not be applied to plant tissues. Even familiar products, like Procter & Gamble Ivory® soaps, frequently change their ingredients. They are not intended for use on plants and their potential toxicity is unknown.

Worse still, some home recipes for pest control call for mixing different products. This is dangerous! Common cleaners that may be safe to use by themselves can be toxic to humans when they are used together.

A thumbnail image of a larger infographic on household chemicals to avoid mixing, click for printable, visit https://www.usfa.fema.gov/operations/infograms/031920.html for text version — Mixing cleaning products, even for outside use, is always a serious risk to your health. Credit: UF/IFAS (larger printable version)

Concentration matters

Similarly, home recipes for insecticidal soaps are inconsistent in the rate of application (the amount of soap relative to the amount of water). Some recipes recommend one teaspoon of soap per quart of water; others call for a whole quarter of a cup.

Properly registered and EPA-approved insecticidal soaps are usually only 1-2% soap by volume. This rate minimizes damage to the plant but is still effective as a pest control. Labels also include important information about plant species that are sensitive to the product’s ingredients. Regardless of the formula, plants under drought stress, in excessive humidity, or in heat above 90 degrees Fahrenheit should never be treated with soaps.

Regardless of which product you choose, always read the label first — before you buy and before you use.

If you have questions about soaps or pesticide use, please contact your county Extension office or the UF/IFAS Pesticide Information Office for more information about pesticide safety.