Dish soap on plants

All You Need to Know About Insecticidal Soap

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Are aphids gnawing on your heirloom roses? Are spider mites munching on your tomato plants? If garden pests are bugging you but you’re not a fan of toxic pesticides, take heart; there’s a safer fix. Insecticidal soap is a low-toxicity bug control solution favored by natural and organic gardeners because, when applied regularly, it maintains the ability to protect plants without resorting harsh chemical concoctions. Keep it “green” in the garden with this complete guide on when, where, and how to benefit from insecticidal soap.

What Exactly Is Insecticidal Soap?

The active ingredients in insecticidal soap are potassium salts of fatty acids (also known as soap salts), which are created when the chemical compound alkali mixes with the fatty acids found in natural oils, including castor oil, coconut oil, and olive oil. The resulting mixture kills soft-bodied garden pests such as aphids, mites, and mealybugs on contact—not beneficial hard-bodied insects like ladybugs and other beetles—all without leaving toxic residue in the soil! The catch: Insecticidal soap only works when wet, and loses its effectiveness after it dries.

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Ready-to-Use Versus DIY

A half-dozen brands of insecticidal soap can be found at your local garden center, but you also have the option to create your own solution at home from everyday products. Since both choices have their pros and cons, it’s best to weigh them before selecting the one that’s best for your needs.

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Commercial Products
Ready-to-use insecticidal soap comes packaged in a spray bottle priced between $5 and $15 for a 32-oz. bottle depending on the brand. Many gardeners like the idea of the ready-to-use product because it’s already mixed in the correct proportions so there’s very little risk of plant damage. The bottle may be labeled as “Suitable for Organic Use,” or “Safer for Plants and Vegetables,” but if a commercial bug-killer is a true insecticidal soap, its bottle will list “potassium salts of fatty acids” or “potassium laurate” as ingredients.

Insecticidal soap also comes in a concentrated solution to be mixed with water. If you buy the concentrated solution, you’ll also need to invest in a spray bottle (or pump sprayer), but purchasing this form can save you money in the long run. A 32-oz. bottle of concentrated solution costs between $15 and $30, but it will make five or six times as much spray as a ready-to-use product.

How To Make Your Own Insecticidal Soap
If you’re interested in saving even more money, you can make your own insecticidal soap. Just be sure to follow the recipe carefully: Using too much soap can make the solution too strong, which puts your plants at risk.

MATERIALS AND TOOLS Available on Amazon
– 1gallon jug of distilled water
– Mild liquid dish soap
– Vegetable oil
– Plastic spray bottle (or pump sprayer)

Fill a 1-gallon jug with water—either distilled or tap, as long as yours is not hard water (hard water reduces the effectiveness of insecticidal soap)—and leave a couple of inches at the top. Then add 2-½ tablespoons liquid dish soap (Dawn or liquid castile soap are good choices) and 2-½ tablespoons vegetable oil. Screw on the lid and shake the solution to distribute the ingredients, and immediately pour the solution into your spray bottle. You’ll want to shake the jug each time you refill the spray bottle in order to maintain the right ratio of ingredients and not distribute a formula that’s too light or too harsh. Likewise, give the spray bottle a good shake before you apply on any leaves.

Photo: istockphoto.com

Before You Spray, Consider Plant Sensitivity and Environmental Safety

Although insecticidal soaps are safe for many flowers and vegetables, a few plants are sensitive to the solution and can suffer leaf damage. Among the most susceptible plants are sweet pea, begonia, impatiens, azalea, and rhododendron. If it’s the first time you’ve treated a plant and you’re unsure whether it’s safe to use insecticidal soap, err on the side of caution and do a sensitivity test first. Spray the solution on just two or three leaves of the plant, and then examine the plant after 24 hours. If the leaves have wilted, do not treat the plant with insecticidal soap. But, if the leaves look just as healthy as they did before, it’s safe to spray the rest of its limbs regularly.

When used as directed, insecticidal soap will not harm pets, birds, or wildlife. That said, it presents a slight risk of toxicity to fish, so it’s not advisable to treat aquatic plants or plants near fish ponds.

Applying Insecticidal Soap

Spray an even mist of insecticidal soap where garden pests typically hide, including under leaves and on a plant’s main stem. The goal is to cover all plant surfaces with enough spray to make the leaves wet, but you don’t have to use so much that the solution drips off the leaves. And, because this mixture is entirely eco-friendly, it’s safe to spray directly onto fruits and vegetables such as peaches, apples, tomatoes, zucchini, and pumpkin.

Repeat the application process every four to seven days, as needed. Because insecticidal soap only kills insects when it’s wet, it’s a good idea to treat plants in early morning or late evening when the solution won’t evaporate as quickly as it will in the heat of the day.

All of the Outdoor Design and DIY Tips from BobVila.com
With fair weather having arrived finally, it’s time to turn your home improvement efforts to the backyard and your deck, porch, or patio—the parts of the home built specifically to enjoy the extra hours of sunlight. Guided by these practical pointers and inspiring ideas, you can introduce beauty, comfort, and utility to your backyard and outdoor living areas, making them as inviting and enjoyable as your home interiors.

By Scott Oneto, Farm Advisor, University of California Cooperative Extension

Soaps have been used to control insects and combat pests for hundreds of years, but their effectiveness as pesticides has been scientifically established only recently. Recently, there has been increased interest in and use of these products. This change is due to a better understanding of how to use soaps most effectively and a desire to try insecticides that are easier and safer to use than many currently available alternatives.

Photo courtesy: www.todayshomeowner.com

How soaps and detergents kill insects is still poorly understood. Researchers have been studying how soaps work in combating pests. Some soaps simply wash off the outer waxy coating of the insect’s cuticle, destroying its watertight quality and causing the insect to dry up and die. Other soaps have additional insecticidal properties that may affect the nervous system. These soaps appear to have toxic effect only against plant-eating insects and thus may spare beneficial insects such as ladybird beetles (ladybugs), lacewings, and predatory mites. In addition, high pressure sprays may wash some insects off the plant and other insects may be immobilized in soapy water, making them easier to rinse off the plants.

Soaps will kill many insect pests, including aphids, mealybugs, whiteflies, spittlebugs, rose slugs, and soft scale on most houseplants, ornamentals, and fruit trees. But because soaps have little or no residual action, sprays should be applied at regular intervals until the population is controlled or eliminated.

Soaps act strictly as contact insecticides, with no residual effect. To be effective, sprays must be applied directly to and thoroughly cover the insect. Several insecticidal soaps are available over-the-counter for control of insects and mites. Available under a variety of trade names, the active ingredient of all is potassium salt of fatty acids. Insecticidal soaps are chemically similar to many household liquid hand soaps. However, there are many features of commercial insecticidal soap products that distinguish them from the dish washing liquids or liquid hand soaps that are sometimes substituted.

Insecticidal soaps sold for control of insects:

  • are selected to control insects
  • are selected to minimize potential plant injury
  • are of consistent manufacture

Some household soap also makes effective insecticides. In particular, certain brands of hand soaps and liquid dishwashing detergents can be effective for this purpose. They are also substantially less expensive. However, there is increased risk of plant injury with these products. They are not designed for use on plants. Dry dish soaps and all clothes-washing detergents are too harsh to be used on plants. Also, many soaps and detergents are poor insecticides. Identifying safe and effective soap-detergent combinations for insect control requires experimentation. Regardless of what product is used, soap-detergent sprays are always applied diluted with water, typically at a concentration of around2 to 3 percent. (Table 1)

One of the most serious potential drawbacks to the use of Household soap-detergent sprays is their potential to cause plant injury –their phytotoxicity. Certain plants are sensitive to these sprays and may be seriously injured. For example, most commercial insecticidal soaps list plants such as hawthorn, sweet pea, cherries and plum as being sensitive to soaps. Certain tomato varieties are also sometimes damaged by insecticidal soaps. The risk of plant damage is greater with homemade preparations of household soaps or detergents. When in doubt, test soap-detergent sprays for phytotoxicity problems on a small area a day or two before an extensive area is treated.

Plant injury can be reduced by using sprays that are diluted more than the 2 to 3 percent suggested on label instructions. To reduce leaf injury, wash plants with in a couple of hours after the application. Limiting the number of soap applications can also be important, as leaf damage can accumulate with repeated exposure.

However, because of the short residual action, repeat applications may be needed at relatively short intervals (four to seven days) to control certain pests, such as spider mites and scale crawlers. Also, application must be thorough and completely wet the pest. This usually means spraying undersides of leaves and other protected sites. Insects that cannot be completely wetted, such as aphids within curled leaves, will not be controlled.

Environmental factors also can affect use of soaps. In particular, soaps (but not synthetic detergents) are affected by the presence of minerals found in hard water, which results in chemical changes producing insoluble soaps (soap scum). Control decreases if hard-water sources are used. Insecticidal soaps may also be more effective if drying is not overly rapid, such as early or late in the day.

Soaps and detergents can offer a relatively safe and easy means to control many insect pests. As with all pesticides, however, there are limitations and hazards associated with their use. Understand these limitations, and carefully follow all label instructions.

Information for this article was adapted from the University of California Division of Agriculture and Natural Resources and Colorado State University Extension. For more information on pesticides and pesticide alternatives, visit the UC IPM website.

What Is Horticultural Soap: Information On Commercial and Homemade Soap Spray For Plants

Taking care of pests in the garden doesn’t need to be expensive or toxic. Horticultural sprays are a great way to combat many issue in the garden without harming the environment or your pocketbook. Learning how to make insecticidal soap spray for plants is easy to do and the benefits are worth the extra effort.

What is Horticultural Soap?

What is horticultural soap? Horticultural soap is not a cleaning product for foliage–it is an environmentally friendly application used to eliminate small soft bodied insects such as aphids, whiteflies, spider mites and mealybugs.

Horticultural soaps may be used either on indoor houseplants or on outdoor plants, including vegetables. Insecticidal soaps have several advantages over pesticides in that they leave no nasty residue, are non-toxic to animals and birds, and do not harm beneficial insects. They are often also less expensive solutions to pest problems.

Horticultural soaps are derived from petroleum or plant oils. When horticultural soap is sprayed onto the plants’ foliage, it comes into contact with the pest and kills it. Horticultural soaps disrupt the cell membranes of the insect, resulting in suffocation. To be most effective, horticultural soaps must be applied vigilantly and thoroughly and may need to be reapplied weekly until you attain the desired result.

Insecticidal soaps also have a beneficial effect in the removal of sooty mold, honeydew and other leaf fungi.

Soap Spray for Plants

Insecticidal soap may be made at home using ingredients which are commonly used and found around the house. That said, most garden professionals recommend using a commercial soap spray that is specifically formulated for this purpose and is safer to use with more predictable results. Commercially formulated horticultural soaps are readily available at most garden supply stores and are sold as either a concentrate or ready-to-use (RTU).

How to Make Insecticidal Soap

There are several ways to make an insecticidal soap. The choice depends on the ingredients on hand and the extent to which one wants to use natural ingredients, i.e. those without perfumes or dyes.

To make insecticidal soap, simply mix the following horticultural soap recipe ingredients thoroughly:

  • Combine one cup of oil, any variety, such as vegetable, peanut, corn, soybean, etc. with one tablespoon of dishwashing liquid or other “pure” soap. Be sure to avoid any dish washing liquids which contain degreaser, bleach, or those that are for an automatic dishwasher.
  • Mix two teaspoons of this “soap” mixture to every cup of warm water and put into a spray bottle. Mix only what is needed for a one-day application.

Alternate Horticultural Soap Recipe

Homemade horticultural sprays can also be made using a natural soap product without synthetic additives or perfumes, which can be found in local natural food stores.

Combine one heavy tablespoon of liquid soap to one quart of warm water. Tap water is okay to use, but if you have hard water you may want to substitute bottled water to avoid any soap scum buildup on foliage.

To either of these soapy concoctions, a teaspoon of ground red pepper or garlic may be added to further repel chewing insects. Also, a teaspoon of cider vinegar may be added to assist in the removal of powdery mildew. Bar soap may also be used in a pinch by placing into a gallon of water and leaving to sit over night. Remove the bar and shake well before use.

There are few limitations to horticultural soaps. Just be sure to thoroughly wet the insects, and be aware that effectiveness may be limited if the soap solution dries or washes away. Phytotoxicity may occur if applied during hot days, so avoid spraying if temperatures are over 90 F. (32 C.).

BEFORE USING ANY HOMEMADE MIX: It should be noted that anytime you use a home mix, you should always test it out on a small portion of the plant first to make sure that it will not harm the plant. Also, avoid using any bleach-based soaps or detergents on plants since this can be harmful to them. In addition, it is important that a home mixture never be applied to any plant on a hot or brightly sunny day, as this will quickly lead to burning of the plant and its ultimate demise.

DIY Insecticidal Soap for Natural Pest Control

I recently moved a number of outdoor plants inside my house for the winter, and all have been doing well for the last few weeks until this week… when I found a colony of tiny pests on the windowsill, on the rim of the pot, and on the stalk of my banana plant.

I had hosed it down, inspected the leaves, and put it in fresh potting soil to prep for overwintering it, but even in the absence of pests to the naked eye, hitchhikers are always a possibility. They lay eggs on the undersides of leaves or hide in the garden soil that was still clinging to the roots.

The aphids seemed to appear overnight, and I needed to get them under control quickly yet naturally — a high concern since the plants were overwintering in our bedrooms. (Those little white specks are nymphs, or young aphids.)

Related: Organic Pest Control 101: 7 Easy Solutions for Getting Rid of Aphids

Luckily, when it comes to fast and easy (and cheap!) pest control, organic gardeners know that it takes just two ingredients to make a safe and effective pest spray: liquid soap and water.

Also called insecticidal soap, it’s the next step in managing pests when other natural, non-toxic methods (like hand-picking pests off plants, spraying them off with a sharp blast of water, or introducing beneficial insects to the garden) aren’t working.

Insecticidal soap kills common pests on houseplants and garden plants on contact; you can use the same formula indoors or out.

Commercial versions can readily be found in the gardening aisle of your local home improvement store, but DIY insecticidal soap is worth doing for its sheer simplicity and low cost. If you have a spray bottle and liquid soap handy, you’re already halfway there!

How It Works

Insecticidal soaps exploit the fatty acids in soap to suffocate small, soft-bodied insects and arthropods such as aphids, mealybugs, thrips, whiteflies, spider mites, leaf hoppers, earwigs, and immature scales (crawlers).

Upon contact, the fatty acids disrupt the permeability and structure of the insects’ cell membranes, dissolving their exoskeletons and fatally dehydrating them.

Contact is the operative word here, as insecticidal soaps only work when sprayed directly on the pests, and are only effective for as long as they remain wet. Dry soap does nothing. If you can’t see the pests, you’re not likely to get any results with the spray, homemade or not.

What To Use

Essentially, insecticidal soap is a highly refined version of liquid dish soap. But while many recipes may call for dish soap like Dawn, it’s important that you don’t use Dawn (or the like), as the detergents, fragrances, and dyes in these types of soaps can be harsh on your plants and end up doing more harm than good. (Tip: If it claims to cut grease, steer clear of it for your plants.)

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I personally like the Dr. Bronner’s line of pure-castile liquid soap, which uses fair-trade ingredients and organic oils in its formulations, and is free of additives found in commercial dish soap and hand soap. It’s not a detergent like the dish soap you use to wash dishes (which really should be called dish detergent).

Dr. Bronner’s baby unscented castile soap is the most versatile for all applications, but you can try their scented versions for a little extra repelling power in the garden.

Peppermint is known for deterring aphids, flea beetles, whiteflies, cabbage loopers, and squash bugs. Lavender repels moths, mosquitoes, fleas, and flies, while the strong aroma of eucalyptus is effective against spider mites, scales, aphids, and earwigs.

That, plus plain old tap water, is all you need for homemade insecticidal soap. It should be noted that hard water can reduce the effectiveness of the soap, so if your water is high in calcium, magnesium, or iron, use distilled or bottled water for the solution.

How to Make It

Homemade Insecticidal Soap

Makes 1 gallon of a 1% soap solution

1 gallon water
2 1/2 tablespoons pure-castile liquid soap
1 tablespoon vegetable oil (optional)

Fill a gallon-size spray container (I use this one with great results) with water, then add the soap and oil. Mix or shake the container thoroughly before using.

The oil helps the solution stick around longer after being sprayed. Since the oil can go rancid, I mix up a fresh batch of this insecticidal soap every time I need it. If you want to keep some on hand at all times, omit the oil.

To scale the recipe for smaller applications, use 2 teaspoons pure-castile liquid soap for every 1 quart water. (This spray container works well when you have fewer or smaller plants.)

Where and How to Use It

Dry conditions and hot weather (above 90°F) can increase plant stress and increase their sensitivity to the soap, so avoid spraying on a hot, sunny day and make sure your plants are well watered first.

If you’re trying to treat houseplants, be sure to protect the surroundings from overspray or move the plants to an area where you can spray freely, like a patio or garage.

Insecticidal soap is best applied in the early morning or early evening, as the cooler temperatures slow evaporation of the soap and favor better pest control. Pollinator activity tends to be low during these hours, so you have less of a chance of impairing bees, hoverflies, and other beneficial bugs.

Insecticidal soaps are not systemic insecticides — that is, they don’t absorb into plant tissue. They only work on direct contact with insects, so make sure you cover all plant surfaces where you see pests with a fine spray, including the undersides of the leaves where many pests like to hide.

(Note the emphasis on where you see pests. Simply spraying the whole plant won’t work — the soap needs to coat the insects thoroughly, not the leaves, in order to kill them.)

Spray once a week (or for more serious infestations, every 4 days) for 4 weeks until you see improvement. Any more or longer than that, and you risk leaf injury, as the soap will remove all the natural oils and waxes that protect the leaf, and thus remove the plant’s natural defenses against pests and diseases.

Speaking of leaf injury, some plants are more susceptible to soap than others, so I suggest a test spray on a small area first if you aren’t sure how sensitive your plant is.

Wait 24 to 48 hours and check for leaf damage (such as burned tips or yellow or brown spotting) before proceeding with a full application. If you do spot damage, rinse the leaves with clean water to remove any residual soap.

According to Clemson University’s Cooperative Extension, susceptible plants include hawthorn, sweet peas, cherries, plums, horse chestnut, mountain ash, Japanese maple, bleeding heart, maidenhair fern, crown of thorns, lantana, nasturtiums, gardenias, and Easter lilies, and to some extent azaleas, begonias, fuchsias, geraniums, and impatiens.

Seedlings, new transplants, newly rooted cuttings, and drought-stressed plants are also sensitive to insecticidal soap, so try to incorporate other means of pest control (like row covers or other physical barriers — I’m a fan of this mesh pop-up tent) before resorting to soap.

Remember: Less is more when it comes to spraying anything on your plants, even when you’re using natural pest control sprays.

DIY Insecticidal Soap Sources

Dr. Bronner’s Pure-Castile Liquid Soap in Baby Unscented | Dr. Bronner’s Pure-Castile Liquid Soap in Peppermint | Dr. Bronner’s Pure-Castile Liquid Soap in Lavender | Dr. Bronner’s Pure-Castile Liquid Soap in Eucalyptus | Chapin Lawn and Garden Sprayer | Chapin 48-Ounce Hand Sprayer

This post updated from an article that originally appeared on December 18, 2017.

How to Use Insecticidal Soap in the Garden

How to Use Insecticidal Soap

Soap sprays have no residual effect and only kill insects that are sprayed directly. Be sure to thoroughly wet both sides of leaves and all crevices. Repeat applications may be needed every five to seven days as new aphids or whiteflies hatch and form colonies. When using insecticidal soap to control spider mites on cucumber family crops, cover the treated plants with an old sheet for a day after treatment to enhance effectiveness while reducing risk of leaf burn. Always follow label directions for diluting insecticidal soap concentrates. Using too much can cause injury to leaves.

Soap sprays can be made at home by mixing 1 tablespoon of dishwashing liquid per quart of water. Insecticidal soaps are purer, however, and therefore less likely to injure foliage. In the vegetable garden, tomatoes and peas are the most likely plants to be damaged by soap sprays. Be careful when using any soap on leafy greens, which tend to pick up soapy flavors.

If you have hard water, use bottled water when mixing insecticidal soap, or use an already-diluted product. Minerals in hard water can greatly reduce the effectiveness of insecticidal soap.

How to Store Insecticidal Soap

Mix only as much concentrate as you will need. If not used within a few days, dispose of unused solution by diluting it with water and pouring it out in a sunny spot, far from water sources or storm drains. Store insecticidal soap in its original containers on a high shelf, out of the reach of children and pets, in a cool place where temperatures will not exceed 100 degrees. Under good storage conditions, insecticidal soap products may last five years or more.

More information on insecticidal soap is available from Clemson University.

Garden Fundamentals – become a better gardener

Insecticidal soap can be used to get rid of certain insect pests on plants, and it is one of the most non-toxic pesticides available. However, it is still a pesticide and needs to be treated as one. Many people use insecticidal soaps incorrectly, or for the wrong type of insect. In this post I will review how it works, which insects it controls and how to use it correctly. I’ll then review the problems with home made insecticidal soap.

Insecticidal soap controls aphids

Insecticidal Soap – What Is It?

Insecticidal soap, like Safer® Brand Insect Killing Soap is a true soap. It is made by reacting potassium hydroxide with long chain fatty acids. Fatty acids are made from fats.

These soaps have been specially formulated to be effective insecticides while at the same time doing very little damage to most plants.

Organic insecticidal soap controls soft body insects such as aphids, mealybugs, spider mites, and whitefly. It also controls arthropods such as earwigs, spiders, millipedes, mites, flies, and ants. It can also be used to control caterpillars and leafhoppers, but these large insects are difficult to control with this product. It does kill soft-bodied larvae of lady beetles and lacewings – beneficial insects.

This is a general pesticide that will kill both pests and beneficials.

How Does It Work?

Insecticidal soap is a contact poison. It must come into contact with the pest in order to affect it. The soap is water based and dries fairly quickly. Once dry it has no effect on pests.

Scientists don’t fully understood how they work, but the latest information suggests that the fatty acids disrupt the insects outer cell membranes. Once disrupted, contents of the cells leak out and the insect dies. For this to work well the whole body of the insect needs to be covered.

Dry soap will not disrupt the insect membrane, so it has no effect.

The dry soap will decompose fairly quickly into harmless compounds.

How do You Apply Insecticidal Soap?

If you can’t see the pest – don’t bother spraying. A pest that flies away will not be harmed.

Here are some simple instructions for Safer Brand Insect Killing Soap . For more detailed instructions see the link below (ref 1).

  1. SHAKE WELL. For best results use freshly mixed solution.
  2. DO NOT use on new transplants, newly rooted cuttings or plants stressed by drought. Avoid application when temperature exceeds 90° F.
  3. Apply when insects or signs of their damage appear. Thoroughly wet all surfaces of infested foliage and branches.

Note the comment “Thoroughly wet all surfaces of infested foliage and branches”. This does not mean you should cover the whole plant. Just spray the infected areas. Remember, you need to spray the pest to be effective – spraying leaves does not work.

If you are mixing your own diluted solutions from concentrate, use soft water, like distilled water. Hard water makes the product less effective.

Keep in mind that this is a pesticide and it can harm plants. The detailed instructions for Safers says it will harm; seedlings, new transplants, cuttings, Euphorbias, delicate ferns, bleeding hearts, azaleas, sweet peas to mention a few. See the full instructions for a complete list.

Home Made Insecticidal Soap

There are many recipes on the internet for home made, DIY insecticidal soap. My post, Dish Soap Can Damage your Plants discusses the problem with these in detail. Home made solutions using soaps found in the home are chemically not the correct type of soap and are more likely to be phytotoxic (poisonous) to your plants – they might even kill them.

Dish soap is not even a soap – it is a detergent. You can’t make insecticidal soap using a detergent because they are very toxic to plants.

Insecticidal Soap Products

Clemson University Extension office (ref 3) provides this list of available products:

  • Bonide Insecticidal Soap Concentrate;
  • Safer Insect Killing Soap Concentrate;
  • Schultz Garden Safe Insecticidal Soap Insect Killer Concentrate;
  • Natural Guard Insecticidal Soap Concentrate;
  • Espoma Earth-tone Insecticidal Soap Concentrate;
  • Concern Rose & Flower Insect Killer II
  • Raid Earth Options Insecticidal Soap
  • Lilly Miller Worry Free Insecticidal Soap
  • Whitney Farms Insecticidal Soap
  • Bayer Advanced Natria Insecticidal Soap

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UConn Home & Garden Education Center

Insecticidal Soaps

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Insecticidal soaps can be a valuable tool to manage insect and mite pests on houseplants, vegetables, fruits and ornamentals. Soaps control many targeted pests with fewer potential adverse effects to the user, beneficial insects and the environment compared to more traditional pesticides. To be most effective, it’s important to understand how insecticidal soaps “work,” to know their mode of action, and to recognize their benefits and limitations.
What is insecticidal soap?
Insecticidal soaps are potassium salts of fatty acids. A soap is made from the action of an alkali such as potassium hydroxide on a fat. Fats consist mainly of fatty acids. Commercial products contain a blend of selected fatty acid chain lengths.
How do insecticidal soaps work?
Insecticidal soaps work only on direct contact with the target pests. The most common soaps are made of the potassium salts of fatty acids. The fatty acids disrupt the structure and permeability of the insects’ cell membranes. The cell contents are able to leak from the damaged cells, and the insect quickly dies. There is no residual insecticidal activity once the spray application has dried. Insecticidal soaps rapidly degrade and wash off of leaf surfaces.
Benefits of Insecticidal Soap
Insecticidal soaps are most effective on soft-bodied pests such as aphids, adelgids, lacebugs, leafhoppers, mealybugs, thrips, sawfly larvae (pear and rose slugs), scale insects (especially scale crawlers), plant bugs, psyllids, spider mites and whiteflies. Insecticidal soap has less effect against insect eggs. Insecticidal soap is also less effective against hard bodied pests such as beetles. Some soaps are labeled for suppression of powdery mildew on certain plants.
Soaps have low mammalian toxicity. However, they can be mildly irritating to the skin or eyes. Insecticidal soaps are biodegradable, do not persist in the environment, and they do not contain any organic solvents. Many formulations of insecticidal soap can be used on various food crops up to the day of harvest.
Limitations in the Use of Insecticidal Soap
As mentioned earlier, once an insecticidal soap spray has dried, there is no residual activity because insecticidal soaps work only on contact. If an insect has not been coated with the spray, it will not be affected by walking over or ingesting plant material that has been treated with soap.
As with any contact insecticide, familiarity with the biology and life cycle of the targeted pest will lead to more effective management. For example, insecticidal soaps are useful in controlling azalea lace bug nymphs but will have no effect against lace bug eggs. In addition, all stages of the lace bug are found on the undersides of leaves. Spraying only on the upper surfaces will have no effect, as the treatment will not come in contact with the targeted pest. Regular scouting to detect when the lace bug nymphs hatch from the eggs will determine the best time for treatment.
Plants that may be sensitive to applications

  • Insecticidal soaps may cause phytotoxicity (causing plant injury) symptoms, such as yellow or brown spotting on the leaves, burned tips or leaf scorch on certain sensitive plants.
  • Plant sensitivity can be influenced by pest pressure, cultivar, plant vigor, environmental conditions, spray concentration, pH of spray mixture as well as the timing, number and frequency of applications.
  • Plants under stress such as hot (greater than 90 °F), humid or drought conditions, young transplants, unrooted cuttings and plants with soft young growth are more likely to develop phytotoxic symptoms and should not be treated with soap.
  • Do not apply to very sensitive plants such as horse chestnut, Japanese maple, mountain ash, bleeding heart or sweet peas.
  • Begonia, chrysanthemum, Crown of Thorns, cucumber, delicate ferns, narrow leaf evergreens (especially when stressed or when tender new growth is present), dieffenbachia, fuchsia, gardenia, impatiens, jade plant, lantana, ornamental ivy, palms, poinsettia, redbud, river birch, schefflera, Zebra plant and some succulents may be sensitive. The open blooms or flowers of many plants may also be injured.
  • Glaucous bloom on spruces and waxy bloom on grapes may be altered.When uncertain, spot treat a portion of the cultivar, and wait at least 24 hours to see if any phytotoxic (plant damaging) symptoms develop before treating an entire group of plants.
  • Dishwashing soaps and detergents are designed to remove grease from dishes and may cause plant damage by dissolving the waxy cuticle on plant leaf surfaces. There is increased risk of plant injury with the use of dishwashing soaps and detergents (not labeled as a pesticide) when used as a spray.

How to Apply
Insecticidal soaps should be applied when conditions favor slow drying to maximize effectiveness, e.g., in the early morning hours with dew coverage or in the early evening. Avoid treating with soaps on hot sunny afternoons which promote rapid drying. Thorough coverage is vital for the soap to be effective: Spray thoroughly, but not beyond the point of runoff. Repeat applications may also be needed as determined by follow up scouting.
Insecticidal soap mixed in hard water with a high mineral content may be less effective and more toxic to the treated plants. A precipitate (soup scum) may be formed when the metal ions (e.g., calcium, iron or magnesium) found in hard water bind to the fatty acids in the soap. Because insecticidal soaps are toxic to fish and aquatic organisms, do not use near bodies of water.
In summary, soaps are effective tools in an integrated approach toward pest management if they are used properly with an understanding of their limitations and benefits. Carefully follow all label instructions.
Despite good cultural practices, pests and diseases at times may appear. Chemical control should be used only after all other methods have failed.
For pesticide information or other questions please call toll free: 877-486-6271.
Integrated Pest Management Program Department of Plant Science and Landscape Architecture UConn Extension
By Leanne Pundt, Extension Educator, University of Connecticut. 1993, Updated 2015.
Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, the Dean of the College, Cooperative Extension System, University of Connecticut, Storrs. The Connecticut Cooperative Extension System is an equal opportunity employer and program provider. To file a complaint of discrimination, write USDA, Director, Office of Civil Rights, Room 326-W, Whitten Building, Stop Code 9410, 1400 Independence Avenue, SW, Washington, DC 20250-9410 or call (202) 720-5964.

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